Part 1
Introduction
Welcome
Veneering Basics
14 Good Reasons
Vacuum Press Uses
Vacuum Press Options
Overview
Questions & Answers
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Part 2a (Option 1 of 2)
Project: V2 Venturi Press
About Project: V2
Parts List
Build the Manifold
Build the Reservoirs
Assemble the Venturi
Make the Carrier
Wire the Press
Testing and Adjusting
Mods and Options
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Part 2b (Option 2 of 2)
Project: EVS Pump Press
About Project: EVS
Parts List
Pump Selection
Build the Manifold
Build the Sub-Manifold
Build the Reservoirs
Make the Carrier
Final Assembly
Wire the Press
Testing and Adjusting
Mods and Options
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Part 3
Vacuum Bagging
Vacuum Bag Basics
Polyurethane vs. Vinyl
DIY Vacuum Bags (A)
DIY Vacuum Bags (B)
Connect the Bag
Bag Closures
Bag Platens
Breather Mesh
Maintenance
DIY Frame Press
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Part 4
Veneer Information
About Veneer
Veneering Glossary
Veneering Myths
Balancing a Panel
Veneer Glues
Veneering Tips
Substrate Materials
Flattening Veneers
A Sharp Veneer Saw
Jointing Veneers
Taping Veneers
Dealing with Defects
Curing Glued Panels
Veneering w/o Vacuum
Hammer Veneering
Iron-On Veneering
Veneer Storage
Amazing Bookmatches
Copper Veneer Guide
Paperbacked Veneer
Edgebanding Guide
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Part 5
Miscellaneous Info
Vacuum Press FAQ
Veneering FAQ
Veneer Glue FAQ
Copper Veneer FAQ
Vacuum Forming
Vacuum Chucking
Vacuum Clamping Pedal
Vacuum Clamping Jigs
Vacuum Clamp Matrix
DIY Vacuum Manifold
Vacuum Press Gallery 1
Vacuum Press Gallery 2
Downloads (PDF's)

Information Type: Adjustable Auto-Cycling Vacuum: Electric Pump Page: 3 of 11

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.
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.
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. To the best of my knowledge, there is no way to contain the oil smoke. 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.
Rotary vane pumps are designed to run continuously. This type of pump is not suitable for the Project: EVS vacuum press system. This is especially true of Gast 0522 and 0523 pumps. These vacuum pumps have been a nightmare for me. I have found them difficult to fine tune for vacuum pressing and they draw a tremendous amount of power when they start up. I am well aware that several other companies are using rotary vane pumps for their vacuum press systems. If you are using a rotary vane pump, you will at least need the relay and vacuum damper parts along with your EVS kit. I offer ZERO support for troubleshooting vacuum press systems built with rotary vane pumps. If you try to use this kit with a rotary vane pump, please know that I will not be able to help you troubleshoot problems. These pumps are notoriously difficult to adapt to vacuum press use due to electrical issues.
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.

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.