Todd Rich

15HP, but the 390 is supposed to be paired with a 20HP motor. The Quincy service guy I talked to said that 15HP was fine, but 10HP would be too small. But then again, they said mine was about 25 years old, and the date stamp on the tank is in the 50s.

20 HP, wow.
The trouble is that the motor nameplate on my 390 that I have in my pickup truck, has been completely erased due to unknown reasons (likely reckless cleaning). So I can only be guessing what is the horsepower of that motor. (I will ask our Quincy dealer)
Your compressor is of similar vintage to the one in my garage (mdl 340).
This 390 is Revision 15 made in 1968. 3 years before I was born.

(snip) Yeah. I bought a lot more compressor than I really need, though it is nice to know that I'm not going to run out of air for pretty much anything I can think of doing... With 20HP though, I could kick out 69 CFM @ 175psi.
Good luck. I'd assume at least 15hp though.
Hmm, I guess that means mine is 3 revisions earlier. I know I had a hard time getting the right parts for the unloader. (If I looked at the right pictures, your 390 has an unloader for when it is running at pressure...I think that is a fixed, not variable, pressure setting on it.) Mine was an older version that what was shown in the manual.
Where did you get the info on what revisions were made when?

(snip) Actually, looking again, I think you have a setable pressure for the unloader to kick in. If you don't want to use it, so that when it reaches pressure, the motor shuts off, turn the valve off (the one just above the oil pressure gauge).

That's an insane amount. My sandblaster needs only 15 CFM. So I think that my 340's ability to pump about 24 CFM, works fine for my needs. Although, overnight I started having second thoughts about swapping it for this 390.
Which parts?
I think that a pressure setting is not really the prerogative of the unloader? That it should be an electrical or pneumatic valve that actuates the unloader based on pressure?
I am on very friendly terms with our local Quincy dealer, who knows everything and gets all my orders.

Todd, could you elaborate. I am not familiar with this particular unloader that I have on this compressor. My unloader on the 340 is a lot simpler. I will greatly appreciate.

Ok, here is a picture of mine: The copper tubing coming up from the tank goes to the unloader control pilot. It splits up, with the tubing the comes out on the bottom side going around and connecting up after the control pilot assembly. This line would run straight to the unloader towers if you didn't have the control pilot in place. Here is a picture of mine before I put the contol pilot in place.
Back to the first picture. The on/off valve with the blue handle. When it is closed, the control pilot is bypassed. When it is open, when the pressure reaches your setting, it activates control pilot and vents the air from the line out the left side. The has the unloader towers on top open up. On this one, the pilot assembly is adjustable. You can get ones that have a fixed preset pressure. On the ajustable ones, the tighter you adjust the screw, the higher pressure that is needed for the ball-pilot to kick over and vent.
I did notice that your compressor didn't have any tubing coming up from the tank to this unloader pilot assembly. So, you won't be able to use it until it has air coming from the tank to it.
Let me know if I'm not explaining this well.
Oh, and that little silver colored tab on the left side of the pilot? If you pull it, it forces the pilot to unload the compressor regardless of the pressure.

(snip) Yeah, even with the 15hp motor, this is more compressor than I need, but hey...it is a Quincy, and it is fairly quiet.
(snip) I don't remember the exact ones, but it was mainly the connectors. I figure it was part number drift...we had to go through a couple of part numbers to get active ones. I do remember the 4-way cross pipe part number came as something else. It wasn't a big deal, I just went to the store and go the few that I needed.
Sorry, poor terminology on my part. I think I've answered better following up to your other post. Yes it is a pneumatic valve/pilot that controls the unloader towers that I'm talking about.
Hey, if he is willing to look up the info on 390-12-270987L, I'd really appreciate it. I don't think this one was made in the 70s. Todd

Looks just like mine.
Mine looks like your first picture.
Some not bright people damaged it with forklifts. I will restore it.
Why do you have a ball valve?
Thanks Todd. I saved your explanation.

The other parts, I think answered my questions along with your other post.
He looked up part info on my 1951 model 340 Rev. 3.
Call Mike at Cochrane Compressor. Email me if you want his phone. snipped-for-privacy@algebra.com

The front plate on the lower housing is a bit different.
(snip) OUCH! At least you didn't flip it up on the end of the tank. (Been there, done that.)
(snip)
You mean the valve with the blue handle? Because the control pilot is supposed to have full tank pressure on it, or no pressure on it, and I wanted something that I could activate quickly if needed. Is there a reason I shouldn't have a ball valve there?
I hope it helped.

Well, I called. It was old enough that they didn't have the info in the computer. If I really needed it, they would have to look it up on the factory microfiche. But my serial number range was used in 1957. Given that my tank is date stamped 1956, I think that is a good indicator that I have a 50+ year old compressor.
I've got a rebuild kit for it (gaskets and the like) but given that everything seems to be working well, and as little as I'm using it, I'll just change the oil regularly and keep the kit on hand for an emergency.

I remember. In my case, I cannot take it off my pickup, at all.
No, I was just curious.
Yep. In fact, inspired by your control system, I changed my compressor so that it is able to either run on demand, or run continuously.
i

Yours is newer than mine. Mine was made in 1951.
What is included in your rebuild kit?

(snip) Well, I opened it up, and this was what was inside:

Very nice, where did you get it?

Scales Industrial Technologies, Inc of Pa
It is part number 7079, and it is called the complete overhaul gasket set. I paid $95.87 for it.

Nice. I will try to get a kit for my 340 compressor, although I do not anticipate an overhaul.