Bostitch 4 Gallon CAP2040 Won't Build Pressure After Fix

4 Gallon Pancake Oil Free Air Compressor keeps running. It would not build beyond 20 PSI. Does not shut off.

Opened it up and saw one of the reeds/flapper on valve plate was broken off.

I replaced the Valve Plate Assembly, reed and also the Intake Valve.

All the other parts look great.(Gaskets, cylinder, piston ring, little air filter and head)

It now will build to 50 PSI and keeps running. If I come back 2 days later, it still has 50 PSI inside tank. Its not leaking at all.

I have disconnected nylon tube (Bleeder tube?) from tank port/check Valve and no air escapes out of tank.

I also disconnected outlet tube on both ends and no air escapes. Both of these tubes can be disconnected for days and no pressure loss in tank.

What else is there to check for why its not building pressure beyond 50 psi.

I also have made sure it is plugged directly into a 20 amp outlet for full power supply.

Pressure reducer valve is tightened all the way.

I have read everywhere on this site and all the problems seems to be reeds/valves, gasket or air leaks for why there is no pressure being built. None of these are my problems. Thank you for your time.

Comments for Bostitch 4 Gallon CAP2040 Won't Build Pressure After Fix

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Feb 02, 2016
Compressor pump head
by: Bill

There's a torque guide on this site, but essentially, make sure all bolts are tight.

If it were an electrical issue, the motor would get really really hot and, perhaps, go off on thermal cut out to protect itself. That doesn't seem to be happening.

Sure, it could be the capacitor, so use a multi-meter to check that if you wish. See how on that page on this site.

If you've followed all the checks on the troubleshooting page about why air compressors won't build pressure, and you've replaced the valve plates, it's pretty much got to be a gasket failure, or maybe your piston seals.

Do you get air bleeding out of the oil fill tube cap when it's running?

Feb 02, 2016
Bostitch 4 Gallon CAP2040 Won't build pressure after Fix
by: Jennifer

Thank-you Bill,

How do I know if the pump head is torqued Satisfactorily?

The Gaskets looked perfect. But you think replacing them is needed?

Wondering if there is a way to test the power of the compressor with a multi-meter. Does that sound like something that could cause it not build pass 50 psi?

Feb 01, 2016
Bostitch 4 Gallon CAP2040
by: Bill

That is now gets to 50 PSI after your fix suggests to me that your pump gasket is letting go at that pressure.

You didn't indicate that you had replaced the gasket when you replaced the plate.

Make sure the pump head is torqued satisfactorily, and if the Bostitch problem persists, I'd pull the pump apart again and replace the gasket, if it were my compressor.

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