Bob Engelhardt wrote:

I have an IR home-shop compressor (20 gal, 1 1/2 hp) with a leak. I
just measured & timed it: in 17 hours the pressure dropped from 100 psi
to 55. This means the compressor runs several times a day just to
maintain pressure. It is loud, so this is annoying.

In an attempt to find the leak, I sprayed soapy water on EVERYTHING: the
entire tank, the drain fittings, the "Christmas tree" fittings (pressure
switch, guage, etc). I even disconnected the pump output line to see if
the check valve was leaking back into the pump. I found a small leak in
the pressure guage connection, which I fixed (tightened). It STILL
leaks (but not the pressure guage)!!

Now it has become a challenge. I've GOT to find that leak! Before I
start taking parts off to eliminate them as leaks, does anybody have any
tips/tricks for finding leaks that might save me the work?

Thanks,
Bob

Well it seems like you've isolated it. If you've plugged the tank
outlet,
and the "christmas tree" checks out, it must be the non-return or check
valve between compressor and tank. Once removed, they're not a biggie to
test.

Tom