Old Curtis C50 Air Compressor

Oilburnr

New member
I bought this air compressor at an auction, don't know much about it except it was used up until the shop closed down a few years ago. Air compressors are somewhat foreign to me, as I've always just had cheapo direct drive oil free units. It's a Curtis Toledo, pics are attached, but serial number on the ID tag says C50U 43L83009

I know quite often these old units will last for decades, but I know no history on it and would like to make sure it's in good shape and stays that way. I've been afraid to take it apart because I haven't been able to find any manuals or quite frankly any information at all on this particular compressor. Oil is full and clean, air filter needs replacement, it turns over nice and smooth, and that's as far as I've gotten. Tank had a couple gallons of water in it when I got it, drained out almost completely clear, little bit of oil
 

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Andrew Mackey

Moderator
Re: Old Curtis C50 air compressor

Disconnect the outlet piping and plug the compressor outlet side with a reducer and 200 pound guage. Turn the compressor by hand and note resistance to turning. As each piston comes up, resistance should be about equal. Continue turning until it gets hard to turn or you get to around 150 PSI. Turn the crank and feel each side against pressure. if one side turns easier, possible worn rings or cylinder. If the guage pressure falls off, again rings or possibly outlet reeds or check valves. if you hear air escaping out the intake, bad inlet checks. If pressure holds, all is good, and one other thing to check. Turn the crank so that the pistons are about 1/2 way up and down, then rock the crank. Any clanking, or if the crank turns a bit before rod contact is taken up, and you will have to do teardown. if all is quiet, you probably have a nice compressor.

water in the reservoir is from condensation. The tank should be drained daily! You will get a little oil, but not too much - nature of the beast. if you are using for tools, just a filter and water seperater should be good. if for painting, a filter and dryer should be used.

If used indoors, I would use an SAE 30 compressor oil. NOT Automotive! Compressor oil is formulated differently. There should be either a sight level or a fill level that will tell you how much oil you need. The fill plug may have a dipstick too. DO NOT overfill! A good equipment shop that sells aod or maintains compressors should have the oil for it. NAPA auto may have it also.
 

G.M.Johnson

Subscriber
Re: Old Curtis C50 air compressor

Not a bad compressor at all. That unit is a dual piston single stage and was made in the 60's. Change the oil out and give it a whirl! If the oil looks fairly clean chances are it is good to go. Curtis compressors of that era are pretty darn tough. Rings and bottom don't wear out as much as the valves do. Over time the springs fatigue and break appart and get lodged between the disc and seat. Good news is you can still get valve parts from some suppliers.
 

Oilburnr

New member
After a year and a half of work consuming most of my free time, I've finally gotten a chance to get back to work in the hobby shop. The motor on this compressor was toast, and I put it on the back burner.

Picked up a harbor freight special 2hp motor for it, changed the oil, and she's pumping great! So nice and quiet too, running around 465rpm.

Only concern I have is that there does not seem to be any unloader on this compressor. Did some compressors not come with them? Is there any way I could add one? Above 90psi the motor definitely struggles to get her goin
 

Vanman

Subscriber
Did you find out what was wrong with the original motor? Often times it is something simple. Old motors are one of my favorite things about old machines. :D While it'll do inna pinch, that china motor will not be nearly as good.

Don't know about the unloaders on this make. If not centrifugal on the back of the pump, then perhaps it's in the pressure switch...

Keith
 

Oilburnr

New member
Pressure switch is just your standard square D unit mounted to the tank. The existing motor was a marathon electric 1-1/5hp and was just tired. Caps were bad, corrosion inside, and the place I brought it to see about fixing it said it was a cheap motor from the 90s and not worth fixing. I ended up rewiring the HF motor to 240v and it seems to do a little better. The 120v wiring is not up to the task. When it kicked on around 90psi the voltage dropped to 87.
 

84prerunner

New member
Back in the day my dad had a similar compressor that had a hard time starting under load (would pop breakers). He added a T in the line between the pump and tank and added a small surge tank. Not even sure what the surge tank was, i just remember a green tank hanging on there. It was probably half the size of a coffee can and made all the difference in letting this thing start. Just something to consider.
 
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