"Ignoramus16649" wrote in message
...
On 2009-03-04, Buerste wrote:

Mine unload the heads in less than 2 seconds. When they start, the
unloaders stay open for three to four seconds. Yours looks the same with
a
diaphragm forcing the valve open until oil pressure shuts off the air to
the
top side of the diaphragm.

I have almost no clue as to how unloaders actually operate on the
QR-25 head. Do you know anything about it, I will be eternally
grateful for any info.

--


The top of the diaphragm on top of the valve is supplied air pressure from
the tank side. The diaphragm pushes down on three pins in the valve body
and prevents the disk valve from seating. There is an air valve on the air
tube going to the diaphragm. This valve is operated by oil pressure from
the running compressor. Therefore, no oil pressure = air valve open =
diaphragm unseating disk valve. If there is no air pressure in on the tank
side, the disk valve will seat letting the compressor pump air. If the oil
pressure is up, the air valve is closed letting the disk valve seat and the
compressor pump.

This is a good set-up, if the oil pressure fails for any reason, the disk
valve won't seat and the compressor won't get damaged from no oil. Not
fool-proof, but good!

The diaphragm is reinforced rubber and does wear out, be warned.