EW wrote:

My OLD 220 Volt Sears air compressor (model # 106.15378) with twin cylinders
recently quit being able to compress more than about 65 psi into the tank.
At that point, the motor still runs, the fan belt starts to squeal, and the
cylinders will no longer run. I can't even "turn" the flywheel by hand.
Lowering pressure a lot lets it run again.
I'm assuming something (reed valve??) is causing the high pressure air to
"work" against the cylinders so hard that they will simply not pump. (I
wonder if storing the compressor in my hot Texas shop -- 140 degrees in mid
PM -- contributed to this!)
Any ideas? "IF" it's a reed valve, is it accessible at the top of the
cylinder block? Is there a difference between the "input air" and output
air" reed valve? Can I fix a reed valve? ANY comments would help!!
Thanks.

EW
you have two valves in almost all compressors:
one is the load valve, after the compressor pumps up and cuts off the
machine makes a whew sound.. like air escaping for a few seconds..its a
blast... that is to take the load off the head so it can start pumping
next time when it is time for the compressor to go again....
the other valve is the check valve.... it stops the air from coming back
from the tank back to the compressor.. it holds the air back so the
motor can turn the crank...... a new check valve cost about $15.00
yours might be leaking and when getting up to 65 lbs. it will not hold
back any more??? if that is the case(when mine went bad it would blow
out the fuse for the elect. service.... was drawing about 50 amps. or
more............ is your belt tight??? do you have oil in the
compressor?? too much oil??? how about taking the larger tubing off
where it goes into the tank(the check valve is right there..where the
tubing goes into it... and run the compressor.. it will not go up in
pressure as the output of the compressor is just pumping air into the
atmosphere and not into the tank... let it run for the same amount of
time and see what happens...does it slow down??? or kill??? if not that
its the check valve... if it still slows down or kills then its the
pistons in the cylinder block that are swelling up due to friction and
you might have problems????? hope for the best... either sears or any
pump replair shop can sell you a check valve... the unloader valve at
sears is part of the whole diaphram valve that controls the pressure
from the tank.. i could not get one from sears.. you had to buy the whol
thing.. so i went to a pump repair place.. they fix air compressors and
got one there for about $15.00 also... these valve are pretty standard
sized and interchangable for most compressors... hope this helps.