How Does a Centrifuge Work? Full Centrifuge Machine Guide

Why wait hours for gravity when you can get results in minutes? A laboratory centrifuge accelerates natural separation — turning an overnight wait into a three-minute spin.

This guide covers how centrifuge machines work, what separates results by density, how to operate and balance one safely, and which applications each centrifuge type is built for. Drucker Diagnostics has manufactured more clinical centrifuges than any other company; the principles here reflect what we’ve learned from millions of cycles in labs worldwide.

TLDR

• A centrifuge separates sample components by density using centrifugal force from rapid rotation.
• Denser particles move to the bottom of the tube; lighter components stay near the top.
• Clinical centrifuges process blood, urine, and serum in 3 to 15 minutes — replacing hours of gravity-based settling.
• RCF (G-force), not RPM, is the correct unit for comparing centrifuge protocols across machines.

What Is a Centrifuge Machine?

Centrifugation is the process of using centrifugal force to accelerate natural separation. Instead of waiting for gravity to settle particles over hours, the centrifuge applies forces hundreds or thousands of times greater — compressing that wait into minutes.

Separation happens through sedimentation: denser particles sink outward to the tube bottom while lighter components remain suspended. Four variables control how quickly and completely that happens:

• Benchtop centrifuge – Compact centrifuges for routine laboratory work
• Microcentrifuge – Small-volume sample processing
• Floor-standing centrifuge – Large capacity for high-volume labs
• Large capacity centrifuge – Handles multiple samples simultaneously
• STAT centrifuge – Rapid processing for urgent clinical tests
• Refrigerated centrifuge – Temperature-controlled sample separation
• High-speed centrifuge – Increased RPM for faster separation
• Ultracentrifuge – Extreme speeds for specialized applications

Choosing the right type of centrifuge depends on your laboratory’s sample volume, processing speed requirements, and specific applications.

What is Centrifugation?

Centrifugation is the process of concentrating the natural forces that act on all particles of different densities to accelerate the natural process of separation. It is what separates the particles by density in the test tube. Centrifugation can occur with either filtration or sedimentation methods. Filtration uses a mesh screen to hold back the solid components and allow the liquid components to flow through. Filtering does not work to centrifuge blood samples because the blood components are too small.

In either method, the particles are suspended in liquid and separated in the centrifuge machine. The separation happens due to centrifugal force, which pushes objects outward – toward the tip of the tube, in the case of blood tubes – as they are spun around in a circle.

Principles of Centrifugation

At its core, centrifugation is separation through sedimentation. The denser particles sink to the bottom of the container, while the more lightweight particles remain suspended. Centrifugation will displace particles that are even slightly different in density, and is influenced by these four factors:

• The density of the samples and solution
• The temperature and viscosity
• The distance that the particles are displaced
• The speed of rotation

Relative centrifugal force (RCF), or G-force, is the amount of acceleration that is applied to the sample. When RCF exceeds the buoyant and frictional forces in the sample, the particles will move away from the axis of rotation and result in sedimentation.

What Is a Centrifuge Used For? Common Laboratory Applications

Because centrifuge machines are excellent at separating particles by density, they are often found in laboratory settings where it is necessary to isolate certain biological components for testing. Common centrifuge applications include:

In a blood sample, for instance, there are red blood cells and plasma mixed together. After centrifugation, the red blood cells will be at the bottom of the tube and the plasma will be on top.

Laboratory centrifuges are necessary for research on particular components, such as separating out blood plasma for testing, isolating DNA, purifying proteins, analyzing urine sediment, and preparing samples for diagnostic testing.

How Does a Centrifuge Work?

The purpose of the centrifuge machine is to replicate and accelerate centrifuging to separate components in a sample. Because of the forces involved, these machines are carefully designed to work efficiently while keeping the operator safe.

Centrifugal force is the key principle behind how centrifuges work. When samples spin at high speeds, centrifugal force pushes denser materials outward while lighter materials remain closer to the center. This rapid separation process—called centrifugation—delivers results in minutes instead of hours.

What centrifuge speed is right for my sample?

Protocols specify RCF rather than RPM because the same RPM produces different forces on rotors of different radii. The ranges below are general clinical reference — always follow your analyzer or reagent manufacturer’s protocol.

For the RCF-to-RPM conversion formula and a worked example, see our guide on how to calculate RCF.

Parts of a Centrifuge: Key Components Explained

At the center of the centrifuge is a powerful motor that creates the spin. Attached to this motor is the rotor, in which will rest the containers that hold the tubes containing the material to be centrifuged. These containers may be spun at a 45-degree angle (fixed angle centrifuge), a 90-degree angle (horizontal centrifuge) or no angle (vertical centrifuge). Depending on the centrifuge, the tubes may either be loaded at the angle on which they will rotate (fixed angle is a good example of this) or be loaded into a container that will adjust itself to a different angle upon startup. This second methodology is referred to as swing bucket and is a common functionality in horizontal centrifuges.

Depending on the centrifuge selected, a variety of different controls may be available. Some centrifuges are pre-programmed for one, two, or three processing settings. Some are completely custom programmable with a digital display. Regardless of the control type, when you start the centrifuge, it will run the motor based on the settings provided. During the cycle, the sample in the test tubes will separate into their various components so they are ready for analysis.

How to Use a Centrifuge: Step-by-Step Operating Instructions

Despite the complex principles at work in the centrifuge, operating the machine itself is quite simple. To use a centrifuge machine:

1. Insert the test tube sample into one of the portals
2. If needed based on the number of samples you are testing, insert test tubes filled with water for balance
3. Secure the lid and select desired settings
4. Start the centrifuge and wait for it to complete the cycle
5. When the centrifuge has stopped spinning, take out the balances and samples
6. Each sample will now be separated into its various components and ready for analysis

Knowing how a centrifuge machine works is key to using it properly.

How to Balance a Centrifuge Machine Properly

When using a centrifuge machine, it is necessary to balance your samples. Balance the centrifuge machine by:

• Making sure all tubes are evenly filled with liquids similar in density
• Ensuring that the masses of the tubes are within 0.1 grams of each other
• Placing tubes opposite from one another inside the machine to keep the gravity in the center

When you test an odd number of tubes, it may not be possible to create balance. In these cases, fill another test tube with water and balance based on density and mass.

Centrifuge Maintenance: Care Tips for Laboratory Equipment

Ensure your centrifuge receives the proper care and maintenance so it provides reliable results, is safe to use and works for a long time. Regularly perform these checks:

• Education: Make sure that everyone who uses the centrifuge machine knows how to use it. Teach all laboratory staff how to balance samples, set speeds and take safety measures.
• Inspection: An inspection will alert you to any problems with the centrifuge machine. Look at the components for scratches or effects of chemical exposure. All are signs of wear and should be fixed as soon as possible.
• Awareness: When using the centrifuge, be aware of signs that something is wrong. If the machine is shaking, vibrating or grinding, stop it immediately.

Cleaning and disinfection are key to ensuring good centrifuge functionality in the long term. Using a neutral cleaning solution (like an alcohol-based disinfectant) and a soft cloth, wipe the:

• Rotors
• Rotor chamber
• Accessories
• Interior area
• Keypads
• Touch screens

Frequently Asked Questions

How fast does a centrifuge spin?

Speed depends on the centrifuge type and application. Clinical and benchtop centrifuges run at 300 to 5,000 RPM, producing forces of roughly 600 to 7,000 ×g. STAT centrifuges for urgent processing can reach 8,500 RPM. High-speed and ultracentrifuges used in research exceed 15,000 RPM and can generate more than 100,000 ×g. The right speed for any protocol is specified as RCF, not RPM, because RCF accounts for rotor radius.

What do centrifuges do to blood samples?

The buffy coat layer is typically less than 1% of the total blood volume but contains all the white blood cells and platelets — making it the critical layer for complete blood count interpretation and certain diagnostic applications.

What’s the difference between RCF and RPM?

RPM measures how fast the rotor spins. RCF (relative centrifugal force, also called G-force) measures the actual force the sample experiences. They’re related but not interchangeable — the same RPM produces different RCF on rotors of different radii. This is why lab protocols specify RCF: it’s the only way to get consistent results across different centrifuges. For the formula and a conversion table, see our guide on how to calculate RCF.

Why does my protocol specify RCF instead of RPM?

Because RPM alone doesn’t tell you the force your sample experiences. A rotor spinning at 3,000 RPM in a small microcentrifuge generates far less centrifugal force than a large rotor at the same speed. RCF (relative centrifugal force) accounts for both speed and rotor radius, so protocols written in RCF produce the same separation regardless of which centrifuge you use.

The relationship: RCF = 1.12 × r × (RPM/1000)², where r is the rotor radius in millimeters. Most centrifuge manufacturers publish the rotor radius in the instrument manual. If you’re working from a legacy protocol written in RPM, convert it to RCF before adapting to a new instrument.

Shop Drucker Diagnostics Centrifuge Machines Today

Does your laboratory need reliable, high-quality testing equipment? As the industry’s leading supplier and manufacturer of centrifuge machines and more, Drucker Diagnostics is here to keep your lab running. Shop our products and accessories today, and feel free to contact us with any questions.