Using a vacuum pump to boost an air compressor?

Wondering if I could hook the outlet of a vacuum pump to the inlet of an air compressor to increase flow rate of air to the tank.

I’m just trying to get a decent concept of why it won’t work before I try it. I assume that I’d need a vacuum pump with CFM that’s at least close to the CFM rating on my compressor.

I’m thinking it’s gonna be sucking oil vapor from the vacuum pump but I can probably fix that just by hooking a condenser inline and returning the oil to the vacuum pump… reason I’m wanting to do this is I need a higher CFM than what my compressor can provide me if I want to use my plasma torch. Otherwise I’m looking at getting a new compressor and I’ve already got a couple vacuum pumps that are pretty close in cfm rsting to my compressor.

I’m not worried about making a complicated setup, I won’t be cutting steel very often so it’s worth the savings to me.

A diaphragm vacuum pump is essentially an air compressor with the flow reversed and fed into a tank.

But it’s more complicated than that, always


I’m talking about specifically using a vacuum pump for the purpose of increasing the air pressure to higher than atmospheric on the inlet port of my splash lubricated air compressor.

I assume there will be some degree of “efficiency” increase but it couldn’t be utilized unless the air compressor could keep up with the volume the vacuum pump is producing. I can see maybe the restriction on the outlet for the vacuum pump causing some trouble, but then again the E2Mx series of pumps from edwards don’t seem to have trouble coping with the restrictions on the outlet when an oil mist separator is attached…

Idk I think I’m overthinkinf this.

Just… get a bigger air compressor.


It depends on the pumps. A reciprocal pump with atmospheric pressure on the inlet will put out one cylinder volume per stroke at 100% efficiency. If the inlet is under two atmospheres pressure, it will put out two cylinder volumes per stroke.


A far better solution would be adding an additional head to your compressor like this.>%20Air%20Compressor%20Parts%20%2B%20Maintenance%20>%20Air%20Compressor%20Pump&utm_campaign=NorthStar&utm_content=4592900&cmpid=53403368&agid=3200075880&tgtid=pla-4577404347715287&prdid=4592900&msclkid=255af01d89e61b7dbf00907367f845c2&gclid=255af01d89e61b7dbf00907367f845c2&gclsrc=3p.ds


Yeah, what he said.

Using a vacuum pump with its intake open to atmosphere as a pre-compressor compressor is just being cruel.

Use a damn compressor for that trick.


If you can’t afford another compressor and aren’t going to be cutting steel that often or for very long, you could use a large surge tank and start it at as high a pressure as possible. IE: A plasma cutter will operate at 90 psi, so if you started at 125 psi in a large tank, it would be a matter of time before the compressor output and reserve decayed the pressure below 90 psi.

Not sure what torch you have or how thick you are trying to cut, but the smaller the orifice the less air consumed, so you might use a smaller one where possible, when operating at maximum pressures.

You could also plumb two small compressors to a large holding tank to keep up with a plasma torch running 120 psi @ 4 to 8 scfm.

What I would suggest for low capital investment and great performance is just use bottled air or nitrogen and a regulator when using your plasma torch.


Rotary Vane, Dry Scroll, Diaphragm and other lab pumps do not tolerate any back-pressure on the outlet.


Good point when using them as a vacuum pump, but all are also compressors on the discharge side when their inlets are full open.

The rotary vane and dry scroll pump designs are used as superchargers, which put out high flow at an atmosphere or less boost.

To double the output of the secondary compressor, the first pump would have to maintain 15 psi pressure on the second pumps inlet. That means it puts out twice the rated output of the second pump while maintaining 15 psi.

As an aside, the way to throttle a blower for least horsepower usage is on the inlet side, so that the impeller is operating in a partial vacuum versus in compressed air when throttling/deadheading the discharge side.


Bottled nitrogen is also dry, saving you from needing an air dryer to protect your consumables and work piece.


Also a good point!

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I think you are over thinking this. You just need a bigger air compressor. How much CFM and what pressure do you need?


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