Mechanical low-vacuum pumps are very common in laboratories and are used in combination with a wide variety of lab equipment, including rotary evaporators, drying manifolds, centrifugal concentrators, freeze dryers, vacuum ovens, filter flasks and aspirators, desiccators, Schlenk lines, electron microscopes, mass spectrometers, and degassing apparatuses. It is important to choose the correct pump for your application (e.g., appropriately designed and operated vacuum system), maintain the equipment, and protect it from hazards such as liquid ingestion. NOTE: High-vacuum pumps, such as diffusion pumps and turbo-molecular pumps, are outside the scope of this summary.
Taking all necessary precautions when working with vacuum pumps and vacuum systems is essential to maintaining health and safety in the lab while prolonging the life of laboratory equipment.
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Know Your Vacuum Pump
- Familiarize yourself with the types, applications, and limitations of the pumps available. Common types include:
- Oil-filled rotary vane (RV) pumps – Common, good ultimate vacuum. Long lifetime with appropriate preventative maintenance, particularly regular oil changes. Vanes slowly wear but are replaceable by a competent user. Exhaust contains oil mist which is a health hazard. The unit is susceptible to oil contamination from condensable vapors but some types have a gas ballast facility which can partially compensate for that.
- Diaphragm pumps – Moderate to low ultimate vacuum, but oil-free and many types have extremely high corrosion resistance. Available in small sizes; very useful for filtration and aspiration.
- Scroll pumps and screw pumps – Potential alternative to rotary vane pumps, especially where high pumping speeds are required. Consult manufacturers for detailed information on these specialty pumps as they come in many variations.
- Seek manufacturer’s advice on appropriate pump selection, based on application requirements, including:
- Pumping speed and ultimate vacuum required
- Presence or absence of condensable vapors (e.g., water vapor) in the gas stream
- Presence or absence of toxic, corrosive, or oxidizing gases
- Special requirements, e.g., the need for an oil-free environment.
- Read and retain pump documentation, including the operating manual, and make it available to current and future users.
- Understand the operating principles of pump function and settings (e.g., how gas ballast works and when it should be used).
Placement
Several considerations need to be made when choosing a location for a vacuum pump.
- Pumps can require significant power. Plug directly into convenience outlets rather than power strips or extension cords.
- Pumps produce significant heat. Do NOT place pumps in an un-ventilated enclosure and do not store flammable/combustible materials near the pump.
Exhaust
- Pumps shall exhaust into a fume hood or snorkel when a vacuum system is using hazardous materials (e.g., flammable/combustible, toxic, and corrosive).
- An oil mist filter is preferred when oil-filled pumps exhaust into snorkels or other ducting. If not employed, oil may start to pool in the pipework after a few years.
- If NO hazardous materials are being used, the pump may discharge back into the room given there is no other practical option. Oil-filled pumps shall use an oil mist filter if exhausting directly into the lab.
Traps
- Pump traps will vary depending on the materials being used. When using volatile materials, a cold trap shall be used to minimize the mixing of chemicals with the pump oil. Pump oil will degrade over time when exposed to high concentrations of solvents which can lead to pump damage. Another consideration to keep in mind: Pump oil must be compatible with the vapors that pass through the pump (i.e., do not use hydrocarbon pump oil with oxidizing gases or vapors).
- Utilize traps that are appropriately sized and sufficiently cold, depending on the vapors being used.
- Ensure that the glassware is specifically designed for vacuum systems with the ability to withstand the pressure differential without failure.
- Proceed with caution when using liquid nitrogen in cold traps. Withdraw the dewar immediately after the pump is turned off and back-fill the system with air or nitrogen. Failure to withdraw the cryogen may result in liquid air or liquid nitrogen condensing within the trap. Subsequent evaporation of the condensate may cause the system to explode. Furthermore, combinations of liquid air with organic matter greatly enhances combustion/explosivity of the organic matter.
- Mechanical pumps can be greatly damaged by abrasion if particulate matter is ingested. Employ suitable filters in systems where this is a possibility.
Aspiration/Filtration
- A particulate filter with adequate pore size shall be used to block all infectious particles from entering vacuum pumps or house vacuum systems.
- When performing aspiration or filtration, an empty vessel shall be present in the vacuum line, to trap any liquid inadvertently siphoned-up before it can enter the pump or house vacuum system.
- The empty safety-vessel is in addition to the vessel used to collect the aspirate or filtrate as liquid ingestion into a vacuum pump may cause irreparable damage.
- Where demand for a high ultimate vacuum is not required, diaphragm vacuum pumps are often a good choice for aspiration or filtration since they have high resistance to pumping water (or other solvent) vapor.
Pre-Start Checklist
- Power cords and plugs are free of any defects.
- All machine guarding is in place. There shall be no exposed belts or moving parts.
- Any machine part, function, or process that could cause injury must be safeguarded per Cal-OSHA §4184. Refer to the EH&S Machine Guarding Program manual for detailed information.
- An exposed belt is considered immediately dangerous to life or health (IDLH). A pump with a missing belt guard shall be locked/tagged out or disabled in some other way (e.g., by removing the plug) until the guard is replaced.
- Appropriate vacuum glassware is selected and inspected for any visible defects.
- Discard any chipped, scratched, broken, or questionable glassware.
- Avoid flat-bottomed vacuum glassware.
- Pump is placed in secondary containment in case of oil spills.
- Pumps are placed away from combustible/flammable materials.
- Pumps are exhausted into fume hoods, if the materials being used warrant it – see Exhaust.
Waste
- Treat used pump oil as hazardous waste.
- Place a drip pan under the vacuum pump to catch leaking oil.
- Segregate hydrocarbon-based oils from halogenated (e.g., fluorinated) oils.
Maintenance
- A pump-specific logbook or spreadsheet is recommended to track service and routine maintenance, including oil changes.
- Service vacuum pumps based on the manufacturer’s requirements. Lab personnel are free to work on the mechanical components of the pumps (e.g., installing new vanes). However, defer any form of service involving the electronics to a qualified individual or electrician.
- Routine maintenance, such as pump-oil changes, may also be completed by lab personnel. Follow manufacturer recommendations for oil changes or routine maintenance.
- Never service a pump that is energized. Allow the pump to cool completely before venting or servicing and ensure that the pump is manually unplugged and not just turned off. If the pump cannot be unplugged directly, contact EH&S for lock-out/tag-out (LOTO) guidance before attempting to service the pump.
Additional Considerations
- Glassware can be wrapped with tape in a grid pattern or enclosed in plastic netting to help contain glass shards in the event of an implosion.
- When pumps are turned off, back-fill the system immediately with air or appropriate inert gas. This will prevent pump oil back flow into the system.
- Enclose glass desiccators in a cage when under vacuum. Desiccator cages are widely available from laboratory suppliers.