It takes time for the oil pressure to bleed off. As it is coasting down, the oil pump is still turning and making pressure, so the pump will not unload until the compressor has come to a full stop and oil pressure has dropped to a point where the hydraulic unloader can retract and let air through. It will not freewheel down without pumping, so expect it to stop fairly quickly, then you will get a blast of air out of the side of the unloaders as the piston pushes down on the pins and blows down the cylinders.
I am familiar with Quincy Rogers Northwestern, as I saw their tag on a 1971 150hp Quincy QSI rotary screw in northern Saskatchewan back in the mid 90s. The compressor was 25 years old and still humming along happily. Probably still is.
Quincy is headquartered in Bay Minette Alabama now, so I am surprised that it is so hard to find a dealer.
THANK YOU so much for spending the time and holding my hand through this
!!!
I bought my QR-350 at a local auction from a metal fab shop that made pressurized tanks (similar to what the compressor is sitting on and much larger) so it was rode hard and put away VERY wet and dirt for many years with them.
When I brought it home it was filthy and I didn't have the reserve power in my electrical panel to install it, so the compressor just sat for at least a year before i got it hooked up. When that time came, I hadn't paid attention to what the nameplate voltage was on the motor so I didn't have my electrician install a Buck/Boost Transformer to get my supply voltage up from 208VAC 3-phase to 230VAC. I really wish I had done that so my starting and running amps wouldn't be so high.
That being said, when I did get it hooked up and running for the first time, I had zero issues with contactors welding shut (even when it had a cheap 30 Amp 3-pole definite purpose contactor) because the unloader was working properly (or at least that is what I thought until reading your latest post) and when the pressure switch activated the motor, everything was unloaded and it didn't start making air about 3-4 seconds after startup. When the pressure switch turned off the motor, it would activate the unloader almost instantly, so the motor would actually spin down freely and would take about 20 seconds for the motor to stop spinning. Evidently, that is not what the unloader is supposed to do, so it must have been showing me signs of failure all those years ago.
At the time of the initial install, none of my router jigs or machines were designed to use air pressure to clear out the saw dust chips (in my case PVC chips) so it never really got much use besides turning on once a day or so to refill the tank from leakage. The compressor remained sidelined like this for a good year before I jumped back into it and starting building new jigs that relied on the air pressure. Of course at that time the unloader started to act up (my first cheap contactor welded shut) and I just figured it was due to the cheap contactor. So I bought a larger one at 50 Amps, and it started working again for a few weeks before the unloader failed again and welded shut.
I then started researching it, and started talking to you guys about rebuilding the unloaders and intake valves and draining the old milky oil, refilling, running, draining, refilling, and running with new oil. That part of the compressor is good to go (in my book at least). After that work the unloader was still working but it was touchy. It made it through life about 6 months of hard work before I got to my current situation.
I am going to fix the unloader when the parts come in, but for the time being I REALLY need this thing to limp by until then. My cheapo contactors arrived yesterday and i was thinking I could wire THREE 3-Pole 40 Amp Inductive Contactors in parallel so that each #6 supply line can be split into three parallel paths through each contactor. I am hoping that if one of the
passages get overloaded and heats up (should increase the resistance) and more of the current should then flow through the other two passages to keep it from welding itself together.
Here is a schematic of what I was thinking for this idea...
www.quincycompressor.com
