High Speed Centrigfuges

Author: Michael Brush
Date: September 29, 1997

Imagine working in a life science lab without a centrifuge. Be it a microfuge, a general purpose centrifuge, or even an ultracentrifuge, little work would be accomplished in its absence. Unquestionably, these ubiquitous and indispensable instruments have made an incalculable contribution to our scientific understanding of the world. Where would we be without them?

Fortunately, the centrifuge has come a long way since the old hand-cranked contraptions that clamped onto a bench top. State-of-the-art technology has produced several powerful, versatile, and elegant machines. Just like cars, these centrifuges range from basic models, with little more than a speed control knob, rpm gauge, and a timer, to fully loaded models offering video programming, w2dt integration capabilities, electronic rotor identification systems, temperature compensation software, and fast, high-torque drives. High speed, high capacity, low capacity, general purpose, table top, and high performance are just a few of the types of centrifuges offered by manufacturers, but the distinctions and combinations soon blur together. Indeed, the classification of these machines has become very difficult. As Ken Johnson, Product Manager for Beckman Instruments, explains it, "Centrifuge manufacturers are now driven more by applications than just size or speed requirements when designing new instruments. What used to be a floor standing centrifuge is now a bench top model, and bench top models can become floor models very easily."

To bring some order into this muddle, LabConsumer picked a class of centrifuges, dubbed it "high speed," and defined it to include any centrifuge that spins between 17,000 and 30,000 rpm and runs interchangeable rotors with capacities of up to 6 liters. Any machine that operated above that rpm range was considered an ultracentrifuge, and anything below was considered low speed. This resulted in a profile of 31 separate machines produced by eight manufacturers.

Split almost equally between table top and floor standing centrifuges, the prices of this group ranged from $1,253 to over $38,000, with most of the table top models priced under $8,200. Rotors are extra and add a considerable amount to the final price.

The table top models usually had smaller maximum rotor capacities, especially for their fixed angle rotors, reflecting the most commonly used tube size of 15 ml. With their small footprints, reduced space requirements, and lower prices, table top models are becoming personal centrifuges because they fit easily on a researcher's bench, unlike their larger floor model cousins that are often relegated to a common machine room down the hall. Aided by advances in microprocessor and rotor technology, some of the table tops, like Jouan's MR 22i and Sorvall's Super T-21, come close to matching the floor models in versatility and performance. The floor model machines, on the other hand, offer higher g-forces and rotors with larger sample volumes, such as Beckman's 6-liter J-Lite" JLA-8.1000. The floor models also run a wider range of rotors. Sorvall, for example, offers a selection of 29 different rotors for its RC-series centrifuges, and Beckman provides a selection of 31 rotors for its Avanti J and J-series centrifuges.

Most of the machines feature selectable acceleration and deceleration profiles, and 19 have memories for 10 to 50 user-defined programs. The higher-end machines feature w2dt integration capabilities for ensuring run-to-run reproducibility, automatic rotor identification systems that exploit some interesting technologies, and self-diagnostic functions. Some machines, like Jouan's KR 22i, include a rotor radius correction system that adjusts RCF values when rotor adapters are used, providing more accurate g-forces than machines using coded rotor identification systems. Several table top models are offered in both ambient and refrigerated versions, and all the floor models are refrigerated. While the refrigeration systems are billed as CFC-free, this term is rapidly losing its impact as a selling point because CFC-free systems are widespread throughout the profile.

One-year warranties are commonplace, with some manufacturers offering additional two- to five-year warranties on drives and refrigeration systems.

Let's Go for a Drive

A centrifuge is nothing without its drive. Most centrifuges today belong to the direct drive class, in which the motor armature, or drive shaft, drives the rotor directly without any intervening pulleys, gears, or belts. Historically, copper or carbon conductors, called brushes, carry the current from the stationary part of the motor to the moving shaft or armature. Friction and electrical arcing, caused by the current reversals necessary for braking, wear down the brushes, which then need periodic maintenance and replacement. Brush-type drives also require more time to ramp up to their set speeds, extending acceleration and deceleration times in comparison to the newer-technology drives.

Currently, the majority of high speed centrifuges use brushless motors. Most of these are known as induction drives, consisting of a nonwound permanent magnetic shaft surrounded by a series of stationary coils. The passage of a variable electric current through the coils induces the shaft into motion. Acceleration rates are modified by adjusting the frequency of the current changes.

The latest type of drive found on high speed centrifuges is the switched reluctance drive. Essentially a beefed-up induction drive, the coils in the switched reluctance drive are wound differently to give maximum torque, or turning force, over the entire acceleration spectrum. This translates into plenty of power to get a heavy rotor up to maximum speed in a hurry, greatly reducing run times. Having seen use early on in mopeds, the technology for switched reluctance drives has been around for some time. It's taken the recent application of computer technology to provide the previously unavailable acceleration and deceleration control necessary to make switched reluctance drives suitable for centrifugation.

Without any brushes to worry about, inductance and switched reluctance drives require very little maintenance other than an occasional bearing replacement. They also run with less noise than brush-type drives. Braking is accomplished by slowly reducing the frequency of the current changes to the drive motor.

The Spin Doctors

Here's the spin on 31 high speed centrifuges.

Avanti J-201
from Beckman Instruments

Beckman Instruments, Inc.: Avanti-20, Avanti J-20I, Avanti J-25, Avanti J-25I,; Avanti J-30I, J2-HC, J2-HS, J2-MC

With several centrifugation breakthroughs, like the first commercially available ultracentrifuge and the first microfuge, Beckman has been involved with centrifugation since 1954. Now, with the incorporation of the new SR drive* (switched reluctance) into its high speed centrifuges, Beckman has launched a new category of high speed instruments, the Avanti¶ J Series High Performance Centrifuges. Beckman believes the advances in the Avanti design are so significant it created this new centrifuge category of high-performance machines.

Ergonomically designed with lower profiles to ease rotor exchange and to save space, the Avanti series' high torque SR drive accelerates and brakes in half the time of conventional drives, delivering higher speeds and g-forces with larger volume rotors and producing considerable time savings across multiple runs. These drives also tolerate sample imbalances up to 5 percent of the sample volume, which permits tube balancing by the naked eye.

All models of the Avanti J series feature Beckman's Friction Reduction System (FRS¶). Here, a maintenance-free vacuum pump creates a reduced atmosphere inside the chamber, reducing friction on the spinning rotor and easing the work load on the drive and CFC-free refrigeration system, enhancing centrifuge performance. The digital "I" version models also feature advanced programmability and Beckman's Instant Rotor Identification System (IRIS¶) which turns each rotor into a miniature radio station broadcasting its specific identification code. Once the centrifuge receives this signal, it automatically engages critical speed and timing parameters.

Five instruments comprise the Avanti J series. The Avanti J-25 and J-25I generate 75,600 xg at 25,000 rpm and have a maximum capacity of 3000 ml. Single tube sizes range from 1.5 to 500 ml. The Avanti J-30I is almost in ultracentrifuge territory, generating over 100,000 xg in both fixed angle and swinging bucket rotors at speeds up to 30,000 rpm. Maximum and single tube volumes are equal to those for the Avanti J-25.

The newest members of the Avanti J family, the J-20 and J-20I, are large-capacity models. Sold as separate systems, these two machines include Beckman's new carbon fiber and aluminum composite rotor, the J-Lite" JLA-8.1000, as part of the package. This rotor generates g-forces up to 15,900 xg at 8000 rpm and holds six 1-liter bottles. Swinging bucket rotors are also available for volumes up to 4 liters and forces up to 4000 xg. With other Beckman rotors in place, the J-20 series reaches over 51,500 xg.

For greater throughput, added safety, and operator convenience, Beckman has applied advanced technology to its high-speed J2 Series centrifuges. With a long performance record, these durable machines feature the Friction Reduction System and CFC-refrigeration. The J2-MC and J2-HS generate speeds of 21,000 rpm and forces up to 51,500 xg. The digital, microprocessor-controlled J2-MC has programming options not found on the analog J2-HS. Beckman's J2-HC centrifuge combines high speed and high capacity with conventional high speed rotors at speeds up to 18,000 rpm, producing 47,900 xg. The J2-HC runs Beckman's largest swinging bucket rotor, the JS-4.3, which has a maximum capacity of 3 liters at 4,220 xg.

Avanti J and J2 Series centrifuges are manufactured in an ISO 9001 facility and meet the world's highest standards for quality and operator safety, certified by the CE marking and UL and CSA approvals. Beckman offers a complete range of aluminum, titanium, and carbon fiber rotors for these instruments, including continuous-flow versions and its unique Elutriator rotors.

*SR drives are manufactured by Beckman Instruments with technology licensed from Switched Reluctance Drives, Ltd., Leeds, United Kingdom.

B. Braun Biotech Sigma 3K30

B. Braun Biotech, Inc. USA: Sigma 3K30

B. Braun Biotech's Sigma 3K30 refrigerated high speed centrifuge is a table top model with a maximum capacity of 6 x 85 ml tubes. A brushless drive revs up to 30,000 rpm in 45 seconds, generating a maximum g-force of 64,396. Freely programmable, the microprocessor-controlled Sigma 3K30 provides a total of 20 acceleration and deceleration curves and 100 storable programs. Its CFC-free refrigeration system maintains a temperature range of -20ºC to +40ºC.

Safety features in the Sigma 3K30 include a motorized lid lock and an aerosol containment system. Twelve fixed angle rotors for tubes between 1.5 to 85 ml are available, along with one horizontal rotor for 10 ml tubes and a drum rotor that will hold 60 to 120 microtubes. The rotors are protected by a magnetic rotor identification system that prevents overspeed problems.

Heraeus Instruments, Inc.: Biofuge 22R, Contifuge 17RS,; Contifuge 28RS, Suprafuge 22

Global centrifuge manufacturer Heraeus Instruments offers four high speed centrifuges in table top and floor standing configurations.

The bench top Biofuge 22R provides researchers with speeds to 22,000 rpm and g-forces to 31,925. Microprocessor-based electronics are designed to assure accurate and reproducible results. The individually selectable temperature, speed, and run time parameters are indicated on easy-to-read LED digital displays. Incorporating a quiet induction drive, the Biofuge 22R accommodates 11 fixed angle and swing out rotors with sample tubes ranging from 1.5 to 100 ml.

Designed for everyday use in the lab, the refrigerated Contifuge 17RS and it big sister, the Contifuge 28RS, form a family of table top centrifuges. The 17RS spins up to 17,000 rpm with 25,850 g's, while the 28RS whirls along at 28,000 rpm with g-forces reaching 51,710. Both feature a brushless induction drive system and microprocessor-based electronics with LED displays for each operating parameter. Programmable, they enable the selection and storage of up to 32 user-defined programs and nine acceleration/deceleration profiles. A touch-sensitive keypad simplifies data entry, even for gloved users. Both machines accommodate the same range of rotors as the Biofuge 22, in addition to a unique continuous flow rotor with a 600-gram sediment capacity.

Heraeus manufactures the floor standing Suprafuge 22 for scientists working with larger sample volumes or needing greater throughput or RCF. Providing 60,600 g's at speeds up to 22,000 rpm, the ergonomically designed Suprafuge 22 simplifies large-rotor changes with its conveniently positioned waist-level rotor chamber. Microprocessor control enables up to 33 user-defined operation profiles to be easily stored and recalled. In addition to its maintenance-free brushless drive, the Suprafuge 22 features digital displays, a touch-sensitive keypad, automatic rotor identification, self-diagnostics, and a lockable control panel. It runs 10 fixed angle and swing out rotors with tube volumes ranging from 1.5 to 500 ml.

All Heraeus centrifuges are manufactured in an ISO 9001 environment and conform to internationally recognized centrifuge safety standards.

Z382 and Z382K from Hermie

Hermle: Z 323, Z 323 K, Z 382, Z 382 K

Distributed by National Labnet, Hermle offers four of the lowest-priced table top centrifuges examined in this profile. All four operate at a maximum 17,000 rpm, generating 26,800 xg. These machines consist of two series of instruments provided in either refrigerated or ambient configurations. The smaller Z 323 and its refrigerated big brother, the Z 323 K, handle a maximal 4 x 100 ml tubes in a swing out rotor, or 6 x 85 ml tubes in a fixed angle rotor. The larger, ambient Z 382 and the refrigerated Z 382 K spin 4 x 250 ml bottles. A broad range of rotors, spinning everything from microtiter plates to hematocrit tubes, microfuge tubes, and 100 ml and larger tubes, is available.

All four feature quiet induction drives, a hybrid control panel consisting of a microprocessor with easy-to-adjust knobs, and the selection of rpm or RCF value spin modes. Speed values are adjustable in 10 rpm increments. Both series also feature program memory for storage of up to 10 programs and a rotor recognition system that sets individual rotor parameters based on a coded magnetic indicator ring in each rotor. Finally, the refrigerated models maintain temperatures from -10ºC to +40ºC.

Hettich EBA 12

Hettich Zentrifugen: EBA 12, EBA 12R,; Universal 16, Universal 16R

Connecticut-based RevPro, Inc, serves as the North American distributor for German centrifuge manufacturer Hettich Zentrifugen. Hettich builds nearly two dozen centrifuges, of which four qualify as high speed, running up to 18,000 rpm and dishing out 23,907 g's. All four are bench top machines and feature microprocessor control that allows the easy entry of speed, RCF, radius, running time, acceleration and braking rates, and cooling and pre-cooling programs for the refrigerated models. Each has a maintenance-free drive and an electronic rotor identification system.

The smaller EBA12 series, consisting of the ambient EBA12 and the refrigerated EBA12R, are the two lowest-priced centrifuges in this profile. Both run seven rotors, with a maximum capacity of 6 x 50 ml tubes in the fixed angle rotor and 6 x 15 ml tubes in the swing out rotor. Hettich highly recommends these machines for microliter centrifugation. The larger Univeral models, the ambient Universal 16 and the refrigerated Universal 16R, have a bigger chamber that accommodates six more rotors than the EBA models. Both run a larger capacity swing out rotor that holds 4 x 100 ml bottles.

Hettich Zentrifugen is an ISO 9001-certified company.

IEC: B-22M

IEC, or the International Equipment Company, introduced the first large capacity 20,000 rpm centrifuge system almost 50 years ago. Those years of experience have led to the latest-generation IEC centrifuge, the B-22M. A floor model centrifuge, the B-22M features a space-saving front-to-rear air flow pattern, permitting its installation between benches or side-by-side placement of instruments.

Driven by a proprietary belt drive with an automatic imbalance shut-off feature, the B-22M develops a maximum 49,300 xg spinning up to 22,000 rpm. Insulating foam and two heavy-gauge steel bands surround the stainless steel chamber, providing absolute mechanical containment in the event of a rotor accident.

The B-22M's high-efficiency CFC-free refrigeration system maintains temperature to within 1ºC without the need for a chamber vacuum. Sample temperature control is aided by IEC's patented Turbo Cover chamber lid, which also improves rotor stability at high speeds. Other features include a glove-friendly membrane control panel with logically arranged international symbols and a 10-program memory with a key lock, making the B-22M suitable for production and multi-user situations. G-force values may be entered directly for ease of reproducing published procedures, and an w2dt integrator system is also standard.

A variety of specially designed and machined rotors is available for the B-22M. Several boast low k-factor designs that result in fast separations. IEC manufactures the B-22M in an ISO 9001-certified environment following IEC 1010-2-2 standards and has CSA certification.

The GR20.22 from Jouan

Jouan, Inc.: MR18.12, MR22i, KR22i, GR20.22

With 70 years of experience as a centrifuge manufacturer, Jouan, Inc. brings plenty of low and high speed centrifuges to the marketplace and boasts of being the first centrifuge manufacturer to use CFC-free fluids and insulation in its products. Jouan manufactures four high speed centrifuges, comprised of two floor models and two table tops. While these share common features, each has it own special attributes.

The first floor model, a high-capacity high speed centrifuge called the KR22i, generates up to 63,400 xg with a high torque, brushless induction drive. Jouan's Thin Film Technology (TFT) refrigeration system creates a powerfully cooled chamber wall that is designed to maintain actual protocol temperatures in the sample and not just the rotor. The KR22i's programming accepts the entry of the rotor's radius so that the true RCF value applied during a run is displayed. This feature also applies when adapters are inserted into the rotor, providing RCF values that are much more accurate when compared to systems using coded rotor-control systems. An integration feature ensures absolute run-to-run reproducibility.

Jouan supplies six alloy and four carbon fiber rotors for the KR22i that cover the majority of high speed centrifuge applications. The KR22i also accepts a wide variety of other manufacturers' rotors.

For researchers needing a medium capacity, high speed refrigerated centrifuge with a compact 55 x 66 cm footprint, Jouan offers the GR20.22. At 90 cm high, this centrifuge's working height makes sample entry and rotor exchange comfortable and easy.

The GR20.22 features programmable temperature compensation and radius-controlled RCF calculation like the KR22i. An ergonomically positioned control panel facilitates the use of 50 storable programs that function in both RCF and RPM modes with integrator control. Several safety features, including a dual lid interlock, an armor plated chamber, and imbalance detector are standard items.

A range of eight rotors, one with a maximum capacity of 6 x 290 ml bottles, supports the gamut of centrifuge applications.

Billed as a multi-function centrifuge because of its ability to accept and run both low- and high-speed rotors with equal ease, the bench top MR22i shares several features with the KR22i. These include a quiet induction drive, TFT refrigeration, temperature compensation software, and control by integration.

The MR22i boasts a unique interactive screen control system called VIDEOset that employs drawings, diagrams, and dynamic graphics to communicate with the user. Jouan's patented AUTO-LOCK system endows the MR22i with its multi-functional capabilities of low- and high-speed runs with swing out, angle, drum, and microtiter plate rotors. AUTO-LOCK allows each of the 10 available rotors to simply "click" onto the drive shaft without the use of tools or the need to screw the rotor down. Removal is direct and immediate.

Jouan's refrigerated MR18.12 is a classic, low-priced table top centrifuge. Operated by basic analog control, the MR18.12 generates 20,100 xg at speeds up to 21,000 rpm, and accommodates a maximal 4 x 100 ml tubes. A "pulse" button feature makes very short runs possible with small rotors.

Sorvall RC-26 PLUS

Sorvall Products, L.P.: RC-5B PLUS, RC-5C PLUS, RC-26 PLUS, RC-28S, Super T-21

Operating once again as an independent company, Sorvall Products, L.P., is no longer a part of DuPont. Since the introduction of the RC-1-the first refrigerated high speed centrifuge-in 1951, Sorvall's high speed machines have evolved into a family of laboratory workhorses. Currently sold as the RC-5B PLUS and the RC-5C PLUS, these "Superspeed" machines run up to 21,000 rpm and produce over 51,000 g's. The economical, easy-to-operate RC-5B PLUS features analog displays and lamp indicators. Rotor speeds are maintained to within 1%, and temperatures are held to within 1ºC of set conditions between 2ºC and 37ºC. The fully featured, microprocessor-controlled RC-5C PLUS comes loaded with plenty of options. These include levers and digital LED displays for setting and reading run parameters, an w2dt integrator, and automatic RCF calculation. Both machines employ conventional brush-type direct drive motors.

Sorvall's RC-26 PLUS expands the range of its Superspeed machines to 26,000 rpm and 70,450 g's. Propelled by a 3-horsepower induction drive, which, when combined with its Superlite Rotors, offers some of the fastest acceleration and deceleration times in the industry, the RC-26 PLUS features a push-button, digital control panel, fast instrument setup capability, precise temperature control, 20 user programs, run control options, and w2dt integration.

Stepping up to the low end of ultracentrifugation, the RC-28S refrigerated SUPRAspeed^TM centrifuge rockets up to 28,000 rpm and dishes out a potent 100,500 xg. The induction drive of the RC-28S incorporates a Gyro-Action Self-Centering system that permits eye balancing of tubes, provides an automatic imbalance detector, and contains the new Sorvall Positive Action Brake System, which maintains positive controlled braking down to 0 rpm. Combined heating and cooling capabilities have been designed to maintain precise temperature control, especially at higher temperatures. Finally, Sorvall's SPIN-RIGHT^TM Rotor Management System on the RC-28S exploits ultrasonic rotor-imaging technology to automatically identify rotors and ensure safe, optimal instrument control.

The Sorvall SUPER T 21 Benchtop Superspeed is billed as the personal, three-centrifuges-in-one machine. With 21,000 rpm and 49,555 xg capabilities, the SUPER T 21 is a bench top superspeed with floor model speed capability, a refrigerated microfuge, and a large capacity (3 liters) low speed machine. Its compact size and quiet operation mean the SUPER T 21 will fit on the bench top in the lab and not in a machine room down the hall. This machine features microprocessor control, QUIKset^TM menus, 10 storable programs, and SOFTspin¶ rotor control.

Two companies that manufacture rotors for many high-speed centrifuges are Composite Rotor Inc. (CRI) and Piramoon Technologies Inc. (PTI). CRI, founded in 1990, uses state-of-the-art carbon fiber composite materials to replace more common aluminum and titanium used in other rotors. CRI rotors are manufactured to provide greater strength, lower fatigue, and lighter weight than conventional rotors. For more information, contact CRI at 800-745-8669 or www.composite.com
PTI also manufactures several high-speed rotors from composite materials. The new FA-10c FiberLiteCentrifuge rotor is billed as being half the weight of similar metallic rotors, reducing the risk of worker injuries and minimizing wear-and-tear on the centrifuge drive. For more information, contact PTI at 800-PTI-FUGE or www.piramoon.com.
Sorvall manufactures nearly 30 rotors for its high speed centrifuges. These include the Superspeed rotors, SUPRAspeed rotors, and the specially designed SUPER-LITE¶ aluminum rotors that are up to 50% lighter than conventional rotors. Several have been independently tested for biocontainment capabilities.

Final Pellets

Centrifuge field service engineers represent a good source of information concerning specific centrifuge models. "Of course," says Bernard Schwartz, a Senior Service Specialist for Sorvall, "field service engineers can be a great resource in the buying decision and can often direct a consumer to the most reliable instruments. Not only does this make the customers happier, but the service engineers' jobs are easier as well." He goes on to say that sales people and service engineers should work closely together to best meet their customers' needs. Other good sources of information include hospital biomedical departments and independent instrument service companies that do contract work for centrifuge manufacturers without their own service departments. Altogether, they are useful people to talk to the next time you need a high speed centrifuge.

Table Comparing Products

Michael Brush is an Associate Scientist and Radiation Safety Officer at Hitachi Chemical Company in Irvine, CA. He can be reached online at MDBrush@compuserve.com.

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