A while back the check valve on my main air compressor died. I took it
out, took it apart, cleaned it up, and threw an o-ring in it as a
temporary seal and repair. Its worked great. On Friday I noticed a
slow leak after I shut everything down. The sound was coming from the
pressure switch and unloader valve assembly. I ordered a new pressure
switch to be delivered today and forgot about. Yesterday I was in
Nogales picking up a load of steel plate anyway, so today was fine.

Oh, yeah. Side brag. I'm sure you guys all get it cheaper, but one
piece of 4x8x1/4 plate from the local Remington Industrial was $240 give
or take. I found some in Nogales for 135 for the first piece and $100
for every additional piece. I don't need that much right now, but I
bought ten pieces to make it worth the trip. If I have it I'll use it.

Back on topic. As I was walking out to the compressor it occurred to me
that my o-ring band-aid might have failed and I had ordered in a
pressure switch assembly for nothing. So with pressure still hissing
out of the pressure switch I unplugged the hose from the top of the
check valve that goes to the unloader and checked the fitting with my
thumb. No air leaking and the hissing from the pressure switch was just
as loud. In fact much louder than on Friday.

Now an odd question. Probably a dumb one at that. What is an air
compressor pressure switch with 4 ports intended for? When I was
shopping for one I saw single port and 4 port models. Both were under
$20 in generic brands and not much more for name brands.