I've got a Quincy 325 turned by a gas engine. When it reaches 125 psi
the unloader works both the intake valves and the engine drops to idle.
A while ago the pressure started to creep up after reaching 125 and I
need to stop it. It's gotten slowly worse over the last year. Took the
valves and unloaders apart and cleaned them up with no change in the
problem. I run this compressor for hours on end for breathing air and
don't want to operate it if it's not working right. Anyone solve a
similar problem?

On 21 Oct 2005 23:32:45 -0700, with neither quill nor qualm,
quickly quoth:

I've got a Quincy 325 turned by a gas engine. When it reaches 125 psi
the unloader works both the intake valves and the engine drops to idle.
A while ago the pressure started to creep up after reaching 125 and I
need to stop it. It's gotten slowly worse over the last year. Took the
valves and unloaders apart and cleaned them up with no change in the
problem. I run this compressor for hours on end for breathing air and
don't want to operate it if it's not working right. Anyone solve a
similar problem?

Since I've never seen the unit, here are two SWAGs:

1) Have you tried adjusting your pressure switch? Knock it down to 100
and see if it still creeps.

2)Are the intakes opening enough to prevent ALL compression, and is
the unloader adjustable for that? It may have worn a bit and isn't
opening them enough.

What does Quincy say about it, BTW?


--
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wrote:

I've got a Quincy 325 turned by a gas engine. When it reaches 125 psi
the unloader works both the intake valves and the engine drops to idle.
A while ago the pressure started to creep up after reaching 125 and I
need to stop it. It's gotten slowly worse over the last year. Took the
valves and unloaders apart and cleaned them up with no change in the
problem. I run this compressor for hours on end for breathing air and
don't want to operate it if it's not working right. Anyone solve a
similar problem?

Is the tank located near a heat source?

Wes

Unloaders aren't opening far enough. Probably the unloader pistons are
sticky, or maybe the pins are worn down short so that the valves don't
lift off the seats much. Or the governor is acting up.
I was 12 years as foreman in a truck/equipment air brake machine
shop. We rebuilt 17,000 compressors in that time. I would estimate that
half of them were there because of governor or unloader problems, both
cheap to fix, but the mechanics tended to replace the compressor, stick
the old governor on it, and then complain that we built crap.
Kind of like alternators and regulators; almost always the
regulator is at fault when the alternator won't charge, but the
electrical rebuilders make lots of money rebuilding alternators that
are perfectly fine.

Dan

wrote:
Unloaders aren't opening far enough. Probably the unloader pistons are
sticky, or maybe the pins are worn down short so that the valves don't
lift off the seats much. Or the governor is acting up.
Dan

I refinished the brass unloader pistons, I thought sticking pistons
might have been the problem, but it wasn't.
The brass unloader pistons stick up about 1/8" pass the top of the
tower where the steel caps sit on them so it's only being plunged about
that 1/8". I thought that was pretty marginal but that's where the
o-ring of the piston tops out on the seat on the tower. There's about
a 1/4" of play on the pins that depress the washer seal so it seems
there might be something up with that, but I don't think the brass
unloader piston has been pounded shorter. I did have to shave some
length off the steel cylinder that the brass unloader sits on in order
to not have to use 3 aluminum gaskets under the tower. It seems the
unloader pistons or the pins ( they look about the same length as new
ones) would have to be shorter. I don't have a new unloader piston to
compare. Which have been the most problem for you?

Adjusting the pressure doesn't change the problem.

The 2nd stage unloader vents fine. The first stage unloader doesn't
vent at all. I thought the first stage pressure cycle was sucked in by
the second stage intake and it vented there. I had both unloader vents
plumbed into the first stage intake tap in the head to keep mud dobbers
from building nests in the tower holes.
Is the first stage not venting a normal thing or is it giving me the
problem?

It's over the gas engine, but it always has been.

The unloader pins should be just long enough that the intake
valves don't touch them while the valves are at work and the unloaders
are retracted. The unloaders should be able to lift the valves far
enough to hold them tight against their upper stops.
Bad governors would either not release the unloaders all the
way, holding the pins in contact with the valves, or would apply the
unloaders slowly. Either way, the pins would get pounded shorter and
the pistons would dance in their bores and wear out the o-rings. The
leaking o-rings would cause a pressure drop in the governor when it
unloaded the compressor, causing it to think that the tank pressure had
fallen and so would re-engage the compressor. It would cycle on and off
every two or three seconds. In extreme cases, the unloaders would get
busted to pieces and the bits would get sucked into the cylinder; end
of compressor.
Sometimes crud would accumulate in the bottom of the unloader
piston bores and keep them from lowering all the way.
If the pressure is creeping up, the valves are able to get onto
or very near their seats while unloaded. You will have to try to figure
out why they aren't being held al the way open.

Dan

Thanks for the help, I'm going to dig into it further this week. The
governor I haven't looked at but I've had problems with everyone of
them, now that you bring it up. Even put a petcock at its low point to
keep the moisture drained from the thing.

Replaced the valves (washers), springs and adjusted the unloader piston
to where it put a little pressure on the pins. I guess there was just
enough wear on the pins and piston to cause the problem. Problem fixed.
Thanks for the help.