Compressor Q's

Assuming that you paid next to nothing, congratulations on the deal and the fun times ahead. :)

there are usually little thin copper lines running from the heads to the motor switch or some such.

not sure, but you can always buy a different motor switch.

good idea

I think that they pulley fans should work fine with shrouds, also.

The unloader is usually part of the check valve located in the outlet area, there's a small copper tube that runs to the pressure switch on the installations I've seen, usually around 1/8" copper or so, to actuate it on compresssor turn-off. The check valves w/pressure relief and the pressure switches are readily available, run about $20 or so. For motors above about 1 hp they usually put a contactor or relay in the circuit, the pressure switch contacts aren't that hefty to start big motors directly.

As to the sound, if it's got a hiss, it's the unloader. If no hiss, might be the contactor dropping out. Big ones tend to be noisy.

Stan

Exrtrapolating from well pressure-switch knowledge, one of the springs might only contact whatever moving part is in there when its close to shutting off.

On my well switch, one spring adjusts at the same time the "on" pressure and the "off" pressure, the other one acts like a 'booster- spring' to affect only the off pressure.

Dave

Well, these are HEAVY duty compressors, built like a tank, so that is to be expected. Parts are still available, and the few things I needed (filters, mostly) seemed reasonable. The local dealer has all the maintenance documents going all the way back to the 1960's.

They are diaphragm-operated plungers over the intake valves, that are operated by air pressure through a copper tube. (That applies to Quincy, others may be different.) They are quite obvious if you know what to look for, and will be sitting on top of the cylinder head(s).

That may be an unloader on the pressure control swich, which is entirely different from valve unloaders. With valve unloaders, they do their stuff at the start of the compressor run, and you can hear the "tone" of the compressor change dramatically a second or so after it spins up, when the unloaders de-activate, and the compressor begins to suck air and compress it. Quincy has a couple of different systems for opeating the pneumatic unloaders. The cheap one is an air pressure-controlled valve that turns the unloader on and off to control pressure, and the motor runs continuously. Then there is a more complicated one where pressure is controlled by starting and stopping the motor, and the unloader de-activates when oil pressure in the compressor comes up. It has a delay, also.

Most pressure switches DO have a way to adjust "differential", although it may be FAR from obvious. But, usually, there are two adjusting screws, however one may be WELL hidden.

Jon

My Qs have the unloaders operating like this: Oil pressure moves a valve that supplies air pressure to a diaphragm that deactivates the unloader. No oil pressure, unloader doesn't deactivate.

We just have a cheapie pressure switch activate magnetic starters. It's set at 90-120. Those Quincys will last forever...unless you let Iggy hot-rod them.

I still have overhead line shafts but they don't run anything anymore. All the babbited bearings are still smooth as silk.

I think that my "hot-rodding" of my compressor -- putting a 5HP motor on it -- would actually make it last longer.

A couple of things to start with.. the pressure switch isn't a regulator. A regulator is a non-electrical part.

The pressure switch settings don't govern starting load, as the term unloader applies.

You'd be wise to get the manuals for the compressors. You'll be able to determine if the pumps have mechanical unloaders for no-load starting, with the manuals in front of you.

A pressure unloading method used on many compressors utilizes a small diameter air line from the head outlet cavity to a small unloader valve that is opened by a lever sticking out of the pressure switch (when the switch reacts to the high pressure cutoff limit). The reason air doesn't continue to bleed out the little unloader (air) valve, is because the tank air is held by a check valve (sometimes located at the pump outlet line connection to the tank/receiver).

Some industrial duty compressors have mechanical unloaders integrated into the pump head design.

WB metalworking projects

The headers were a dead give-away...not to mention the chrome intake.

on my Quincy, the original unloader was operated by oil pressure and had copper lines running to the compressor heads - that seemed to not work properly, so the place I got it from sent me a check valve and an unloader that was part of the pressure actuated switch. I would suggest keeping the belt shroud in place - you won't be happy if your shirt gets wound around the pulleys with you in it.

"Proctologically Violated©®" wrote in message news:%wAKh.844$ snipped-for-privacy@newsfe12.lga...

On the QT-25 Quincy that I used to maintain had the unloader control down between the motor and the compressor body. Quite easy to set the load and unload points as well as switching from unloader mode to on/ off mode for motor control. Boss was pretty skeptical that I could save them several hundred bucks a month on power by running the compressor in unloader mode when we were running production and using on/off mode when we really didn't need air in the shop...You'd be suprized at how much one could save by keeping that 25hp motor in the unloader mode and only starting it once a day.

Craig