Ignoramus16649 wrote:

It takes about 1-2 minutes for unloaders to unload enough so that the
compressor can restart. Possibly, this is wrong. I do not know.

In practice, this should not be an issue, as going from full tank to
restart should take more than that, but still it may indicate that
something is wrong with unloaders.

Doesn't your Quincy have pneumatic unloader diaphragms on the intake
valves? You apply air pressure to these diaphragms and a pin drops down
to keep the intake valves from closing. When the compressor is up to
speed, something (electrical, pneumatic or oil pressure) cuts off the
air to the unloaders, the pins retract, and the compressor starts
pumping. It sounds like you are talking about an unloader in the
delivery line to the tank. When it bleeds off pressure, it has to
remove all the pressure in the whole compressor, including the high
pressure cylinder and intercooler. This is kind of the hard way to
unload a 2-stage compressor.

I have a smaller one-stage Quincy, and rigged up an electronic dual-mode
controller for it. It unloads until the compressor is up to speed and
has oil pressure, then unloads when the tank pressure is at the set
point. It keeps the motor running until either more air is needed or a
minute has elapsed. When the motor time elapses, it shuts down with the
valves unloaded, so the compressor stops smoothly, without a
chug-chug-chug. The control also shuts the compressor off if it ever
pumps for a full 10 minutes without ever filling the tank, or if it
loses oil pressure.

Jon