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About lost pressure

by Without Air
(Kentucky)

Hello. My compressor runs all the time now and doesn't achieve full pressure.

This started occurring after I drained the tank and replaced the oil. It doesn't appear/or feel like it's leaking anywhere but with the shroud off and the fan running, and noise, it's impossible to know where my trouble is.

I have a central/neumatic 120psi compressor with a 21 gal tank.(harbor freight}cheapo.

It was working before I drained and changed the oil. The level had always been fine.

It was extremely cold out then too. But now after it's warmed up in the garage, the pump still always runs and the pressure never gets over about 60 psi.

Where should I start? switch or piston? any advice is appreciated. Thanks.

P.S. I planned on changing the regulator assembly (upgrade) for better constant control.

Comments for
About lost pressure

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Feb 21, 2008
 Ongoing Lost Pressure
by: Bill - Publisher

Peace to you too, man. Something this 'ol world could use a lot more of these days.

To restate the obvious. if you had debris in the drain cock of your compressor tank, you'd hear it bleeding off once the compressor motor was off.

OK, you've convinced me. It might very well be the pressure switch.

There's some here if you want to try and get a new one.

Good luck and I look forward to hearing from you again.

Bill
Feb 21, 2008
 Lost Compressor Air Pressure continued....
by: Anonymous

Thanks Bill.

I have a switched dedicated 30 amp service to my compressor.

When I turn off the switch i'll listen with my engine stethescope/after it warms up outside.

As I recall though there wasn't any noticeable audible clue, nor could I feel any air leaks. The unit used to quit at 120psi. Currently top pressure is around 50-60psi without ever shutting off.

It's real possible that there is some tank debris caught in the bottom drain hole,allowing air to escape, since that was the only thing touched aside from pouring oil into it after it was drained.

Thanks again for stating the obvious. How many times in troubleshooting do we wind up back at the basics.

I'll post later this spring.

The forum is nicely laid out and easy to navigate.

Peace.
Feb 19, 2008
 About Lost Compressor Pressure
by: Bill - Publisher

Dear Without Air:

The compressor pressure switch has a cut in and cut out pressure.

The cut in pressure turns the compressor pump on when the pressure in the tank reaches that low pressure set point.

The cut out pressure turns the compressor pump off when the pressure in the tank reaches this high set point.

It seems logical then, that if the compressor is turning on when the low set point is reached, and the compressor starts to pump air into the tank, that eventually the tank pressure would reach the cut out pressure point and the compressor pump would stop.

Yours doesn't. You didn't indicate how high the pressure achieved was.

It's my opinion that you either have an air leak that's bleeding air off faster than your compressor pump can generate it, or somehow the seals around the piston(s) have been damaged, and you are getting blow by. It's more likely the former than the latter.

When your compressor is running, pull the electrical supply plug to shut the compressor pump off so you can hear, and listen for air leaks.

Make sure the tank drain stop cock is closed tightly.

I don't think it's your pressure switch as it's clear the low pressure point is turning the compressor on. The high pressure point isn't being reached, so the pressure switch can't turn the compressor off. If you can adjust your high pressure set point, lower it to below the pressure that your compressor is generating, and see if the unit shuts itself off.

Hope this helps. Oh, and upgrading your regulator may not be necessary if your air using application can "live" with a 3-5 PSI pressure range. If you need a tighter pressure window than that, you'll want a precision regulator. Here's a bit information on regulators.

Cheers,

Bill

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