Curtis B-XXX Compressor With Start Unloader

sbbloom69

New member
HI,
I have a 1921-ish Curtis air compressor. It is very similar to other late teens early 20's small compressor (3" x 3.5" bore/stroke). This compressor, instead of the manual start unloader (finger lever on the intake valve) has an automatic unloader that is operated with a centrifugal lever mechanism. The compressor works, but the outlet valve leaks by. Thus it won't build pressure very fast. I got it from my wife's grandfather who cobbled it together from parts in the 1940's. He said the tank came from a B-17. Has a 1940's Westinghouse induction motor.

I'm going to try and post some pictures of my problem. The outlet plunger valve and it's seat are worn. The plunger is removable under the cap nut and spring on the top of the head. However, the seat in the brass/bronze head is deep in it's hole. I'm sure it needs to be resurfaced. But I'm scared to take too much metal off. What's the best way to cut/grind the valve seat? I can chuck the valve/plunger on my lathe and resurface/cleanup that part. Or should I just try and lap the valve against it's seat to see if I can get it to seal a little better.

The valve I'm talking about is on the right side of the head detail drawing. OR, I could put a simple check valve in the outlet port (its what the outlet valve does anyway). Ideas? Not the prettiest iron, but there's some family history here.

Stu
Los Alamos, NM
 

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sbbloom69

New member
OH, I did find out that the motor is a Delco Type M Thermotron A5865. Nameplate ink is worn away. Looks like only a 1/4 HP. It has a C-1-42 stamped on the plate too. Could that mean 1942? Can't read the ink on what goes to each stamped number.

---------- Post added at 07:23:37 PM ---------- Previous post was at 07:08:55 PM ----------

I have pulled the head. The intake valve seals perfectly. The outlet valve leaks. There is no name plate on the compressor. It does say Curtis St. Louis, cast into the crankcase. The head has AG6D stamped between the head bolts. The Unloader has "Don't Oil the Plunger" and "Pat. Nov. 1921" cast into it.
 

I like oldstuff

Subscriber
The tank is an oxygen tank used on many planes since the late thirties. They were surplussed after the war for around $2. Very well made of stainless and durable.
 

Vanman

Subscriber
When I was a kid I built a compressor using those tanks as well. :D

For a compressor to work effectively and efficiently the volume in the chamber ahead of the outlet valve needs to be as small as possible. So an external valve would not work well.

I would try lapping compound first, then go from there as needed...
 

I like oldstuff

Subscriber
For a compressor to work effectively and efficiently the volume in the chamber ahead of the outlet valve needs to be as small as possible. So an external valve would not work well. I would try lapping compound first, then go from there as needed...
Worst case if you can't get the outlet valve to seal, mount a check valve directly on the outlet.
 

sbbloom69

New member
Yeah I thought about a check valve, but Vanman is right. Too much distance between the piston and the check valve will result in it being much less effective at passing and blocking the output flow. I bought some valve lapping compound on the way home from work. I'll try lapping the valve and seat first. The check valve is cheap too. I may try it anyway, assuming I can find one that will screw right into the compressor output port. I'm just having fun with it. My goal is to eventually make a better base and either restore the Delco motor, or maybe even rig up a mechanical unloader and drive it with my Maytag Twin (still a work in progress).
 
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