I have been cleaning up this Quincy install by properly tucking cables
into conduits, wiring things correctly, using crimped terminals where
My Quincy compressor comes with a nice old Size 2 electrical control.
The nice thing about it is that overloads are adjustable by turning
little knobs, so I do not have to buy overload heaters. At 220v, it is
rated at up to 15 HP. The motor I have on the compressor right now, is
The compressor was wired for 440 volts originally and had a 7.5 HP
motor (much bigger than my current 10 HP motor). So the overload setting
that it had set, obviously would not match. For for the first few
weeks I did not use overloads by bypassing them, but now I want to set
The question is what is "properly".
My thinking is that in this context, it means that the compressor can
reliably restart at the restarting pressure (100 PSI or so), but at
the same time, overloads should pop in a second or so if the motor is
I can reproduce a stalled motor very easily, by stopping the
compressor when there is pressure in the tank, and restarting within a
minute, before unloaders bleed enough air. (I hope that it is not an
indication that something is wrong with unloaders, a separate topic)
I already set the overloads, apparently high enough so that they do
not pop when the motor is running regularly. So, therefore, to me the
procedure now would be to turn them down, to the point when they
reliably pop on a stalled motor, but when compressor still starts
Am I missing something and is that too unscientific?
"Ignoramus16649" wrote in message >
There may be a more scientific method, but that's what I have always seen.
Even the adjustable breaker on 150 HP pumps are often set by "experience".
Set it just high enough for normal operation, and if it ever fails
prematurely just bump it up a little.
What restatarting pressure??? That's what unloader valves are for, it's
not supposed to restart under pressure. If it takes any amount of time
for the unloaders to unload, I'd examine them closely as I think they
should be near instant.
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.
With overload adjusted properly, the worst case outcome would be the
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.
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.
The idea of an unloader is to let the pump start w/o the resistance of the
pressure in the
tank. Then after you have the pump, motor, and pulleys at full speed, connect
output to the tank.
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller
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
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.
Except if you are running it from a VFD (IIRC, a VFD was
somewhere in the equation), you really don't want the overloads popping
between the VFD and the motor -- and the VFD itself should perform the
function of the overloads as well.
As long as you are running it from three phase from a rotary
converter, yes you want the overloads.
I have more or less changed my mind, and am feeling rather good about
running it from a phase converter. It is quiet and reliable. If I
would run it from a VFD, which is still a possibility, I would not use
that motor starter for any purpose.