Noisy check valve - custom installation

by Jim Croghan
(Wilmington, Ohio)

I am paralleling two compressors. One is an 80 gallon 175 psi "shop" compressor and the other is a small 20 gallon 125 psi homeowner unit.

The big unit is too big to run on our backup generator. So, I'd am paralleling the two units into the shop air distribution system and wiring the big compressor to the utility power only electrical panel and the small compressor into the utility/gen set protected sub panel.

In the event of a utility power failure, the big compressor will not run.

When the air pressure falls below the 70 psi trip (on) point for the small compressor, it will charge the system to 125 psi. (Compressed air is needed for our waste oil furnace and of course the automotive repair).

I bought a NAPA 82782 1/2" check valve to install on the OUTPUT of the big compressor tank in order to isolate the tank from the rest of the system.

I didn't want the little compressor trying to charge up the big tank. The little compressor also has a check valve to protect it from the high pressure of the system under normal operating conditions.

The problem is that the 1/2" check valve "squeaks" really loudly and is very annoying as air is drawn from the big tank out into the system, especially when a small quantity of air is bring drawn (like our furnace). The noisy sounds like an old windmill turning slowly in the wind with a bearing that hasn't been greased in 30 years.

So the question (finally) is do you have experience with "new" check valves that are noisy during operation?

Comments for Noisy check valve - custom installation

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Feb 15, 2019
I agree
by: Jim

Yes, this needs to be automatic to provide compressed air for the waste oil furnace over the unattended nights and weekends during the winter.

Interesting thought on the cracking pressure. I wondered about upgrading the spring in the NAPA check valve (it's serviceable). I may try that. I'm going to try to contact the NAPA air folks and see if there is any information that way too.

Thanks for the ideas! I'll post again after I make some changes.

Feb 14, 2019
by: Doug in

I suppose you'd like this to be automatic, and there is a solution in the form of a solenoid or pressure operated valve, but it ain't cheap - $400 or so. Next would be just replace the CV with a ball valve and work it when the power fails.

But I think a big chunk of the problem is low cracking pressure, which I don't find spec'd on that NAPA valve.

So maybe this would work better - 5 PSI cracking, which hopefully would give you bursts of pressure with a thunk rather than a squeal.

...and then change the size to 1/2" or whatever.

Feb 14, 2019
by: Jim

Thanks for the reply Doug. Yes, the simple problem is the check valve is noisy during periods of air flow.

Actually, the less air flow the worse the noise is. When the waste oil furnace runs the noise is a quieter constant noise like a muffled low pitch hydraulic screech. When the furnace shuts off and the only draw on the air supply is a heated parts washer "bubbler", that's when the noise is like an old windmill or an electric solenoid type buzz.

I agree with you that the noise is in the valve and valve seat. It also seems to be probably tied into the spring tension too (since CFM has an effect).

There was a place to put photos on the original questionaire, I'll see if I can post a diagram.


Feb 14, 2019
Check valve?
by: Doug in

I got a bit confused reading how this is set up.

If I understand, the essence of the problem is you have an air source with a check valve that makes noise when there is a draw.

Is the below a fair representation of your set-up:

(service/distribution piping)
+Tee --|
where If so, the problem is it's brass, and probably a brass seat.

If I were you, and would rather not or could not return it, I'd disassemble it and try just a smidge of a dry lubricant on it.

I have more thoughts, but let's get this part out of the way first...

Let us know.

Oh, and what load causes this noise, and about how much (CFM) is it and for how long? Is the cause of the noisy, low load times a regularly scheduled draw or a random/as required kind of thing?

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