The unloader valve should release the pressure from the output
line of the compressor as the compressor turns off. If you don't
hear the air release, that valve is not doing its job.

Bob

"Tom" wrote in message
news:Hebgd.17323$HA.14609@attbi_s01...
John
When it shuts off there is no hissing noise. It's just quite.

"John Beckman" wrote in message
...
"Tom" wrote in message
newsk7gd.321434$MQ5.224771@attbi_s52...
I have a Sears 25 gallon/4HP horizontal compressor. When I
first turn it
on
it runs fine and shuts off at 150psi. The problem I have
is when the
pressure gets at the level where it automatically kicks on
again it then
pops the breaker off and I then have to reset the breaker
before it will
run
again. I have a dedicated 20 amp circuit with 12/2WG using
a Square D
breaker and a 20 amp duplex receptacle for the compressor,
and nothing
else
is on this circuit. Do any of you folks have any
suggestions as to how I
can
cure this problem? Thanks for your help.


Tom, does the compressor make a loud hissing noise after it
shuts down at
150 psi? This would be the "un-loader" valve. The unloader
allows the
compressor to start with little of no pressure in the
cylinders. This
allows
for a low starting amps until the compressor gets up to
speed. If the
unloader is not working, then the full system pressure is
adding
resistance
to the starting load and may be too much for the breaker.

john