Centrifuges are indispensable tools in the laboratory. However, their use often presents various challenges; many users are unfamiliar with the concepts of "balancing" and "unit conversion between RPM and g," which frequently leads to operational errors. Therefore, I would like to provide a systematic overview of centrifuges, focusing specifically on these two key topics.

Centrifuge Principles

The operating principle of a centrifuge primarily relies on centrifugal sedimentation; by harnessing the centrifugal force generated through rotation, it facilitates the separation, concentration, and purification of substances with varying densities within a solution.

When a suspension is subjected to high-speed rotation, the immense centrifugal force causes the suspended microscopic particles—such as organelles or precipitates of biological macromolecules—to settle at a specific velocity. This process facilitates the separation, concentration, and purification of the solution; the settling velocity of the particles is determined by the centrifuge's rotational speed, as well as the mass, size, and density of the particles themselves.

When a suspension—defined as a mixture in which minute solid particles are suspended within a liquid medium—is allowed to stand motionless, the influence of the gravitational field causes the suspended particles to gradually settle. The rate of this sedimentation is contingent upon the size, morphology, and density of the particles, as well as the intensity of the gravitational field and the viscosity of the liquid medium. For instance, particles such as erythrocytes (red blood cells), which measure several micrometers in diameter, exhibit an observable sedimentation process under the influence of normal gravity. Furthermore, the sedimentation of substances within a medium is invariably accompanied by the phenomenon of diffusion.

Diffusion is a phenomenon of mass transfer resulting from the thermal motion of particles, driven primarily by density gradients. For particles smaller than a few micrometers—such as viruses or proteins—which exist in solution in a colloidal or semi-colloidal state, it is impossible to observe the sedimentation process using gravity alone.

This is because the smaller the particles, the slower their sedimentation rate, while the effects of diffusion become correspondingly more pronounced. Since diffusion hinders sample separation, increasing the gravitational force can help overcome these adverse effects, thereby enabling the separation of biological macromolecules.

The Function of Centrifuges and Relative Centrifugal Force

A centrifuge utilizes the powerful centrifugal force generated by the high-speed rotation of its rotor to compel particles suspended in a liquid to overcome diffusion and accelerate their rate of sedimentation, thereby separating substances within a sample that possess different sedimentation coefficients and buoyant densities. But what exactly is centrifugal force?

In the context of relativity, centrifugal force refers to the force experienced by a point mass undergoing curvilinear motion, which acts to pull it toward the center of its trajectory. When the external force acting upon an object is insufficient to provide the centripetal force required for its motion, the object will tend to move in a direction away from the center of the circle. This phenomenon—the object moving away from the center—is known as the centrifugal phenomenon; it is also referred to as centrifugal motion. Centrifugal motion occurs as a result of the absence or insufficiency of centripetal force.

Centrifugal action is based on the principle that any object undergoing circular motion at a specific angular velocity is subject to an outward centrifugal force. The magnitude of the centrifugal force (Fe) is equal to the product of the centrifugal acceleration (ω²r) and the mass of the particle (m):

Relative Centrifugal Force (RCF) refers to the magnitude of the centrifugal force acting on a particle within a centrifugal field, expressed as a multiple of Earth's gravity; its unit is the gravitational acceleration "g." Since the rotor radii—or the distances from the centrifuge tubes to the center of the axis of rotation—vary among different centrifuges, the resulting centrifugal forces also differ.

Consequently, scientific literature commonly employs the term "Relative Centrifugal Force" or the notation "number × g" to specify centrifugal force—for instance, "25,000 × g," which indicates a relative centrifugal force of 25,000. Provided that the RCF value remains constant, a sample will yield identical results regardless of which centrifuge is used. Relative Centrifugal Force is, in essence, the ratio of the centrifugal force to the force of gravity:

Generally, during low-speed centrifugation, relative centrifugal force is often expressed in terms of rotational speed (rpm), whereas during high-speed centrifugation, it is expressed as a numerical value followed by "xg."

Centrifuge Construction and Types

Here, centrifuges are classified into three categories based on speed: low-speed centrifuges, high-speed centrifuges, and ultra-high-speed centrifuges.

Low-speed centrifugestypically operate at speeds below 10,000 rpm and are suitable for the separation of biological samples such as cells and microorganisms. High-speed centrifuges operate within a range of 10,000 to 30,000 rpm and are frequently used for the separation of macromolecules, such as proteins and nucleic acids. Ultra-high-speed centrifuges operate at speeds exceeding 30,000 rpm and can be utilized for the separation of minute particles, such as viruses and subcellular organelles.

The structure of a centrifuge is relatively simple, consisting primarily of key components such as an electric motor, a centrifuge rotor, a speed controller, a timer, centrifuge tubes, and a base. The following section introduces three main types of centrifuges:

1. Low-Speed Centrifuge

Its structure is relatively simple, comprising key components such as an electric motor, a centrifuge rotor, a speed controller, a timer, centrifuge tubes, and a base.

(1) Electric Motor: The primary component of the centrifuge, typically of the series-excited type. It consists of two parts: the stator and the rotor.

(2) Centrifuge Disc (and Rotor Head): The centrifuge disc is commonly made of cast aluminum; it features a flat-topped conical shape with a central circular aperture. It is mounted onto the motor shaft at the upper end of the motor and then secured in place by tightening a nut. The disc is fitted with 6 to 12 symmetrically arranged holes, angled at 45 degrees, designed to accommodate test tubes.

(3) Speed Control Mechanism: The speed control mechanism (for the electric motor) involves connecting a multi-tapped choke coil or a disc-type variable resistor in series between the power supply and the motor.

(4) Centrifuge Tubes: Centrifuge tubes are primarily manufactured from plastic or stainless steel. Plastic centrifuge tubes are equipped with caps; prior to centrifugation, these caps must be securely fastened. Stainless steel centrifuge tubes possess high structural strength, resist deformation, and are resistant to heat, freezing temperatures, and chemical corrosion.

2. High-Speed (Refrigerated) Centrifuge

This apparatus comprises a rotating mechanism, a speed control system, a temperature control system, a vacuum system, a centrifugation chamber, a rotor head, and various safety protection devices. Due to its high rotational speed and the inclusion of a low-temperature control unit, the temperature within the centrifugation chamber can be regulated and maintained within a range of 0°C to 40°C. The rotational speed, temperature, and duration can all be controlled with strict precision, and their values are displayed via either analog pointers or digital readouts.

(1) Rotating Assembly: Motor, rotor shaft (and its connecting components);

(2) Speed Control System: Reference voltage source, speed regulator, current regulator, power amplifier, motor, speed sensor, etc.;

(3) Vacuum System: Designed to overcome air friction (which generates heat) and ensure the centrifuge attains the rotational speed required for normal operation;

(4) Temperature Control Unit: Composed of four main components: a compressor, a condenser, a capillary tube, and an evaporator;

(5) Safety Protection Devices: Main power supply overcurrent protection, drive circuit overspeed protection, refrigeration unit overload protection, and operational safety interlocks.

3. High-Speed (Refrigerated) Centrifuge: Consists of a drive assembly, a speed control system, a temperature control system, a vacuum system, and a rotor.

How to Balance a Centrifuge?

A centrifuge rotates thousands of times per minute; this means that even the slightest weight imbalance around the rotor will be amplified, potentially causing the instrument to wobble or vibrate. This compromises its performance and reliability, shortens its service life, and—in the worst-case scenario—could lead to the centrifuge exploding, thereby injuring laboratory personnel. Therefore, understanding how to properly balance a centrifuge is absolutely essential.

1. Balancing Fixed-Angle Rotors

For balancing fixed-angle rotors, one generally needs only to keep the "Center-Symmetry Method" in mind. Taking the 12-place fixed-angle rotor shown in the figure below as an example, samples can be positioned by adhering to this principle.

2. Horizontal Rotor Balancing

In practical applications, the most vexing challenge is balancing horizontal rotors. This is because one must not only ensure the symmetry of the centrifuge tubes within a single bucket but also verify that the tubes in the opposing bucket are properly balanced. When balancing under these circumstances, two key principles must be strictly observed:

(1) When placing centrifuge tubes within a single bucket, ensure that the bucket's center of gravity is positioned precisely at its geometric center;

(2) When placing centrifuge tubes in the opposing bucket, use the placement in the first bucket as a reference point; strictly adhere to the principle of symmetry relative to the rotor's central axis to determine the appropriate placement positions.

3. Balancing Odd Numbers of Tubes

Furthermore, situations involving the balancing of an odd number of tubes are frequently encountered. When faced with such a scenario, most students typically opt to insert a "blank" balancing tube (filled with water). While this approach is simple and straightforward, it can prove rather cumbersome in experiments involving frequent centrifugation or where sample masses and volumes vary significantly. So, how exactly should one proceed when encountering such a situation? Taking a 24-place fixed-angle rotor as an example, the procedure can be categorized into three distinct scenarios: If there is only one tube or exactly 23 tubes, the only option is to prepare a single tube of water to serve as the counterweight;

(1) The "Triple-Placement" Balancing Method: When dealing with an odd number of centrifuge tubes that constitute a multiple of three—such as 3, 6, 9, 15, or 21 tubes—they can be arranged in a clockwise pattern, as illustrated in the diagram below;

(2) The "2-Unit Plus 3-Unit" Balancing Method: When dealing with a total of 5, 7, 11, 13, 17, or 19 units, one may adhere to the principle of central symmetry by first balancing a group of three units, and then balancing the remaining two units; when combined, the overall system remains balanced.

Ultimately, the balancing of a centrifuge rotor is governed by the principle of symmetry: the relative masses of the two centrifuge tube cups situated on a single moment arm must remain identical. In practice, simply loading the rotor wells sequentially—following a pattern such as 2+2+2...+3—ensures that each set remains balanced, thereby guaranteeing a foolproof operation. The illustrative diagram below visualizes this principle with even greater clarity:

What is the relationship between rotational speed (rpm) and relative centrifugal force (g)?

For centrifuges, the units typically used to indicate speed are revolutions per minute (rpm) and centrifugal force (g). In this context, "g" is sometimes also denoted as RCF (Relative Centrifugal Force). The calculated relationship between these two units (where *r* represents the radius) is as follows:

Let's take an example: assume a rotational speed of 3000 rpm and an effective centrifugal radius of 10 cm (a parameter typically found in the centrifuge's instruction manual). Substituting these values into the formula yields: RCF = g = 11.18 × 10 ⁻⁶ × 10 × (3000)² = 1006.2 (g). From this, it becomes evident that the discrepancy between the centrifugal force and the rotational speed is primarily determined by the centrifugal radius.

In practice, no one actually uses this formula to perform precise calculations; furthermore, the vast majority of centrifuges offer the option to adjust settings using either rotational speed or centrifugal force. However, if one were to identify the most accurate method of expression, it would undoubtedly be through centrifugal force (xg); theoretically speaking, provided the centrifugal force remains constant, the resulting separation effect should be fundamentally identical across different centrifuges. Rotational speed, on the other hand, does not offer this consistency; even at the same rotational speed, variations in rotor radius can significantly alter the resulting centrifugal force.

The formula also reveals that the relationship between centrifugal force and rotational speed is not linear. Generally, at lower rotational speeds, the numerical value of the speed exceeds that of the centrifugal force. As the rotational speed increases, the numerical disparity between the two gradually narrows—eventually reaching a point of parity—before the relationship reverses, ultimately resulting in the numerical value of the rotational speed falling below that of the centrifugal force.

To help you gain a deeper understanding, I have provided the actual specifications of a specific low-temperature centrifuge to help reinforce the concepts (please refer to the image above). While the specific values vary across different centrifuges, the underlying principles remain consistent.

When we encounter a centrifuge, the first questions that come to mind are: What exactly is a centrifuge? And what are its underlying principles? We have provided a detailed explanation of these principles in our article, "Low-speed Centrifuge: Principles, RCF Conversion, Rotor Types & Practical Usage Tips"—so if you are unfamiliar with the subject, we recommend reading that piece first. However, when using a centrifuge for the first time, one question frequently arises: How do you ensure the centrifuge remains balanced? In the article that follows, we will explore this very topic together!

I. Why Balancing a Centrifuge Is Crucial

An unbalanced centrifuge rotor can lead to consequences ranging from minor issues—such as machine wear and sample loss—to severe outcomes, including serious injury or even fatalities. Mastering the correct balancing techniques is therefore paramount: fixed-angle rotors should adhere to the "center-symmetrical method"; horizontal rotors require careful consideration of both the center of gravity of the swinging buckets and the principle of symmetry; and for an odd number of tubes, a flexible combination of "2x + 3x" balancing sets should be employed. Ensuring that every set of centrifuge tubes is properly balanced is the only way to safeguard both experimental integrity and personal safety, thereby preventing accidents before they occur.

Since the invention of the centrifuge in the 19th century, the risks associated with unbalanced rotors have been a persistent concern. At the milder end of the spectrum, an imbalance can cause excessive wear on the machine's drive shaft—thereby shortening the centrifuge's service life—or result in tubes dislodging and samples being lost; at the severe end, it can lead to serious injury or loss of life. The most effective way to mitigate the dangers posed by an unbalanced rotor is to learn and apply the correct balancing procedures!

II. How to Balance a Centrifuge

1. Balancing Fixed-Angle Rotors

For balancing fixed-angle rotors, one generally needs only to keep the "Center-Symmetry Method" in mind. Taking the 12-place fixed-angle rotor shown in the figure below as an example, samples can be positioned by following this principle:

2. Balancing Horizontal Rotors

In practical applications, the task that causes the most headaches for researchers is balancing horizontal rotors. This is because one must not only ensure the symmetry of the centrifuge tubes *within* a single bucket but also ensure that the tubes in the *opposing* bucket are balanced relative to it. When balancing under these circumstances, two key principles must be strictly observed:

When placing centrifuge tubes within a single bucket, ensure that the bucket's center of gravity remains precisely at its geometric center;

When placing centrifuge tubes in the opposing bucket, use the placement configuration of the first bucket as a reference point, strictly adhering to the principle of symmetry relative to the rotor's central axis, and then position the tubes accordingly.

Taking the 4×14-hole horizontal bucket rotor shown in the figure below as an example, samples can be loaded by following the aforementioned principles:

3. Balancing an Odd Number of Tubes

Furthermore, situations involving the balancing of an odd number of tubes are frequently encountered. When faced with such a scenario, most students typically opt to insert a "dummy" balancing tube (filled with water). While this method is simple and straightforward, it can prove rather cumbersome in experiments involving multiple centrifugation cycles or where sample masses and volumes vary significantly. So, how exactly should one proceed when encountering such a situation? Using a 24-place fixed-angle rotor as an example, the process can be categorized into three distinct scenarios:

If there is only 1 tube or exactly 23 tubes: In this specific instance, there is no alternative; one must simply prepare a balancing tube filled with water to achieve equilibrium.

The "Triple-Multiple" Balancing Method: When the number of tubes constitutes an odd multiple of three—such as 3, 6, 9, 15, or 21—they should be arranged in a clockwise pattern, as illustrated in the diagram below.

The 2x + 3x Balancing Method: When dealing with a configuration of 5, 7, 11, 13, 17, or 19 units, one may adhere to the principle of central symmetry by first balancing a group of three units, and then balancing the remaining two units; in this way, the combined result remains balanced overall.

Ultimately, the balancing of a centrifuge rotor is governed by the principle of symmetry: the relative masses of the two centrifuge tube cups situated on a single moment arm must remain identical. In practice, by simply loading the rotor wells sequentially—following a pattern such as 2 + 2 + 2... + 3—and ensuring that each set remains balanced, you can guarantee a foolproof and error-free operation. The illustrative diagram below demonstrates this principle with even greater clarity:

Only by mastering the proper balancing techniques for centrifuges can we ensure both experimental and personal safety, thereby preventing accidents before they occur.

Huatai Hehe Mini-Classroom:

Three Common Centrifugation Methods: Differential Centrifugation; Rate-Zonal Centrifugation; Isopycnic Centrifugation.

1. Differential Centrifugation

Differential centrifugation is frequently employed for the crude extraction of biochemical samples. It leverages the differences in sedimentation coefficients among various suspended particles within a centrifugal force field; under identical centrifugation conditions, particles of different types settle at varying rates. By progressively increasing the relative centrifugal force, particles of diverse sizes and shapes within a heterogeneous liquid suspension system are induced to settle in distinct layers.

The operational procedure typically involves separating the supernatant from the precipitate following the initial centrifugation step. The supernatant is then subjected to further centrifugation at a higher rotational speed to isolate a second fraction of precipitate. This iterative process continues—with the rotational speed being successively increased at each stage—to sequentially isolate the desired substances. Differential centrifugation offers relatively low resolution; particles with sedimentation coefficients falling within the same order of magnitude are difficult to separate effectively. Consequently, this technique is most commonly utilized for the preliminary, crude extraction of biochemical samples.

2. Rate-Zonal Centrifugation

Rate-zonal centrifugation is a form of incomplete sedimentation separation; its effectiveness is significantly influenced by the physical dimensions of the substances themselves. It is typically applied in situations where substances differ in size but share the same density. The technique operates on the principle that, under the influence of centrifugal force, particles to be separated will exhibit varying sedimentation velocities within a density gradient medium. Consequently, following centrifugation, particles with different sedimentation rates settle into distinct density gradient layers, forming separate sample zones and thereby achieving their mutual separation.

For instance, when isolating mononuclear cells from venous blood, the separation medium Ficoll causes all mononuclear cells (lymphocytes and monocytes) within the blood to settle into a single layer, allowing for their simultaneous extraction. In contrast, the separation medium Percoll resolves the lymphocytes and monocytes in the blood into two distinct gradient layers, enabling their separate extraction. During the centrifugation process—as well as during subsequent sampling—the gradient medium serves as both a supporting matrix and a stabilizer, preventing the resuspension of the separated, layered particles caused by mechanical vibrations.

When employing the rate-zonal centrifugation method, it is essential to strictly control the centrifugation duration. The time allotted must be sufficient to allow the various particles to form distinct zones within the gradient medium, yet not so prolonged as to cause any of the target particles to settle completely into a precipitate.

3. Isopycnic Zonal Centrifugation

Isopycnic zonal centrifugation is a centrifugation method applied to liquid dispersion systems containing particles with differing buoyant densities. Under the influence of a centrifugal force field, these particles either sediment downward or float upward along a density gradient until they reach a position where their density precisely matches that of the surrounding medium—known as the isopycnic point—thereby forming distinct zones.

The efficacy of isopycnic zonal centrifugation depends on the difference in buoyant density among the particles; the greater this density difference, the more effective the separation. This separation outcome is independent of the particles' size and shape, although these latter two factors do determine the rate and time required to reach equilibrium, as well as the width of the resulting zones.

Key characteristics of the isopycnic zonal centrifugation method include:

(1) The separation is dependent upon the density of the sample particles;

(2) The separation is independent of the sample particles' size and other parameters;

(3) Provided that the rotational speed and temperature remain constant, extending the centrifugation time will not alter the final zonal positions of these particles.

Now that you have gained an understanding of the centrifugation methods employed by centrifuges, do you have a general idea of how to go about selecting one? In this article:How to Choose the Right Centrifuge: A Guide to Size, Capacity, and Application

we provide a detailed guide on how to choose the right centrifuge—let's explore this topic together.

Centrifuge Balancing – Q&A

How to Balance a Centrifuge with an Odd Number of Tubes

To balance a centrifuge with an odd number of tubes, use dummy tubes filled with water to match sample weight and volume, creating an even, symmetric load. Distribute tubes evenly around the rotor to avoid vibration and damage.

How to Balance a Centrifuge with 5 Tubes

Balance 5 tubes by adding 1 dummy tube to make 6 total, then arrange them symmetrically at equal intervals around the rotor. All tubes must have identical weight and volume.

How to Balance a Centrifuge with 4 Tubes

Place 4 tubes directly opposite each other in symmetric pairs (e.g., 1&7, 2&8 in an 8-place rotor). Ensure equal volume and weight in all tubes for stable centrifugation.

How to Balance a Centrifuge with 2 Tubes

For 2 tubes, place them directly across from one another in the rotor. Confirm both tubes have the same liquid volume to maintain balance.

How to Balance a Centrifuge with 3 Tubes

Arrange 3 tubes evenly spaced 120° apart in a triangular pattern. All tubes must match in weight and volume for proper balance.

How to Balance 5 Tubes in a 12-Place Centrifuge

In a 12-place rotor, balance 5 tubes by using 1 dummy tube to create 6 balanced positions. Place tubes symmetrically in pairs and one single position with its dummy opposite.

How to Balance a Swinging Bucket Centrifuge

Balance a swinging bucket centrifuge by loading opposite buckets with equal-weight tubes. Never leave one bucket loaded while its pair is empty; use dummy tubes if necessary.

Centrifuge Balance Chart for 24-Place Rotor

2 tubes: 1 & 13

4 tubes: 1 & 13, 2 & 14

6 tubes: 1 & 13, 2 & 14, 3 & 15

8 tubes: 1 & 13, 2 & 14, 3 & 15, 4 & 16

Odd tube counts: Add dummy tubes to reach an even symmetric number.

1.What is the Working Principle of theRotary Vane Vacuum Pump?

The vanes of the rotary vane pump divide the crescent-shaped space—enclosed by the rotor, the pump chamber, and the two end covers—into three distinct sections: A, B, and C.

As the rotor rotates in the direction indicated by the arrow, the volume of Section A—which is in communication with the intake port—gradually increases; this constitutes the intake process.

Conversely, the volume of Section C—which is in communication with the exhaust port—gradually decreases; this constitutes the exhaust process. The volume of the intermediate Section B also gradually decreases; this constitutes the compression process.

vacuum pump work diagram

As the volume of Chamber A gradually increases (i.e., expands), the gas pressure within it decreases; consequently, the external gas pressure at the pump's inlet exceeds the pressure inside Chamber A, thereby drawing the gas in.

When Chamber A becomes isolated from the intake port—specifically, as it rotates into the position of Chamber B—the gas begins to undergo compression; its volume gradually diminishes until it eventually establishes communication with the exhaust port.

Once the pressure of the compressed gas exceeds the exhaust pressure, the exhaust valve is forced open by the gas, allowing the gas to pass through the oil layer within the oil tank and be discharged into the atmosphere. Through the continuous operation of the pump, the objective of continuous gas extraction is achieved.

If the discharged gas is channeled through a gas passage into a subsequent stage (a low-vacuum stage)—where it is drawn in, further compressed by that stage, and then discharged into the atmosphere—the assembly constitutes a two-stage pump. In this configuration, the total compression ratio is distributed across both stages, thereby enhancing the ultimate vacuum level attainable.

The rotary vane vacuum pump is an oil-sealed mechanical vacuum pump and constitutes one of the most fundamental pieces of equipment for generating vacuum in vacuum technology.

Rotary vane vacuum pumps are capable of evacuating dry gases from sealed containers; when equipped with a gas ballast device, they can also evacuate a certain amount of condensable gases.

However, they are not suitable for evacuating gases with excessively high oxygen content, gases that are corrosive to metals, gases that chemically react with the pump oil, or gases containing particulate dust. These pumps are available in two configurations: single-stage rotary vane vacuum pumps and double-stage rotary vane vacuum pumps.

2. What is the Structural Description of the Rotary Vane Vacuum Pump?

The rotary vane vacuum pump is a positive-displacement pump. It operates by utilizing rotating vanes within the pump chamber to continuously draw in and compress gas, which is ultimately discharged through the exhaust port.

The pump primarily consists of a stator, a rotor, and vanes; the rotor is mounted eccentrically within the stator chamber. Two vanes are seated within slots in the rotor, with a vane spring positioned between them. The inlet and exhaust ports located on the stator are partitioned into two distinct sections by the rotor and the vanes.

As the rotor rotates within the stator chamber, the vanes—driven by the combined forces of spring tension and centrifugal force—slide with their tips pressed tightly against the inner wall of the pump chamber. This action periodically expands the chamber volume on the inlet side to draw in gas, while simultaneously and gradually reducing the volume on the exhaust side to compress the already-ingested gas. The compressed gas is then expelled through the exhaust port, thereby achieving the objective of vacuum evacuation.

3. What are the Features and Applications of the Rotary Vane Vacuum Pump?

1) Features:

The vacuum pump's inlet port is fitted with a coarse filter featuring a metal wire mesh, designed to prevent solid foreign particles from being drawn into the pump chamber. The oil separator houses an exhaust filter that ensures highly efficient separation of oil from gas.

Upon pump shutdown, an inlet valve—integrated into the inlet port—isolates the pump from the system being evacuated, thereby preventing oil from back-flowing into the system. The pump is air-cooled. All models in the XD series of rotary vane vacuum pumps are driven by a directly coupled electric motor via a flexible coupling.

2) Applications:

a. The vacuum pump is suitable for creating a vacuum within closed systems. Typical applications include vacuum packaging, vacuum forming, and vacuum suction operations. b. Inlet Pressure Range: 100 Pa – 100.000 Pa. If operated outside this range, oil mist will be generated at the vacuum pump's exhaust port. The ambient operating temperature and the temperature of the intake gas for the XD-series rotary vane vacuum pump must be within the range of 5°C to 40°C.

c. The vacuum pump is not designed to pump water or other liquids. It must not be used to pump explosive, flammable, highly oxygenated, or corrosive gases.

d. The standard-supplied motor is not explosion-proof; if explosion-proof capabilities or other special requirements are needed, the motor must comply with the relevant standards.

4. How to Operate Rotary Vane Vacuum Pumps?

Before starting, verify that the cooling water supply for water-cooled pumps is connected. When the ambient temperature is low, manually rotate the pulley to ensure that the oil within the pump chamber drains back into the oil reservoir.

Next, press the motor start button to energize the unit. Pay close attention to ensure that the power supply polarity is not reversed and that the pump is rotating in the correct direction.

Check that the oil level in the vacuum pump is near the oil sight glass mark. When opening the valve to connect the pump to the system being evacuated, do not open it too rapidly, as this may cause excessive oil ejection. During operation, listen for any abnormal noises or mechanical impacts; also, monitor the pump's oil temperature. If localized overheating is detected, immediately shut down the pump to prevent seizing or excessive wear.

To shut down the pump, it is essential to vent the pump inlet to the atmosphere (most purchased units are equipped with an automatic vent valve). Disconnect the power supply first, and then shut off the cooling water supply.

5. What are the Performance Characteristics of Rotary Vane Vacuum Pumps?

A rotary vane vacuum pump is a device that achieves evacuation by utilizing vanes to periodically vary the working volume of the pump chamber. When a working fluid is employed for lubrication—filling the pump chamber's dead spaces and sealing the exhaust valve from the atmosphere—the pump exhibits the following performance characteristics:

a. Compact size, lightweight construction, and low noise levels;

b. Equipped with a gas ballast valve, enabling the evacuation of small quantities of water vapor;

c. Capable of achieving a high ultimate vacuum level;

d. Features an internal forced-oil circulation system, ensuring thorough lubrication and reliable performance;

e. Incorporates a dual-redundancy automatic anti-suckback mechanism to prevent oil backflow;

f. Capable of continuous operation even when the inlet pressure is maintained at 1.33 × 10 Pa;

g. Leak-free and splash-free operation that does not contaminate the working environment; the exhaust port is fitted with a dedicated oil mist collector;

h. Can be fitted with small-bore adapter fittings and international-standard KF flanges.

6. What are the Operational Specifications for Rotary Vane Vacuum Pumps?

Pumping Speed: 4–100 L/s (Liters/second)

Ultimate Pressure: ≤ 6 × 10 ⁻ ² Pa (Pascals)

Ultimate Vacuum: ≤ 1.3 Pa (Pascals)

Gas Type: Clean, dry air at ambient temperature, free from other mixtures. The pump must not be used to evacuate air containing dust particles or moisture.

Operational Requirements: When the inlet pressure exceeds 6500 Pa, the duration of continuous operation must not exceed 3 minutes; failure to observe this limit may result in oil ejection and subsequent damage to the pump. Under inlet pressure conditions of less than 1330 Pa, the pump is permitted to operate continuously for extended periods.

Ambient Temperature: Vacuum pumps are generally intended for use in environments with an ambient temperature of no less than 5°C and a relative humidity of no more than 90%.

7. What are the Precautions for Operating Rotary Vane Vacuum Pumps?

The rotor of a rotary vane vacuum pump is mounted eccentrically within the pump housing, positioned in close proximity to the fixed inner surface of the housing. Two (or more) vanes are fitted within the slots of the rotor.

As the rotor rotates, the vanes slide reciprocally along their radial slots while maintaining constant contact with the inner wall of the pump housing. These vanes rotate in unison with the rotor, effectively dividing the vacuum pump chamber into several compartments of varying volume. The following precautions should be observed when operating a rotary vane vacuum pump:

1) Check the oil level; ideally, the oil should be filled to the center of the oil sight glass when the pump is at rest. If the level is too low, the oil will fail to provide an effective seal for the exhaust valve, thereby compromising the achievable vacuum level. Conversely, if the level is too high, oil may be ejected from the pump when starting up under atmospheric pressure.

It is normal for the oil level to rise slightly during operation. Use only the specified grade of clean vacuum pump oil, adding it through the oil fill port. Ensure the oil fill plug is securely tightened after refilling. It is advisable to filter the oil prior to use to prevent foreign particles from entering and clogging the oil passages.

2) The pump can be started directly under atmospheric pressure or at any intermediate vacuum level. If an electromagnetic valve is installed at the pump inlet, it should be actuated simultaneously with the pump.

3) If the ambient temperature is excessively high, the oil temperature will rise, leading to a decrease in viscosity and an increase in saturated vapor pressure. This may result in a degradation of the ultimate vacuum level—particularly when measured using a thermocouple gauge (which indicates total pressure). The ultimate vacuum performance can be improved by enhancing ventilation and heat dissipation, or by utilizing a vacuum pump oil with superior thermal properties.

4) When verifying the ultimate vacuum performance of the pump, a compression-type mercury vacuum gauge should be used as the standard reference. Provided that the gauge has been thoroughly pre-evacuated and calibrated, and the pump temperature has stabilized, connecting the gauge directly to the pump inlet should allow the system to reach its ultimate vacuum level within 30 minutes of operation.

Readings obtained from total pressure gauges (such as thermocouple gauges) are subject to variables related to the pump oil, the gauge itself, and potential sensor errors; consequently, these readings may sometimes exhibit significant discrepancies and should be treated as reference values only. 5) If the relative humidity is high, or if the gas being evacuated contains a significant amount of condensable vapor, it is advisable to open the gas ballast valve after connecting the pump to the vessel being evacuated. Allow the pump to run for 20 to 40 minutes, then close the gas ballast valve. Before shutting down the pump, the gas ballast valve may be opened to allow the pump to run under no-load conditions for 30 minutes; this helps extend the service life of the pump oil.

8. What is the Operation and Maintenance of Rotary Vane Vacuum Pumps?

Before starting, verify that the cooling water supply for water-cooled pumps is connected. When the ambient temperature is low, manually rotate the pulley to ensure that the oil within the pump chamber drains back into the oil reservoir. Then, press the motor start button to apply power; pay close attention to ensure that the power supply polarity is not reversed and that the pump is rotating in the correct direction.

**Precautions During Pump Operation**

Check that the oil level is near the indicator mark on the oil sight glass. When opening the valve connecting the pump to the system being evacuated, do not open it too rapidly, as this may cause a sudden surge of gas that results in significant oil ejection. During operation, listen for any abnormal noises or knocking sounds; also, monitor the pump oil temperature. If localized overheating is detected, stop the pump immediately to prevent seizing or excessive wear.

**Precautions During Pump Shutdown**

When shutting down the pump, it is essential to vent the pump inlet to atmospheric pressure (most purchased pump units are equipped with an automatic air release valve). Disconnect the electrical power supply first, and then shut off the cooling water supply.

**Pump Maintenance and Care**

Do not mix different grades or brands of pump oil. Establish a reasonable oil change schedule based on the specific operating conditions. If the pump is removed from the system, seal the pump inlet to prevent dirt or foreign objects from entering the pump chamber. During operation, ensure that the pump is maintained within the specified environmental conditions.

9. How to Repair Rotary Vane Pumps?

Common faults associated with rotary vane vacuum pumps fall into the following categories:

1) Reduced vacuum level (failure to reach the required vacuum).

2) The pump fails to operate normally, or becomes "seized" (stuck).

3) Excessive noise or abnormal sounds occur during operation.

4) Poor sealing of the pump body—resulting in oil leakage.

5) Upon startup, significant amounts of oil droplets or oil mist are ejected, causing environmental contamination.

6) Difficulty in starting the pump.

Table 1 lists the common faults encountered in rotary vane mechanical vacuum pumps, their probable causes, and the corresponding troubleshooting and repair methods.

Table 1: Common Faults and Troubleshooting Methods for Rotary Vane Mechanical Vacuum Pumps

10. What is the Overhaul of Rotary Vane Pumps?

Rotary vane pumps require a major overhaul after operating for an extended period (typically 2.500 hours). During an overhaul, all components must be disassembled and cleaned; ideally, a specialized cleaning fluid designed for metal mechanical parts should be used for this purpose. Any worn components discovered during the cleaning process must be replaced.

**Disassembly Procedure for Pump Overhaul**

Disconnect the power supply and remove the pump from the equipment. Separate the vacuum pump body from the motor (alternatively, remove the drive belt, pulley, and key). Open the water drain plug to completely drain the cooling water. Open the oil drain plug and rotate the pulley to drain the vacuum pump oil. Remove the end cover of the low-vacuum chamber. Remove the sealing ring and extract the locating pins. Remove the low-vacuum rotor and vanes; when pulling out the rotor, take care to hold down the vanes with your hand to prevent the springs from ejecting and damaging the vanes. Using the same method described above, remove the high-vacuum end cover and extract the corresponding rotor and vanes.

**Pump Reassembly Procedure and Precautions**

To ensure the correct clearance at the tangent point between the rotor and the pump chamber, the pump should be positioned with the exhaust port facing downward. This allows the rotor's own weight to press it firmly against the pump chamber wall once installed, thereby facilitating automatic alignment and guaranteeing the proper tangent-point clearance.

The specific procedure is as follows: Insert the springs into the vanes, then insert the vanes into the rotor slots; press down on the vanes manually a few times to ensure they move freely without resistance. Install the high-vacuum and low-vacuum rotors into their respective pump chambers and connect the rotor shaft. Install the end covers, pulley, drive belt, and exhaust valve. Install the oil sight glass, fill the pump with oil, and then perform a test run to check for proper operation.

The clearance tolerances between various components during the assembly of a rotary vane pump ara critical. For domestically manufactured vacuum pumps, the appropriate assembly clearances can typically be selected based on the values provided in Table 2.

FAQ – Frequently Asked Questions About Vacuum Pumps

Q: Why does my vacuum pump sometimes struggle to reach the desired vacuum level?

A: This can happen if seals are a bit worn or if the pump oil needs changing. We recommend checking the condition of the seals, keeping the pump oil clean, and making sure there’s no blockage inside the pump.

Q: The vacuum pump sounds quite noisy when running. What should I do?

A: Noise usually comes from insufficient lubrication or bearings needing some attention. You could check the lubrication oil and, if necessary, consider replacing the bearings to reduce the noise.

Q: Is it normal for the vacuum pump to get warm or hot sometimes?

A: A little warmth is normal, but if it feels too hot, it might mean the cooling conditions aren’t ideal. Try checking the temperature and flow of the cooling water and ensure good ventilation around the pump.

Q: What common issues should I watch out for with mechanical pumps?

A: Oil contamination is quite common, especially if water vapor gets in, as that affects performance. Keeping the oil clean, checking belt tension, and monitoring oil level regularly can help prevent problems.

Q: How can I avoid backstreaming in diffusion pumps?

A: It’s best to avoid running the pump cold for long periods and to keep the cooling water flowing well. Using a cold trap can also greatly reduce the risk of oil backstreaming.

Q: What maintenance tips would you suggest for daily vacuum pump care?

A: We recommend regularly checking the oil level and uuality, maintaining proper operating temperature, and replacing worn parts promptly. These steps will help your pump run smootlly. If you’re looking for pumps designed with easy maintenance in mind, Huatai Hehe (Beijing) vacuum pumps are a good option.

Q: Are there any safety tips I should keep in mind when using a vacuum pump?

A: Try to avoid dry running or overloading the pump, and following the operating guidelines is very important. Regular safety checks will also help keep the equipment running safely and reliably.

Introduction to ELISA Reader Principles

In the vast world of life science research, ELISA readers (microplate readers) are not only indispensable partners in completing experiments, but also core engines driving research and quality control. From basic absorption detection to complex fluorescence luminescence applications, correctly selecting an ELISA reader is not only crucial for data reliability, but also a strategic decision for improving research efficiency and ensuring production stability.

So, faced with a dazzling array of instrument models and complex application scenarios, how do we make an informed choice? This article will guide you from principles to selection, taking you through the process!

01 Absorption

Principle: A beam of monochromatic light passes through a sample, part of which is absorbed, and part is transmitted. Absorbance is the amount of light absorbed by the sample.

Applications: ELISA, nucleic acid/protein quantification, etc.

Recommended plate type: Transparent plate or UV plate.

02 Luminescence

Principle: Light is generated through a chemical reaction (such as firefly bioluminescence), without the need for external light source excitation.

Applications: Reporter gene detection, ATP analysis, immunoluminescence, etc.

Recommended Plate Type: White plate or transparent plate with white border—helps reflect light signals and improve sensitivity.

03 Fluorescence

Principle: Specific wavelength light excites fluorescent groups, causing them to emit longer wavelength light.

Applications: Cell activity, gene expression, fluorescence immunoassay.

Recommended Plate Type: Black plate or transparent plate with black border—reduces background interference and inter-well crosstalk.

Advanced Fluorescence Detection Techniques

01 Fluorescence Polarization (FP)

Principle: Detects the strength of the interaction by analyzing the change in the rotational velocity of the fluorescently labeled molecule before and after binding to a macromolecule. After binding, the molecule becomes larger, and the polarized light signal is enhanced.

Applications: Receptor-ligand interactions, kinase activity, competitive immunoassay.

02 Time-Resolved Fluorescence (TRF)

Principle: Utilizes the long fluorescence lifetime of lanthanides to delay detection and avoid short-lived background fluorescence.

Applications: GPCR research, kinase detection, biomarker analysis, drug screening.

03 Alpha:

Principle: Utilizes the diffusion of singlet oxygen to trigger luminescence between closely spaced microbeads, detecting biomolecular interactions.

Applications: Protein-protein interactions (PPI), GPCR signaling, epigenetic screening.

04 Fluorescence Resonance Energy Transfer (FRET)

Principle: Due to the overlap between the donor's emission spectrum and the acceptor's absorption spectrum, when the donor and acceptor are very close, the donor is excited and transfers energy to the acceptor, causing the acceptor to emit fluorescence at its characteristic wavelength.

Applications: Studying protein-protein and protein-nucleic acid interactions, protein folding, etc.

05 BRET (Bioluminescence Resonance Energy Transfer)

Principle: Similar to FRET, but the donor is a bioluminescent protein, requiring no excitation light and exhibiting extremely low background.

Applications: Interaction studies, acceptor activation analysis, etc.

ELISA ReaderSelection

When selecting an ELISA reader, please be sure to clarify:

Core Application Type (Is it for high-end interactive research? Or routine quantitative analysis?)

Future Expandability (Will it be expanded to include luminescence, fluorescence, etc. detection?)

Detection Unit

The energy difference before and after light passes through the analyte is the energy absorbed by the analyte. At a specific wavelength, the concentration of the same analyte is quantitatively related to the absorbed energy.

The detection unit is expressed as OD value. OD is an abbreviation for optical density, representing the light density absorbed by the analyte. OD = Log(1/trans), where trans is the transmittance of the analyte. According to the Bouger-Amber-T-Beer rule, the OD value is related to the light intensity as follows:

E = OD = log10/1. where E represents the absorbed light density, 10 is the light intensity before the analyte, and 1 is the light intensity after the analyte.

The OD value is calculated using the following formula:

E=OD=C×D×E

C is the concentration of the analyte

D is the thickness of the analyte

E is the molar factor

Each substance has a specific wavelength at which it absorbs the most light energy. Choosing other wavelengths will result in inaccurate detection results. Therefore, when measuring analytes, we select a specific wavelength for detection, called the measurement wavelength.

However, each substance also exhibits a certain degree of non-specific absorption of light energy. To eliminate this non-specific absorption, we select a reference wavelength to eliminate this inaccuracy. At the reference wavelength, the absorption of light by the analyte is minimal. The difference between the absorbance values of the detection wavelength and the reference wavelength can eliminate non-specific absorption.

ELISA reader detection value calculation

The detector in the instrument receives the light energy transmitted through the analyte and converts it into a binary digital signal, with a maximum value of 4095. The instrument defines the transmittance value as 0% in the absence of a light source and 99.9% in the absence of analytes. In actual testing, the transmittance of the analyte is between 0% and 99.9%. The transmittance is calculated as follows:

T = (Meas - Min) / (Max - Min)

Where T is the transmittance, Meas is the binary value of the detected sample, Min is the binary value detected at 0%, and Max is the binary value detected at 99.9%. For example:

Max = 3600. Mn = 20. Meas = 30

T = (30 - 20) / (3600 - 20) = 0.0028

OD = log(1/T) = log(1/0.0028) = 2.552

Centering of the Microplate Reader

The instrument automatically centers the microplate wells. Centering eliminates inaccuracies caused by uneven thickness at the bottom of the wells. When performing tests on each ELISA reader, the instrument actually measures 35 points, and the average of the five middle points is taken as the OD value of that well.

Reference Channel for Light Source

The reference channel is used to calibrate against the effects of voltage instability or bulb wear.

Applications and Other Notes of the ELISA Reader

Used for ELISA reagent assays, widely used in various laboratories, including clinical laboratories.

Quality Control

Quality control is a crucial factor in reagent testing. Please perform quality control according to the reagent instructions.

Blank Correction

Some kit instructions set the blank wells to air; most others use reagent settings. Please follow the kit instructions.

Interpretation of Test Results

Since many factors can affect test results, such as different ELISA plates and reagent volumes, OD values will vary. Therefore, only test results from reagents reacted on the same ELISA plate can be compared and analyzed. For clinical interpretation of results, please refer to the kit instructions.

Low-Speed Centrifuge: 300–6,000 rpm Speed Range, Ultracentrifuge Speed Reference, and Advantages

I. Classification of Centrifuges

Centrifuges use centrifugal force generated by high-speed rotation to automatically separate substances of different densities – heavier substances sink, and lighter substances float. From cells and viruses to proteins and nucleic acids, centrifuges play an indispensable role in scientific research, clinical applications, and testing.

Centrifuges come in a wide variety of types, from micro-centrifuges to floor-standing models, and from low-speed to ultra-speed centrifuges, each with its unique application. According to different classification criteria, centrifuges can be divided into several types:

1. Classified by Rotation Speed

　　Low-speed centrifuges: Rotation speed typically ranges from 4000-8000 rpm, centrifugal force range: 1000-10000g, suitable for separating coarse particle suspensions.

　　High-speed centrifuges: Rotation speed ranges from 10000-25000 rpm, centrifugal force range: 50000g, mainly used for separating emulsions and fine suspensions.

　　Ultra-speed centrifuges: Rotation speed ranges from 50000-150000 rpm, centrifugal force range: ≥505000g, suitable for separating ultra-fine particle suspensions and high-molecular colloid suspensions.

Ultra-speed centrifuges include a vacuum system. A cooling system is essential. They require significant space and are generally floor-standing models.

2. Classification by Capacity

　　Microcentrifuge (benchtop): Suitable for processing small volume samples (such as 2mL or less), commonly used for separating cell culture supernatants, micro-volume serum, and DNA/RNA extraction.

Medium-throughput centrifuge (benchtop): Suitable for processing medium-volume samples, widely used in the separation of cell and tissue samples.

Large-capacity centrifuge (benchtop and floor-standing): Suitable for processing large-volume samples, commonly used in large-scale experiments such as blood separation and cell culture.

3. Classification by Temperature Control Function

Room temperature centrifuge: Suitable for samples that are not sensitive to temperature.

Refrigerated centrifuge (optional parameter): Equipped with a cooling system, suitable for processing temperature-sensitive samples, preventing sample denaturation due to temperature increase during centrifugation.

4. Classification by Structural Form

Benchtop centrifuge: Compact in size, suitable for laboratories with limited space.

Floor-standing centrifuge: Larger in size, suitable for laboratories that need to process large-volume samples.

Two concepts related to centrifugation and centrifuges: Separation Factor and Centrifugal Force

Centrifugal separation occurs through a centrifugal force field created by the high-speed rotation of materials within the centrifuge drum. The magnitude of the centrifugal force is directly proportional to the mass of the rotating material, the diameter of the drum, and the square of the rotational speed. Therefore, changing the rotational speed is the simplest and most effective way to change the centrifugal force.

In centrifuges, the separation factor (Fr) is typically used to measure the strength of the centrifugal force field. The separation factor is the ratio of the centrifugal force (Fc) experienced by the material in the centrifugal force field to its gravitational force (G) in the gravitational field. Clearly, the separation factor is also the ratio of centrifugal acceleration to gravitational acceleration.

The separation factor is a crucial indicator of centrifuge performance, reflecting its separation capacity. A higher Fr value indicates a greater separation driving force (Fc) and better separation effect. Therefore, for suspensions with small solid particles and high liquid viscosity, or emulsions with small density differences that are difficult to separate, centrifuges or separators with a higher separation factor should be used.

Increasing the rotational speed is more effective than increasing the drum diameter in improving the separation capacity of a centrifuge. However, the improvement in the separation factor (Fr) is limited. For a drum of a given diameter, the limiting value of Fr depends on the strength and density of the drum material. Currently, the commonly used Fr values for centrifuges are approximately between 300 and 1.000.000. Since gravity is negligible compared to centrifugal force, its influence can be completely ignored in centrifuge design. Therefore, the position of the centrifuge drum axis depends only on structural and operational convenience and can be placed anywhere in space.

Centrifuge Classification

Centrifuges are widely used in industrial production. To meet the needs of different production processes, there are many types and specifications of centrifuges, and many methods of classification exist. The main methods are as follows:

1. Classification by Continuity of Operation

① Intermittent Centrifuges. The processes of feeding, separation, and unloading are all performed intermittently. Some processes (feeding and unloading) often require slow speed or shutdown. Examples include three-legged and top-suspended centrifuges.

② Continuous operation centrifuges. All operations are performed automatically (continuously or intermittently) at full speed. Examples include horizontal scraper discharge centrifuges, piston pusher centrifuges, and screw discharge centrifuges.

2. By separation process:

① Filtration centrifuges. Examples include three-legged, top-suspended, and horizontal scraper discharge centrifuges.

② Sedimentation centrifuges. Examples include three-legged sedimentation centrifuges, scraper discharge sedimentation centrifuges, and screw discharge centrifuges.

③ Separators. Includes tubular separators, chamber separators, and disc separators.

3. By separation factor:

① Normal speed centrifuges. Separation factor Fr < 3500. with Fr = 400~1200 being the most common. These include both filtration and sedimentation types. These centrifuges are suitable for separating suspensions containing large or medium-sized solid particles and fibrous solids. They have a lower rotational speed but a larger drum diameter and a larger loading capacity.

② High-speed centrifuges. Separation factor Fr = 3500~50000. These centrifuges are typically sedimentation and separation types, suitable for separating thin suspensions and emulsions with a slurry-like or fine particle texture. Their drum diameter is generally small, and their rotational speed is high.

③ Ultra-high-speed centrifuges. Separation factor Fr > 50000. These are separation types. These centrifuges are suitable for separating difficult-to-separate, highly dispersed emulsions and colloidal solutions. Due to the very high rotational speed, the drum is often made into a long, thin tube.

4. Classification by Discharge Method

Centrifuges can be classified according to different discharge methods, including manual discharge, mechanical discharge (scraper discharge, piston pusher, screw discharge, etc.), and inertial discharge (centrifugal force discharge, vibration discharge, precession discharge, etc.).

In addition, they can also be classified according to the spatial position of the centrifuge drum axis, such as vertical and horizontal types.

There are many ways to classify centrifuges, but because centrifuges are a type of complex chemical machine, no single classification method can fully reflect the structural and operational characteristics of a specific type of centrifuge.

Centrifuge Selection

1. Selection Parameters

(1) Material Name and Characteristics (e.g., corrosiveness, abrasiveness, toxicity, etc.)

(2) Feed Rate

Feed rate refers to the amount of material the centrifuge is required to process per unit time during production. Process professionals should generally provide the minimum, normal, and maximum processing capacities. Common units are kg/h and m³/h.

(3) Suspension (Slurry) Temperature T

This refers to the temperature of the inlet medium at the centrifuge feed. The minimum, normal, and maximum temperatures of the inlet medium during operation should generally be provided. Common units are ℃.

(4) Material Density

Divided into solid density ρs, liquid density ρL, and suspension density ρ, etc., with units of kg/m³. These can be converted between each other.

(5) Particle Size

This refers to the average size of solid particles in a suspension. It can be expressed as the Stokes diameter (dst) or the median diameter (d50).

The Stokes diameter (dst) is determined by sedimentation in a gravitational or centrifugal field. dst is close to the actual size, and the sample can generally be obtained from a centrifuge manufacturer.

The median diameter (d50) refers to the particle size (mm) of 50% of the sample mass during sieving. It ensures that the mass fraction of particles larger and smaller than this diameter is equal. This method is the simplest, but has a large error and cannot measure very fine particles.

(6) Suspension Solid Concentration (φ)

The suspension solid concentration refers to the content of solid particles in the suspension. It is generally expressed as a mass fraction, that is, the proportion of the mass of solid particles in a unit mass of suspension. It can also be expressed as a volume fraction or the mass of solid particles contained in a unit volume of suspension, such as g/mL or g/L.

(7) Viscosity

Viscosity is divided into liquid viscosity (γf) and suspension viscosity (γ). Kinematic viscosity is commonly used and is measured in mm²/s (1 mm²/s = 1 cSt). Other types include dynamic viscosity and Engler viscosity.

2. Performance Indicators

(1) Production Capacity [Q]

This refers to the amount of material processed by a single centrifuge per unit time. For dehydration processes, the production capacity is generally measured by the amount of filter residue produced. For clarification processes, the production capacity is generally measured by the amount of filtrate produced. Units are m³/h and t/h.

(2) Separation Factor

The ratio of centrifugal acceleration to gravitational acceleration generated during centrifuge operation is called the separation factor.

The higher the separation factor Fr, the greater the centrifugal force on the material, and the better the separation effect. For small particles and difficult-to-separate suspensions with high liquid viscosity, centrifuges with a high separation factor are required. The separation factor range of industrial centrifuges is shown in the table of types and performance characteristics above.

The separation factor Fr is directly proportional to the drum radius of the centrifuge and the square of the drum speed. Therefore, the way to improve the separation factor of a centrifuge is to increase the drum radius and the drum speed, and increasing the drum speed is much more effective than increasing the drum radius. Therefore, centrifuges with high separation factors, such as disc centrifuges and tubular centrifuges, generally use small-diameter, high-speed models.

(3) Speed

The rated speed of a centrifuge refers to the allowable drum speed for centrifugal separation, measured in r/min.

(4) Shaft Power

Shaft power refers to the power transmitted from the drive motor to the main shaft of the centrifuge under given operating conditions, measured in kW.

Basic Selection Principles

The principles for centrifuge selection are related to its application, and are described below. (1) Selection Principles for Dehydration Processes

① When the solid concentration in the suspension is high, the particles are rigid or crystalline, and the particle size is large, a filter centrifuge can be used. If particle crushing is permissible, a horizontal scraper discharge centrifuge can be used; if particle crushing is not permissible, a horizontal piston pusher centrifuge or a centrifugal discharge centrifuge can be used.

② When the solid concentration in the suspension is low, the particle size is very fine, or the particles are amorphous mycelia, a filter centrifuge is not suitable because the particle size is too fine, resulting in significant material leakage from the filter screen. If a finer filter screen is used, the dehydration performance will decrease, and amorphous mycelia and oily solid particles will clog the filter screen. In this case, a sedimentation centrifuge, such as a screw discharge sedimentation centrifuge or a three-legged sedimentation centrifuge, should be used. If the particle size is very uneven, coarse particles can be filtered out first using a sieve, and then dehydration can be performed using a centrifuge. ③ When the density difference between the solid and liquid phases in the suspension is very small, and the particle size is above 0.01 mm, a filter centrifuge can be used. For large-scale processing, a continuous filter centrifuge can be used.

(2) Selection Principles for Clarification Processes

① When there is a large amount of liquid phase and a small amount of solid phase with very small solid particle size (below 10 μm), or amorphous mycelium, a screw discharge sedimentation centrifuge, disc separator, or tubular separator can be used. When the solid content is less than 1% and the particle size is less than 5 μm, a disc manual slag discharge separator or a tubular manual slag discharge separator can be used. When the solid content is less than 3% and the particle size is less than 5 μm, a disc piston slag discharge separator can be used.

② A tubular separator can separate fine particles of about 0.5 μm, and the resulting clarified liquid has a high clarity. However, the single-machine processing capacity is small, and the solid residue after separation adheres tightly to the inner wall of the drum, requiring disassembly for manual cleaning. It cannot be used for continuous production.

③ The disc piston slag separator can separate fine particles of about 0.5μm, producing a highly clear clarified liquid. After separation, the solid slag deposits on the inner wall of the drum. When a certain amount is accumulated, the machine can automatically open the piston to partially discharge the slag while continuously feeding. Because the piston opens instantaneously during operation, the solid slag cannot be completely discharged. Therefore, after a certain operating cycle, feeding should be stopped, and the piston should remain open for a longer period to completely discharge the solid slag.

(3) Selection Principles for Concentration Processes

The concentration process enriches the small amount of solid phase in the suspension.

① For materials with a large density difference between the solid and liquid phases, a hydrocyclone separator can be used.

② For materials with a small density difference between the solid and liquid phases, a disc nozzle slag separator can be used.

③ The screw discharge sedimentation centrifuge is also commonly used in the concentration process. Because it lacks a filter screen and nozzles, it does not cause material blockage. The moisture content of the discharge from the screw discharge sedimentation centrifuge is lower than that of the disc nozzle slag separator.

(4) Selection Principles for Grading Processes

① Generally, a screw discharge sedimentation centrifuge can be used. Based on the density difference between the solid and liquid phases and the particle size dk, a suitable separation factor and slip are selected. Particles larger than dk settle and are discharged from the solid phase, while particles smaller than dk remain in the liquid phase and are discharged with it, thus achieving particle grading. To prevent particles smaller than dk from being carried away by larger particles during sedimentation, appropriate speed, slip, and the position of the feed pipe inserted into the centrifuge's screw conveyor inner cylinder must be adjusted.

② If the throughput is very small, a three-legged sedimentation centrifuge can be used. Adjusting the appropriate separation factor allows for particle grading.

(5) Selection Principles for Liquid-Liquid and Liquid-Liquid-Solid Separation

Liquid-liquid and liquid-liquid-solid separation refers to the separation of two or three immiscible materials. The principle of separation is based on density differences. Examples include oil-water separation in edible oils, and the separation and purification of oil, water, and solids in fuel oils and lubricating oils.

① For small-scale liquid-liquid and liquid-liquid-solid separation, tubular separators can be used; for large-scale separation, disc-type manual slag discharge separators or piston slag discharge separators can be used.

② Due to the different contents of the liquid and liquid phases (e.g., more light phase A and less heavy phase B; or less light phase A and more heavy phase B), adjustment is required using regulating rings in both tubular and disc separators.

III. Operating Procedures and Precautions for Ultracentrifuges

1. Centrifuge Operating Procedures

1). Connect the power supply and open the centrifuge lid; assemble the centrifuge tubes as required.

2). Install the centrifuge rotor as required; close the centrifuge lid.

3). Input centrifugation data and program the centrifugation process.

4). Evacuate the chamber and start the program.

5). After the program ends, release the vacuum; open the centrifuge lid and remove the rotor.

6). Remove the centrifuge tubes and perform analysis.

2. Precautions for Using Ultracentrifuges

1) The centrifuge rotor and sleeves must correspond to each other, and the matching centrifuge tubes must be used. This ensures the compatibility of the rotor and centrifuge tubes, avoiding operational problems or safety risks due to incompatibility.

2) Balancing is crucial; the mass difference should not exceed 0.2g. Imbalanced weight distribution can cause uneven force on the rotor shaft, which may damage the centrifuge or cause safety accidents. When the centrifugal speed reaches 10,000-50,000 rpm, if there is a 1-gram difference between symmetrical tubes and the rotor radius is 5 cm, the centrifugal force formula is F = m × RCF. Looking up the table, at 10,000 rpm, RCF = 6000, so F = 1 × 6000 = 6 kg. At 50,000 rpm, RCF = 150,000, so F = 1 × 150,000 = 150 kg. This imbalance can cause a force of 6-150 kg, which is very damaging to the centrifuge and will at least shorten its lifespan.

3) After setting the centrifugation conditions, evacuate the chamber before starting centrifugation. This step helps improve centrifugation efficiency and ensure the accuracy of experimental results.

4) After use, return the rotor to the 4°C refrigerator before defrosting. This helps maintain the centrifuge's performance and extend its lifespan.

5) Avoid over-speed centrifugation, ensuring that the maximum speed and centrifugal force limits of the centrifuge are not exceeded to prevent equipment damage or sample loss.

6) During ultracentrifugation, the centrifuge tubes must be filled with liquid. Because vacuum is required during ultracentrifugation, only filling the tubes completely will prevent deformation.

If the centrifuge tube lid has poor sealing, the liquid cannot be completely filled (for high-speed centrifugation using an angle rotor) to prevent spillage. Consequences of spillage: contamination of the rotor and centrifuge chamber, affecting the normal operation of the sensors.

7) When using an angle rotor, remember to cover the rotor lid. If not covered, a large vortex resistance and frictional heating will be generated in the centrifuge chamber, which adds an extra burden to the centrifuge's motor and refrigeration unit, affecting the centrifuge's lifespan.

III. Classification of Ultracentrifuge Tubes

1. Quick-Seal Tubes

Quick-Seal tubes can be used with fixed-angle rotors, swing-out rotors, vertical rotors, and near-vertical rotors. These single-use tubes require heat sealing after sample loading. Quick-Seal tubes are suitable for samples that are radioactive, pathogenic, or otherwise hazardous.

1. Quick-Seal tubes are made of polypropylene (PP) and ultra-clean (UC) materials.

2. Based on the top structure, Quick-Seal tubes are divided into dome-top and bell-top types.

3. Based on the bottom structure, they are divided into round-bottom and conical-bottom types.

2. Optiseal Tubes

Optiseal tubes are single-use centrifuge tubes specifically designed for certain rotors, used with fixed-angle rotors, swing-out rotors, vertical rotors, and near-vertical rotors, and are available in dome-top and bell-top types.

Optiseal tubes come with a plastic sealing plug, allowing for convenient and quick use without tools or heating. During centrifugation, a spacer is required to seal and support the top of the tube. The spacer ensures the Optiseal tube is properly sealed.

3. Open-Top Tubes

Open-top tubes are divided into thin-wall and thick-wall types and can be used with fixed-angle and swing-out rotors. When using open-top tubes with fixed-angle rotors, a tube cap and capping tool are required, as indicated in the rotor manual.

1. Thin-walled open-top tubes are for single use only, and are made of polypropylene (PP) or ultra-clean (UC) materials.

When using a horizontal rotor, the sample should be filled to approximately 2-3 mm from the top of the tube to support the centrifuge tube. A cap is usually required when using an angle rotor.

2. Thick-walled open-top tubes are made of polypropylene (PP) and polycarbonate (PC) and are reusable.

4. Centrifuge Bottles

Centrifuge bottles are made of polycarbonate (PC) and polypropylene (PP). They can be used with fixed-angle rotors. Centrifuge bottles include a lid, inner plug, O-ring, and other lid components that seal the bottle. Lids are available in metal and plastic.

Note: When using ultracentrifuge tubes, it is essential to use the corresponding adapters, spacers, and other accessories. Please refer to the rotor manual for detailed information.

IV. Materials and Selection of Ultracentrifuge Tubes

For ultracentrifugation, the compatibility, sealing, and durability of the consumables are crucial for sample safety and centrifugation results. 1. Materials of Ultracentrifuge Tubes

Commonly used ultracentrifuge consumables are mainly made of plastic materials, such as polypropylene (PP), polycarbonate (PC), and polyethylene terephthalate (PET). They differ in their performance regarding centrifugal resistance, transparency, and resistance to high temperature and pressure.

2. Selection of Ultracentrifuge Tubes

Common types of ultracentrifuge consumables include: centrifuge bottles, thin-walled centrifuge tubes, thick-walled centrifuge tubes (wall thickness ≥1mm), heat-sealable tubes, and microcentrifuge tubes resistant to high RCF. The appropriate type should be selected based on the centrifugation method and rotor configuration.

1) For differential centrifugation experiments that require sample recovery by decanting, centrifuge bottles or thick-walled tubes are preferred for fixed-angle rotors, while thin-walled open tubes are recommended for swing-out rotors.

2) For density gradient centrifugation, due to varying subsequent sample recovery methods, and considering that most require piercing the tube wall, thin-walled open tubes or heat-sealable tubes are recommended.

3) For experiments requiring strict tube sealing, heat-sealable tubes are preferred.

4) Microcentrifuge tubes are only suitable for some small-volume rotors.

3. Number of Uses for Ultracentrifuge Tubes

Quick-seal tubes, OptiSeal tubes, ultra-clean tubes, and thin-walled open tubes are for single use only and are convenient for subsequent piercing and sampling in density gradient centrifugation. Thick-walled open tubes and centrifuge bottles can be reused, but it must be confirmed that the tubes or bottles have no cracks or deformation before use.

V. Sterilization and Cleaning Methods for Ultracentrifuge Tubes

Sterilization of Ultracentrifuge Tubes

1. Polypropylene (PP) Centrifuge Tubes

PP centrifuge tubes can be sterilized by high-temperature and high-pressure autoclaving.

Before autoclaving, place the centrifuge tubes vertically in a tube rack or beaker with the opening facing downwards. Avoid bundling or stacking to prevent pressure buildup.

Set the sterilization temperature and time to 121°C for 20-40 minutes. After sterilization, allow them to cool naturally to room temperature before use. To avoid deformation of the centrifuge tubes, drying is not recommended. If drying is necessary, the temperature should be kept below 40°C.

2. Polycarbonate (PC) and Ultra-Clean (UC) Centrifuge Tubes

High-temperature and high-pressure sterilization of PC centrifuge tubes will affect their lifespan, so cold sterilization is recommended.

For PC and UC centrifuge tubes, immerse them in 6-10% hydrogen peroxide or 5% sodium hypochlorite in a clean bench for 20-30 minutes.

After pouring out the hydrogen peroxide or sodium hypochlorite, rinse with sterile water several times. Finally, air-dry the treated centrifuge tubes before use.

3. Sterilization of Metal Tube Caps

All metal tube cap components can be sterilized by high-temperature and high-pressure autoclaving at 121°C for 30 minutes. The components need to be disassembled before sterilization.

4. Sterilization of OptiSeal Finger-Seal Tube Plugs

70% alcohol and 6-10% hydrogen peroxide can be used for the sterilization of plastic plugs in finger-seal tubes, as well as other plastic components in tube caps.

2. Cleaning of Ultracentrifuge Tubes

For reusable centrifuge tubes, please note the following during cleaning:

1. When cleaning centrifuge tubes, centrifuge bottles, adapters, and other accessories, use a mild detergent, such as Solution 55 diluted 10 times with water, and clean with a soft brush.

2. Polycarbonate (PC) centrifuge tubes and bottles are susceptible to corrosion from alkaline solutions and detergents. Therefore, use a detergent with a pH less than 9, such as Solution 55, for cleaning.

Also, avoid using brushes with exposed metal to prevent scratching the PC centrifuge tubes and affecting their use.

3. Many centrifuge tubes are not resistant to alcohol, acetone, etc. Before cleaning centrifuge tubes with these solvents, please check their chemical resistance.

4. After cleaning, do not dry in an oven; air drying is required.

Centrifuges are essential pre-processing equipment in laboratories.Low-speed centrifuges, in particular, are widely used in clinical medicine, biochemistry, immunology, industry, food analysis, and other fields, and are a conventional instrument for centrifugal sedimentation in laboratories. They are suitable for sample centrifugation before experimental testing in hospital departments, biochemical analyzers, and immunoassays.

The following is a brief analysis of several application scenarios:

01. Medical:

Blood sample centrifugation:

Typically requires a speed of 3000 rpm for about 10 minutes;

Urine sample centrifugation:

Typically requires a speed of 1800 rpm for about 5 minutes;

Stool sample centrifugation:

Typically requires a speed of over 1000 rpm for about 10 minutes;

02. Beauty salons and dental hospitals:

PRP application:

Typically around 3000-3500 rpm, centrifugation time of about 5 minutes, performed twice or multiple times;

PRF application:

Typically around 2000-3000 rpm, centrifugation time of about 7 minutes, completed in a single centrifugation;

CGF application:

Typically consists of 3 or 4 steps of variable speed centrifugation;

03. Food analysis:

Sample centrifugation in vegetable or food pesticide residue testing:

Typically requires around 4000 rpm, centrifugation time of 5 minutes.

04. Biological laboratories:

Cell culture medium centrifugation:

Typically requires several hundred g-force (relative centrifugal force), and it is recommended to choose a low-speed horizontal rotor.

Precautions for use are as follows:

01. Installation:

The centrifuge must be installed on a solid, flat, and level surface, ensuring that all four feet of the centrifuge are in contact with the surface. Do not install the centrifuge on a sliding surface, as this may cause significant vibration.

The ideal ambient temperature is 20℃±5℃, and the ambient temperature should not exceed 30℃. Avoid direct sunlight on the centrifuge.

Ensure a 10cm gap on both sides of the centrifuge and a 30cm gap at the back to ensure proper air cooling.

There should be no heat sources or water leaks near the centrifuge, otherwise, it may cause the sample temperature to rise or the centrifuge to malfunction. Ensure a good ground connection and avoid touching power cords with wet hands to prevent electric shock.

02. Rotor Inspection:

Before use, check the rotor for corrosion or scratches. If any problems are found, stop using it. Do not use other incompatible rotor models on the main unit. Before use, ensure that the rotor is securely tightened to the spindle and that the lid is securely fixed to the rotor if a matching lid is available.

03. Sample Balancing:

Ensure that each sample centrifuge tube is weighed on a balance and check that the samples are symmetrically installed. Even a slight imbalance can lead to dangerous accidents. Common balancing methods are as follows:

04. What is the maximum capacity of the centrifuge tube?

It is recommended not to exceed 80% of the centrifuge tube's maximum capacity.

05. How is centrifugal force calculated?

RCF = 11.17 x (rpm/1000)² x R, the larger the radius, the greater the centrifugal force; the higher the speed, the greater the centrifugal force.

06. How to disinfect the centrifuge rotor?

Plastic rotors: If there is sample leakage, a neutral absorbent liquid can be used for cleaning and wiping, but UV disinfection should not be used, as it will make the material brittle and affect its lifespan;

Aluminum alloy rotors: Can withstand 121 degrees Celsius, high-temperature and high-pressure sterilization, and there is no limit to the number of sterilization cycles.

Introduction

A low-speed centrifuge is one of the most commonly used laboratory instruments, widely applied in clinical, research, and industrial laboratories. Compared with high-speed centrifuges, low-speed centrifuges focus on gentle separation, ease of operation, and sample integrity.
Below is a comprehensive Q&A guide explaining what a low-speed centrifuge is, how it differs from a high-speed centrifuge, its speed range, applications, and key advantages.

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Q1: What Is a Low-Speed Centrifuge?

A low-speed centrifuge is a laboratory centrifuge designed to separate samples at relatively low rotational speeds. It uses centrifugal force to separate components of a mixture based on density differences, typically for applications that do not require extreme centrifugal force.

Low-speed centrifuges are commonly used for:

• Blood sample separation

• Cell harvesting

• Urine and biological sample preparation

• Routine laboratory analysis

They are ideal for samples that are sensitive to high centrifugal stress.

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Q2: What Is the Difference Between a High-Speed Centrifuge and a Low-Speed Centrifuge?

The main differences between high-speed and low-speed centrifuges lie in their speed range, centrifugal force, and application scenarios.

Feature	Low-Speed Centrifuge	High-Speed Centrifuge
Maximum Speed	Typically up to 6,000 rpm	Usually 10,000 rpm or higher
Centrifugal Force	Low to moderate	Very high
Sample Type	Blood, cells, suspensions	Proteins, organelles, viruses
Sample Damage Risk	Low	Higher if not controlled
Cost & Maintenance	Lower	Higher

Low-speed centrifuges are preferred for routine laboratory work, while high-speed centrifuges are used for advanced biochemical and molecular research.

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Q3: What Is the Minimum Speed of a Centrifuge?

The minimum speed of a centrifuge depends on the model and design, but most low-speed centrifuges can operate at speeds as low as300–500 rpm.

Such low speeds are useful for:

• Gentle sedimentation

• Preventing cell rupture

• Handling fragile biological samples

Some advanced models allow precise speed adjustment to meet specific experimental requirements.

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Q4: What Is the Maximum Speed of Low-Speed Centrifugation?

The maximum speed of a low-speed centrifuge generally ranges between4,000 and 6,000 rpm, depending on rotor type and manufacturer specifications.

This speed range provides sufficient centrifugal force for:

• Plasma and serum separation

• Cell pelleting

• Routine clinical and laboratory workflows

Compared with high-speed centrifuges, low-speed centrifuges prioritize stability and sample safety over extreme force.

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Q5: What Are the Applications and Advantages of Low-Speed Centrifuges?

Applications

Low-speed centrifuges are widely used in:

• Clinical laboratories and hospitals

• Medical testing and diagnostics

• Biotechnology and pharmaceutical labs

• Educational and research institutions

• Food and environmental testing labs

Advantages

Key advantages of low-speed centrifuges include:

• Gentle separation, protecting delicate samples

• Simple operation, suitable for routine use

• Lower noise and vibration

• Cost-effective, with lower purchase and maintenance costs

• High reliabilityfor daily laboratory tasks

These benefits make low-speed centrifuges an essential tool for laboratories requiring efficiency and consistency.

Conclusion

Low-speed centrifuges play a critical role in routine laboratory operations, offering reliable separation at controlled speeds. With lower rotational speed, reduced sample damage, and broad application coverage, they are an ideal choice for clinical diagnostics, research labs, and industrial testing environments.

RPM vs RCF in Centrifugation: Master the Key Differences for Lab Success

If you’re a lab researcher, you’ve almost certainly been confused by RPM and RCF—the two core parameters on every centrifuge. Both are linked to centrifugal force, but they serve entirely different purposes, and mixing them up can ruin your experiments, waste samples, and even compromise results. In this guide, we’ll break down the critical differences between RPM and RCF, explain why both matter, and show you how to convert between them effortlessly.

What is RPM? (Revolutions Per Minute)

RPM stands for Revolutions Per Minute—it’s a direct measurement of how many full rotations a centrifuge rotor makes in one minute. For example, setting your centrifuge to 3000 RPM means the rotor spins exactly 3000 times every minute.

RPM is a machine-focused metric: it only tells you how fast the rotor is turning, with no consideration for the actual force acting on your samples. A critical caveat: the same RPM setting can produce drastically different centrifugal force depending on the rotor radius. A large rotor will generate far more force at 3000 RPM than a small one—this is why RPM alone is never enough to define your centrifugation conditions.

Centrifuges are categorized by their maximum RPM ranges:

- Low-speed centrifuges: As low as 300 RPM up to 6000 RPM, ideal for routine lab work like blood separation and cell harvesting ([learn more about low-speed centrifuge speed ranges and advantages]( https://www.huataihehe.com/fqashow_19.html )).

- High-speed centrifuges: 10,000 RPM to 25,000 RPM, used for separating proteins, organelles, and fine suspensions.

- Ultracentrifuges: 50,000 RPM to 150,000 RPM, for ultra-fine particle and high-molecular colloid separation, with specialized vacuum and cooling systems.

What is RCF? (Relative Centrifugal Force)

RCF, or Relative Centrifugal Force, is the sample-focused metric that truly measures centrifugation effectiveness. Expressed as a multiple of Earth’s gravitational force (×g, or g-force), it tells you exactly how much force your samples are subjected to—e.g., 5000×g means the centrifugal force is 5000 times the force of gravity.

Unlike RPM, RCF accounts for both rotor speed and rotor radius, making it the universal standard for centrifugation protocols. If two centrifuges are set to the same RCF, your samples will experience identical force—regardless of rotor size or machine model. This is why scientific papers and lab protocols always report results in RCF, not RPM: it ensures experimental reproducibility across different labs and equipment.

RCF is also referred to as g-force or ×g—these terms are interchangeable in centrifugation.

Core Differences Between RPM and RCF

The table below sums up the key distinctions to keep in mind:

Feature	RPM (Revolutions Per Minute)	RCF (Relative Centrifugal Force)
Definition	Rotor rotation speed per minute	Centrifugal force relative to Earth’s gravity
Focus	Machine performance	Sample experience
Factors Considered	Only rotation speed	Rotation speed + rotor radius
Reproducibility	Non-universal (varies by rotor)	Universal (consistent across equipment)
Use Case	Quick machine setting	Defining experimental conditions, reporting results
Unit	Revolutions/minute	×g (g-force)

How to Convert RPM to RCF (and Vice Versa)

If your centrifuge only displays RPM (common on older models), you can easily convert it to RCF using a simple mathematical formula—the same formula used for all lab centrifuges, including low-speed models ([master RCF conversion and rotor selection with our detailed guide]( https://www.huataihehe.com/fqashow_17.html )).

The Official RPM to RCF Conversion Formula

RCF = 1.118 × 10 ⁻⁵ × r × (RPM)²

Where:

- RCF = Relative Centrifugal Force (in ×g)

- r = rotor radius (the distance from the centrifuge shaft center to the sample in the tube, in centimeters (cm))

- RPM = Rotations Per Minute

- 1.118 × 10 ⁻⁵ = A constant to balance units for g-force calculation

A simplified version of the formula (easier for mental math/quick calculations) is also widely used:

g = (RPM / 1000)² × r × 11.18

Key Note on Rotor Radius

Rotor manufacturers typically provide three radius values: minimum, average, and maximum (measured from the shaft to the top, middle, and bottom of the centrifuge tube). For most routine experiments, use the average radius for the most accurate RCF calculation.

Modern centrifuges eliminate the need for manual conversion—they let you toggle directly between RPM and RCF on the control panel, a huge time-saver for lab work!

Why Getting RPM vs RCF Right Matters

Mixing up RPM and RCF isn’t just a minor mistake—it can have serious consequences for your experiments:

1. Ineffective separation: Too little RCF (even at high RPM with a small rotor) means particles won’t sediment properly; too much RCF can rupture fragile cells or denature proteins.

2. Non-reproducible results: Reporting RPM instead of RCF makes it impossible for other researchers to replicate your work with different centrifuges/rotors.

3. Sample waste: Failed separations force you to repeat experiments, wasting precious samples (e.g., biological fluids, purified proteins).

4. Equipment risk: While rare, incorrect settings can lead to unbalanced rotors—especially critical for high/ultra-speed centrifuges—causing vibration, damage, or safety hazards.

Frequently Asked Questions (FAQs)

Q: Are RCF and g-force the same thing?

A: Yes! RCF (Relative Centrifugal Force) is synonymous with g-force (×g) in centrifugation—they refer to the exact same measurement.

Q: What’s the difference between RCF and XG?

A: There is no difference. XG (or ×g) is just the numerical expression of RCF, representing the multiple of gravitational force. These terms are used interchangeably in lab protocols and centrifuge manuals.

Q: Do I need to convert RPM to RCF for low-speed centrifugation?

A: Yes—even low-speed centrifuges (300–6000 RPM) require accurate RCF for consistent results, especially for clinical work like blood/urine sample processing or PRP/PRF applications ([explorelow-speed centrifugeapplications and best practices]).

Q: How do I choose the right rotor for accurate RCF?

A: Rotor type (horizontal, angle, vertical) impacts both RCF and separation efficiency. Horizontal rotors are ideal for low-speed, high-capacity work, while angle rotors deliver higher RCF for faster separation ([learn rotor selection tips for low-speed centrifuges].

Final Takeaways

- RPM = how fast the rotor spins (machine speed, not force).

- RCF = how much force the sample feels (universal, reproducible, the gold standard for experiments).

- Always report and set experiments in RCF—convert RPM only if your centrifuge doesn’t have a direct RCF setting.

- For low-speed centrifuge mastery (the workhorse of most labs), dive into our detailed guides on [speed ranges and advantages]( https://www.huataihehe.com/fqashow_19.html ) and [practical usage, RCF conversion, and rotor types]( https://www.huataihehe.com/fqashow_17.html ).

By understanding the difference between RPM and RCF, you’ll ensure precise, reproducible centrifugation every time—saving time, samples, and avoiding costly experimental errors!

I. Working Principle of a low-speed centrifuge

The physical basis of sedimentation separation in alow-speed centrifugeis the effect of centrifugal force on the sample. When a centrifuge tube containing the sample is placed in the centrifuge, the centrifuge starts working, and the sample undergoes uniform circular motion, generating an outward centrifugal force. The larger the radius of rotation and the faster the rotation speed, the greater the centrifugal force, and the faster the particles settle. Because different particles have different masses, densities, sizes, and shapes, their sedimentation velocities differ in the same fixed centrifugal field.

II. Centrifugal Force and Relative Centrifugal Force

1. Centrifugal Force

F = mw²r (where F is the centrifugal force intensity, m is the effective mass of the sedimenting particles, W is the angular velocity of the centrifugal rotor in rad/s, and r is the centrifugal radius in cm, i.e., the distance from the center of the centrifuge shaft to the bottom of the test tube in a horizontal centrifuge, or the distance from the center of the test tube opening in a vertical centrifuge)

2. Relative Centrifugal Force (RCF)

Centrifugal force is usually expressed as relative centrifugal force (RCF), which is the ratio of the magnitude of the centrifugal force F to the Earth's gravitational force, measured in grams (g). RCF is a parameter only related to the centrifuge and has no direct relationship with the sample.

Relative centrifugal force (RCF) is the true standard for measuring centrifugation effectiveness because it directly reflects the magnitude of the centrifugal force exerted on the sample, thus determining the efficiency and speed of particle separation. Regardless of the size or model of the centrifuge rotor, as long as the RCF value is the same, the centrifugal force exerted on the sample is the same. This makes experimental conditions comparable between different laboratories and different models of centrifuges.

III. Rotational Speed (RPM)

RPM, short for Revolutions Per Minute, is a unit describing the pure rotational speed of a centrifuge rotor, indicating how many revolutions the rotor makes per unit time (one minute). For example, when a centrifuge displays a speed of 10.000 RPM, it means that its rotor rotates 10.000 times per minute.

It only describes the speed of the machine's rotor rotation. This parameter only reflects the rotor's rotational frequency.

IV. RPM to RCF Conversion

The conversion formula between RCF and RPM is as follows:

RCF = 1.118 × 10^(-5) × r × (RPM)^2

Or:

g = (RPM / 1000)^2 × r × 11.18

The meaning and units of each term in the formula:

RCF (g): Relative centrifugal force, unit is "g" (a multiple of the Earth's gravitational acceleration).

r: Centrifugal radius, unit is "cm". This refers to the effective radius of rotation from the rotor axis to the bottom of the centrifuge tube (or the center of the sample).

RPM: Revolutions per minute, unit is "revolutions per minute".

1.118 × 10^(-5): This is a constant used to balance units and express the result in "g".

V. Selection of Centrifuge Rotors

The rotor is an integral part of the centrifuge and can be divided into horizontal rotors and angle rotors, each with its own application range.

1. Horizontal Rotor

The basket of a horizontal rotor can swing horizontally at a 90° angle, allowing the sample precipitate to be located directly in the middle of the bottom of the tube. The advantage of these rotors is the availability of different adapter options, enabling high capacity and high flexibility.

Sample separation effect:

The sample precipitate is located in the middle of the tube bottom, rather than on the side of the tube wall as in a fixed-angle rotor. The advantage is that when the concentration of the sample to be separated is low, as long as the sample is concentrated as possible at the bottom of the tube, and then resuspended with a small volume of buffer, the sample concentration can be maximized. Additionally, gradient centrifugation also requires a horizontal rotor to form multiple horizontal gradient layers and ensure that the positions of each horizontal gradient are maintained after centrifugation.

Scenarios requiring a horizontal rotor:

① High sample throughput;

② Gradient centrifugation required;

③ Sample needs to be centrifuged to the middle of the tube bottom;

2. Angle Rotor

(1) Fixed-Angle Rotor

In a fixed-angle rotor, the sample tube is centrifuged at a fixed angle, and the sample usually precipitates on the tube wall. Unlike a horizontal rotor, a fixed-angle rotor does not have movable parts, and the rotor experiences less metal pressure. Therefore, a fixed-angle rotor can achieve higher relative centrifugal force and thus shorter centrifugation time (Eppendorf 5430 R can achieve a relative centrifugal force of up to 30.000 x g). The disadvantage is that the centrifugal throughput is limited (the maximum centrifugal throughput of the Eppendorf benchtop centrifuge is 6 x 250 mL, and the maximum centrifugal throughput of the floor-standing high-speed centrifuge is 6 x 1 L).

Sample Separation Performance

Most fixed-angle rotors achieve the tightest sample precipitate at a 45° angle. Fixed-angle rotors less than 45° result in a more dispersed sample precipitate area, potentially leading to resuspension of the precipitate during supernatant transfer and affecting separation performance.

Fixed-angle rotor is required:

① Requires greater relative centrifugal force for complete separation;

② Requires more compact particles;

③ Smaller sample volume;

(2) Vertical-angle rotor:

The centrifuge tube is placed vertically, with the centrifugal force direction parallel to the tube axis. The sample settles rapidly along the length of the centrifuge tube, resulting in the shortest sedimentation path among the three types of rotors. Advantages: Fastest separation speed, reduces sample diffusion, significantly improves separation precision, and is suitable for demanding ultracentrifugation experiments.

Scenarios requiring vertical angle rotors:

Primarily used in ultracentrifuges, enabling precise experiments such as the separation of subcellular components (e.g., mitochondria, chloroplasts) and rapid preparation via density gradient centrifugation. It is a key component for precise separation in scientific research.

Summary on rotor selection:

VI. Relationship between FCF (g-value), rpm, and r-value for different rotors

This can be read from the following two graphs:

Relative centrifugal force (FCF) nomogram for a high-speed rotor

To determine an unknown value in a particular column, use a ruler to arrange the known values in the other two columns, ensuring they fall at the intersection of the ruler and the third column. For example, at a rotor speed of 80.000 rpm and a rotation radius of 20 mm, the relative centrifugal force (FCF) is approximately 150.000 g.

To determine an unknown value in a column, use a ruler to arrange the known values in the other two columns, ensuring they fall at the intersection of the ruler and the third column. For example, when the rotor speed is 5000 rpm and the rotation radius is 40 mm, the relative centrifugal force (FCF) is approximately 1100 g.

Centrifuge usage and precautions

I. Classification of Centrifuges

(1) According to speed, centrifuges can be classified as: low-speed centrifuges, high-speed centrifuges, and ultra-high-speed centrifuges.

(2) According to capacity, centrifuges can be divided into: microcentrifuges (mini centrifuges or micro-centrifuges), small-capacity centrifuges, large-capacity centrifuges, and ultra-large-capacity centrifuges.

(3) According to whether or not they are refrigerated, centrifuges can be divided into: refrigerated centrifuges and ambient-temperature centrifuges.

II. Centrifuge Use

1. Preparation Before Start-up

Ensure the centrifuge is placed on a stable and firm surface and connected to the power supply.

Check that the rotor is installed correctly and securely.

Select the appropriate rotor and centrifuge tubes according to the experimental requirements, and ensure the caps of the centrifuge tubes are tightly closed.

Clean the centrifuge chamber of any debris to ensure that no foreign objects affect the centrifugation process.

2. Setting Parameters

Turn on the centrifuge power switch and set the rotation speed (RPM), time (minutes), and temperature (if applicable) according to the experimental requirements.

Confirm that the set parameters are within the centrifuge's allowable range to avoid overloading.

3. Loading Samples:

Place the centrifuge tubes symmetrically in the centrifuge chamber to ensure rotational balance.

Use specialized tools or gloves to load and unload centrifuge tubes and rotors to prevent hand injuries.

Close the centrifuge lid and ensure the locking mechanism is in place.

4. Start-up and Monitoring:

After confirming all settings are correct, press the "Start" button to start the centrifuge.

During centrifugation, carefully observe the centrifuge's operating status. If any abnormal sounds or vibrations are heard, stop the centrifuge immediately and check.

5. End-of-Life and Unloading:

The centrifuge will automatically stop after the preset time. Wait until the rotor has completely stopped rotating before opening the centrifuge lid.

III. Precautions

1. Balancing Issues

Starting a centrifuge without balancing can result in minor damage to the machine, or even serious injury or death!

Centrifuging at 1.000.000 x g results in 1 g of sample producing 1.000 kg. If this is accidentally ejected, it's equivalent to a high-speed bullet, extremely dangerous.

The principle of balancing is: the solutions in corresponding centrifuge tubes should have equal density and volume—meaning they have the same center of gravity during centrifugation.

For weight balancing, a precision balancing deviation of no more than 0.1g is generally required, while for routine applications, the deviation should generally not exceed 1g. The weight deviation must not exceed the range specified in the centrifuge instruction manual.

Avoid loading an odd number of centrifuge tubes into the rotor. When the rotor is only partially loaded, the tubes should be evenly distributed to ensure uniform load distribution across the rotor body. When there is an odd number of centrifuge tubes, the balancing tubes must be filled with a material of similar density; for example, water can be used for balancing bacteria from a culture medium.

(1) Balancing of 12-hole fixed angle rotor:

(2) Rotor Balancing

Not only must the symmetry of the centrifuge tubes within a single basket be considered, but the balance of the centrifuge tubes in the opposite basket must also be taken into account. In this case, two principles must be remembered during balancing:

When placing centrifuge tubes in a single basket, ensure that the basket's center of gravity is at its center point;

When placing centrifuge tubes in the opposite basket, use the placement position of the first basket as a reference, strictly adhering to the principle of rotor center point symmetry, and then place them in appropriate positions.

(3) Balancing odd numbers: If you find it troublesome to use a blank balancing tube (filled with water) for balancing, you can use the following method:

3x balancing method: When there are odd numbers of centrifuge tubes that are multiples of 3. such as 3. 6. 9. 15. 21:

The 2x balancing plus 3x balancing method: When there are 5. 7. 11. 13. 17. or 19 tubes, you can follow the principle of central symmetry, first keep 3 tubes in balance, and then keep the other 2 tubes in balance. This way, the result is still balanced.

2. Safety Issues

(1) Never open the centrifuge lid during centrifugation to prevent injury from flying objects.

(2) Centrifuge within the recommended speed range to prevent overexposure.

(3) For volatile, toxic, or corrosive samples, additional protective measures should be taken, and operations should be performed in a fume hood.

(4) Check the chemical resistance of all centrifuge tube materials. The material selection must be compatible with the experiment. Do not use counterfeit or substandard centrifuge tubes, or aged, deformed, or cracked centrifuge tubes.

(5) For refrigerated centrifuges: When the centrifuge is pre-cooled, the centrifuge lid must be closed. After centrifugation, remove the rotor and place it upside down on the lab bench, wipe off any remaining water in the chamber, and leave the centrifuge lid open. During pre-cooling, the rotor cap can be placed on the centrifuge platform or the lab bench. Never leave it loosely on the rotor, as it could fly off and cause an accident if the centrifuge is accidentally started!

(6) If the electric centrifuge makes noise or vibrates, immediately disconnect the power and troubleshoot the problem.

(7) After separation, turn off the centrifuge first. Only after the centrifuge has stopped rotating can you open the centrifuge cap and remove the sample. Do not force it to stop.