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Information
Type: Adjustable Auto-Cycling
Vacuum: Electric Pump
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Selecting A Vacuum Pump
Speed and Maximum Pressure
 Vacuum pumps are often rated on the flow capacity which is stated as CFM (cubic feet per minute). This references the speed at which the pump is capable of moving or removing air and is most often measured at zero pressure. A pump rated at 1 CFM will be fine for flat panel work on vacuum bags up to 4' x 4'. For bags up to 4' x 8' a 3 CFM or greater pump is needed.
If your vacuum press will be pulling down curved veneer forms or bent laminations, the general rule of thumb is that the pump must be three times faster. This means that a 3 CFM or greater pump is best for vacuum bags up to 4' x 4' for this type of use. Why? Because there is, on average, 3 times more free air inside of a bag containing a bent lamination than there is inside a bag containing a flat panel.
Vacuum pumps are also rated by their maximum achievable vacuum level at sea level which is often expressed as inches of mercury or "Hg". For vacuum veneering, the minimum acceptable level of vacuum is 18" of Hg. The ideal vacuum level though is 21" of Hg. At the high end, the maximum level of vacuum for veneer work is 25.5" of Hg. Anything over this amount is not only overkill, it's also harder on the pump. Additionally, extreme vacuum levels can cause the veneer to develop small pustules of glue on the veneer face.
Types of Vacuum Pumps
The next consideration when building a pump based vacuum press system is the pump style. Here are the some of the options:
- Diaphragm pumps are very quiet and durable. This type of pump is oil-less and usually has a small footprint. They are ideal pumps for a vacuum system. Typical CFM rating is 1 to 3.
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- Piston pumps are not as quiet as diaphragm pumps, but are just as durable. They are almost always oil-less and also work well for a vacuum press. Typical range of CFM is 2 to 5.
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- Oil bath pumps are less noisy than piston pumps but not as quiet as diaphragm pumps. This type of pump has a tendency to emit a plume of oil into the air. For most users, this can be a huge issue that causes problems with the finish that is applied to the veneered project or any other unfinished project in the vicinity of the pump. This type of pump requires occasional oil changes and can draw a large amount of amperage. Usually, these pumps range from 3 to 6 CFM.
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- Rotary vane pumps are available in oil-less and lubricated styles. They are generally maintenance free but they get very hot during use. This can create a serious issue if the thermal protection circuit kicks on while your press is in use. It's a good idea to have a standby unit on hand in the event that the rotary vane pump overheats. Typical CFM range for this style of pump is from 5 to 20. If you choose this style pump, you may need a relay to do the high current switching for the vacum controller. These pumps are notoriously difficult to adapt to vacuum press use due to electrical issues.
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- Refrigerant compressors can also be used for limited runs of vacuum press work. They are quiet, but slow to pull a full vacuum. Typical CFM is less than 1.
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Vacuum Pump Manufacturers
The most common names in vacuum pump apparatus are Gast Manufacturing and Thomas. Both companies offer very refined pumps in a wide range of models. Other manufacturers include Alcatel, Edwards, Sargent, Welch, Busch and Leybold. These particular manufacturers offer high end, industrial, or scientific-use vacuum pumps.
Restart Pressure
 The pump's ability to restart while under pressure is not a factor in selecting a model for vacuum pressing. The Project: EVS system uses a sub-reservoir and Mac valve assembly to unload the vacuum from the pump's intake port. Even if the pump you have selected can restart under pressure, it's a good idea to vent off the pressure after each cycle.
"Regardless of the restarting capability, pressure should always be released from the system to maintain proper life expectancy of the internal valves in each pump. This is true for all pump models including piston, diaphragm, and rotary vane."
- Gast Manufacturing
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