Caitlin Smith has a B.A. in biology from Reed College, a Ph.D. in neuroscience from Yale University, and completed postdoctoral work at the Vollum Institute.
You know you should probably clean your centrifuges regularly, but do you know exactly how to do it, and when? Do you know how to perform other maintenance tasks, and can you recognize the warning signs that indicate a repair is needed?
These are important skills for any lab that uses a centrifuge, yet beyond wiping up the occasional minor spill, many lab workers are unsure of how to keep their centrifuges in tip-top shape. Here's what you need to know.
Keeping clean
Cleaning the outside of a centrifuge usually entails wiping with a soft cloth either alone or with a mild cleaner. This could be water, mild soap or a commercial product. “I have found that [Formula] 409 works well on surfaces for general cleaning,” says Tom Di Francesco, a service engineer at BioNiQuest Lab Services. “Care should be taken around some decals, laminated surfaces and other printed instructions on the panels.”
There is no best cleaner for the inside of a centrifuge—they can have plastic, ceramic, aluminum or stainless steel surfaces. The best advice: read the (“bleeping”) manual. “You should always follow the manufacturer’s recommendations on how to clean and what with,” says Lane Smith, president and senior engineer at Phoenix Technical Services (no relation to the author). “For instance, some cleaners, like bleach, can attack the stainless steel of the bowl and discolor it or damage it.” Don’t flood the inside of the centrifuge. If you cannot locate your centrifuge’s manual, download a PDF—and keep a hard copy near the instrument for reference.
Maurizio Merli, product director for centrifugation at Thermo Fisher Scientific, recommends any domestic cleaner of pH 6 to pH 8 for general cleaning of the lid, case and control panel. For disinfecting—when using the centrifuge for biological samples, for example—Merli says rotors and accessories can be sprayed with disinfectant or autoclaved at 121°C for 20 minutes. “Metal rotors will need a thin layer of anticorrosion oil before going back to service, whereas carbon fiber rotors, such as our Thermo Scientific Fiberlite™ rotors, are immune [to] corrosion and generally require less TLC,” he says. Popular disinfectants include 70% ethanol or 10% bleach, Di Francesco says, "depending on [the lab's] protocols.”
To remove radioactivity, Merli suggests a decontamination solution of 70% ethanol and 10% sodium dodecyl sulfate in water. “Parts will need to be rinsed with ethanol first, and finally with de-ionized water,” following decontamination, he says. Thomas Neumann, vice president of marketing and sales for Europe at Sartorius Lab Instruments, recommends a “standard decontaminating cleaning solution, [such as a] typical bench-surface cleaning solution for molecular-bio labs.”
Avoid microparticle-based cleaners such as stainless-steal cleaning solutions, Neumann says. Likewise, Smith recommends avoiding “harsh cleaners, steel wool or scrubby pads.” Avoid also “chemically aggressive” solutions on metal parts such as hinges, hooks, motors, rotors and the centrifuge bowl, says Merli. “Soap suds, phosphoric acid, bleach solutions [and] scrubbing powder are caustic agents. Even stainless steel may show signs of corrosion over time if exposed to them,” he says. “Solutions with mercury, copper and other heavy metal ions … should also be avoided.”
Most centrifuge manuals include a “Chemical Compatibility Table” or “Chemical Resistance Chart” indicating which chemicals or cleaners are compatible, and which are not, with your centrifuge’s surfaces.
Some centrifuges, such as pharmaceutical-duty filtering centrifuges, are equipped with a clean-in-place (CIP) system that cleans parts of the centrifuge automatically. “This design [is] characterized by mechanically polished and electro-polished surfaces, welds ground smooth and flush, minimal areas for product hang-up, no threaded connections in the process zone and pitched slopes to ensure that the CIP fluid and debris can adequately drain with high repeatability,” explains Greg Cybulski, senior business development director for textiles and environment at Rousselet-Robatel.
Moisture
In some centrifuges, it is easy to see accumulated moisture or condensation and wipe it out. In others, the centrifuge’s bottom is obstructed by the rotors, so moisture can build up unnoticed. Accumulated condensation can freeze, leading to "uneven and restricted air flow around the rotor, which will cause a variety of problems, including stress on the drive system,” Di Francesco says. If you cannot remove the condensation yourself, call a professional service engineer.
Rubber seals
Some centrifuges (ultras and other high-speed models) have vacuum systems that require rubber seals on the chamber. It is important to keep these seals clean and in some cases lubricated. Ultracentrifuges, in particular, need a functioning seal to create a strong enough vacuum to run. Note, too, that vacuum systems can complicate spills. “When you have a spill in a centrifuge with a vacuum system, a portion of that sample will get sucked into the pump or drive motors,” says Di Francesco. “Bearings and motor windings do not like moisture.”
Fans and condensers
Many centrifuges have fans and refrigeration condensers. Although some are accessible to users, most are not, says Di Francesco. Often these parts are protected by air filters, because condensers “need to be kept clean of dirt and dust,” he says. “When a condenser gets clogged, the air flow is restricted, and the compressor overheats.” Service engineers can maintain these at maintenance visits. If the air intake for the condenser doesn’t have a filter, “invest in a small vacuum [cleaner] to keep it dust free,” suggests Smith.
Cleaning schedule
Neumann says centrifuges should be cleaned routinely about once a week, and also any time sample spills.
When cleaning spills, be sure to clean the entire centrifuge, not just obvious puddles. “Biological samples spilled in the bowl of a ventilated centrifuge can be spread in the air during the run, whereas chemical samples or reagents may corrode various centrifuge parts—the bowl, rubber gaskets and even the temperature probe in refrigerated centrifuges,” says Merli.
Warning signs indicating that immediate cleaning may be needed include the presence of residue or moisture, or unusual sounds during operation. “If you start a conventional centrifuge, and it sounds like gravel in a washing machine, you need to stop it and clean whatever broken tubes or loose sample caps are floating around,” says Smith.
To track centrifuge maintenance, keep a logbook and maintenance routine for each machine. Logbooks are especially valuable for centrifuges used by multiple labs, such as in core facilities, says Di Francesco. In this case, “someone needs to be in charge and monitor the centrifuge,” because these “are the hardest to supervise and generally suffer the most.”
Skimping on cleaning can have expensive repercussions. “Spindle and motor repairs are getting more expensive as manufacturers continue to raise their prices in an effort to sell you the latest and greatest,” says Di Francesco. Manufacturers also expect centrifuge users to clean the rotor and centrifuge interior and to follow all instructions for use. “Damage to the machine due to improper balancing and tube failure is not covered by service contracts or warranties,” says Di Francesco -- and of course, poses a potential safety hazard.
Mistakes to avoid
Mistakes are human nature, but a little forethought can prevent some mishaps. For example, centrifuges can have temperature or optical sensors inside the bowl, which are delicate and should be handled with care. Keep the sensor wires clean, but don’t pull on them accidentally when cleaning, Di Francesco advises. One centrifuge, the Beckman Ultra, has a window on the safety plate that covers the radiometer. “It is not a glass or plastic cover that can be cleaned—it is more like a thick cellophane,” he says. “If you poke your finger into it, then it will collapse.”
Another mistake is forgetting to balance the centrifuge. Some rotor tubes have rubber stoppers under them. “Make sure that all of the tubes get the stoppers back in,” says Smith. “A severely unbalanced centrifuge tends to make life a little too exciting.”
Di Francesco says high-speed rotors will last a long time if kept clean—but if not, they will deteriorate more quickly than you might expect. A painted surface usually protects high-speed rotors from corrosion, but spill residues on the rotor “will eat through the paint, and once the paint is breached, the process of stress corrosion begins,” he says. In particular, he says, “The section of the rotor which mates onto the spindle is often neglected.” This core should be cleaned regularly, because if corrosion causes the rotor to stick, getting it off can damage the spindle.
Merli also recommends that researchers clean and grease the rotor trunnions at least weekly, if the centrifuge is used every day. “A large portion of poor sample separations are due to vibrations originating from rotor buckets not swinging smoothly during the braking phase,” he says.
When to call for help
No matter how much preventative maintenance you do, there are times when you should call in a professional service engineer. Here are some warning signs to look out for.
Unusual sounds
Di Francesco emphasizes the importance of being a good listener. “If you hear knocking noises or scraping or grinding noises that you have not noticed before, or if the compressor is laboring or excessive heat is being expelled from the exhaust section, these may all be signs of trouble,” he says. But even the most alarming sounds aren’t necessarily a death sentence. “Most problems can be remedied with a repair or adjustment,” he says. “The cost of a repair will outweigh the cost of a new centrifuge.”
Unusual substances
Other warning signs involve “contamination that cannot be removed or oily substances on the ground of the centrifuge,” says Neumann. Smith notes that the motors of older centrifuges had carbon brushes. “If you clean up a pile of black dust from under the centrifuge, then you may want to check when the last brush change was performed,” he says. Even though some models allow you to change brushes yourself, it’s usually better to have a service engineer look at it. “They will be able to disassemble the motor to the point of blowing or vacuuming out the carbon dust as well as [determine whether] the speed and temperature are within specification,” says Smith.
Corrosion
Corrosion is obviously bad, but it may be worse than you think. Those brown or gray spots can be indicators of deeper structural problems that require professional attention. “Corrosion cracks the inner structure of a metal or plastic part and compromises severely its life and integrity,” says Merli. “When a corroded rotor or accessory is subject to high g-forces, it can break instantly and cause major damage to the instrument.”
A word about ultracentrifuges
Ultracentrifuges are the most powerful type of centrifuge and therefore require extra attention vis-à-vis safety, and Smith always recommends maintaining a service contract on them. “These beasts are costly and downright dangerous if neglected or mis-handled,” he says. For instance, says Merli, qualified technicians can spot the stress-induced cracking and corrosion in ultracentrifuge parts that users might miss.
Ultracentrifuges should have their oil replaced at least once a year, depending on use. “If you aren’t comfortable doing that, or your particular ultracentrifuge [vendor] recommends that as a service function, then call a service engineer,” says Smith. For safety’s sake, he also recommends adhering to the recommended intervals of rotor evaluations and replacements. “The violence of a rotor coming apart in an ultracentrifuge is something akin to God snapping his fingers,” he says.
Di Francesco compares centrifuge maintenance to good housekeeping. “If you walk into a house and it is in immaculate shape, you tend to treat it with a certain respect,” he says. “I have found that labs who keep their centrifuge tops, and visible parts of the machine immaculate, tend to have less problems [and] are generally in the best shape.” Prevention is the most powerful tool. But, Di Francesco adds, “we all know—stuff happens.”
Image: iStockPhoto