Compressor doesn't run air tools well

by tom

Compressor builds pressure easily but doesn't run air tools well

Bought a used twin reciprocating compressor 7 HP 110 tank from an existing shop.

The compressor builds pressure easily to 95-100lbs. A 1/2" ID line run from the outlet of the compressor to reg/filter to swirl air drier to another swirl drier to a regulator to a 3' desiccant drier(now empty) to a 1/2" ID air line(50' long).

This 1/2" line runs directly to a blast cabinet or is knocked down to 3/8-1/4 line to run air tools.

The flow of air is weak. The air flow builds to what can run a tool about 15 seconds before the compressor will kick on. As the compressor builds pressure the tool begins to slow down as if there is no pressure or cfm in the tank.

There are no leaks in the lines. Leave the compressor full overnight w/o power and the pressure is maintained.

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May 14, 2015
air flow
by: Doug in

Where to start...
OK, so this sounds like the opposite of what happens when you have a blown head gasket that only lets go when the pressure is near cutoff...

The question remains: was the distribution system existing, and this new(ish) compressor was grafted on, right? And before that, it was working as expected?

And the system looks something like this:

Compressor...110CF tank...15ft copper...dripline...reg/filter...1/2in pipe...tool station(s) with reg and/or filter(s)...more 1/2in pipe...blast cabinet

What I'd want to know is what the pressure is not only at the tank, but also along the line at the tool stations.

I suspect that one or more of the fittings has loose pipe tape or something flapping in the breese through the pipe, closing it off, limiting flow. Watching the pressure along the pipe with the blast cabinet on and off should clue you to where the blockage is. You want a pressure gage on the pipe or close to it, with the regulator wide open.

Maybe you could post some pix of what your setup looks like?

Good luck.

May 12, 2015
Follow up info
by: Anonymous

While the blast cabinet is running, no other tool is on line.

What is so crazy is that whether I run the blast cabinet(50psi) or a jitterbug or orbital sander, the tools run very slowly.

As the tank begins to loose pressure and cfm, the sander starts to pick up speed and begins to run well.

It runs to speed 10-15 seconds before the compressor cycles again.

As pressure is built, the tool begins to slow down again until the tool stops. Keep the finger on the trigger,hear the air slowly blow out of the tool, and then it picks up speed. 10-15 seconds later, compressor turns on and the tool looses power.

The tools are well maintained and oiled regularly.As the compressed air exists the tank, I have a 15' 1/2" ID looped copper line, to act as a cooler/condenser.

Before it enters the first regulator, I have a drop down in 1/2" black pipe with a ball valve to catch and released moisture in the line. When I bleed that valve, high volumes of air, under pressure, are released. So that path is clear.

I checked to see that all the other checks down stream are air in/air out. I can bleed each regulator or separator and air comes out, but its hard to tell since their valves are small.

I am reluctant to start removing each or everyone of these regulators/condensers since they are all plumbed up with high pressure plastic pipe.

May 12, 2015
pipes and tanks
by: Doug in

"Bought a used twin reciprocating compressor 7 HP 110 tank from an existing shop."

Is that 110 cubic feet or volts?

If volts, what's the tank size?

Is this a replacement compressor for an existing installation?

May 12, 2015
doesn't run air tools well
by: Bill

Your compressor should generate around 30 CFM of compressed air at 90 PSI.

What you don't say is what the demand of the blast cabinet is, and if the problem persists even if the blast cabinet isn't running.

If the problem is there even without the blast cabinet running I would suspect a bum regulator, or, you've got so many areas affecting flow that you are getting significant pressure drop (see the page on pressure drop for specific info) which is preventing the air from getting to your air tools in enough volume to drive them.


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