Air compressor leak fixed

Compressor with new pipe, comparing to old pipe
Compressor with new pipe, comparing to old pipe

I recently acquired a small air compressor from the Habitat For Humanity ReStore. It is not very fast, but it is very quiet. Anyone who has used an air compressor understands that quiet is nice.

It is pretty old. It was made by DeVilbiss, with an Ingersol-Rand pump head. It doesn’t have a date on it, but the label on it says “Toledo 1, Ohio”, which means it was probably made in the 1950s, or 1960s at the latest (before ZIP codes).

It appears to have had some various changes and improvements over time. There is a pressure regulator and threaded brass pipes that look rather recent.

All in all, it is in pretty good condition, with some minor leakage to repair.

Feed pipe

There was a 3/8-inch copper tube from the pump head to the tank inlet. It was attached with brass compression fittings, which don’t look 50 years old. I don’t like compression fittings on copper pipe because I feel they leak too easily from the slightest cause, and that happened here also. I replaced them with 1/2-inch copper pipe soldered to threaded fittings, with a union joint for disassembly. Flare-nut fittings would have worked nicely also but the diameters were different than the pipe I had.

As part of that, I learned how easy it is to anneal copper. From what I read, the bendable soft copper tubing is just hard copper that has been annealed. And copper is incredibly easy to anneal. Just heat it red hot, and (unlike steel) it doesn’t matter how fast or slow it cools. You can quench it in water and work on it immediately, and my experience was the same. I bent a nice arc using a conduit bender, to align the tank inlet with the pump head outlet. I could have easily used multiple sweat-soldered elbows, which would work well, but I like the look of the curved pipe.

That took care of the leak going into the tank. Unfortunately, there was another small leak which was bleeding the tank empty over night.

Tank leak

I used the tried-and-true method of checking for air leaks, by spraying soapy water on each of the threaded pipe joints. I found a few bubbles and fixed the leaks by resealing the threads with pipe sealing compound (“pipe dope”) and retightening them. However, after I fixed all of the leaks I could find, the tank still bled empty over night.

I was feeling frustrated with not being able to find the leak. In desperation, I submerged most of the compressor in a big tub full of water. I covered the pump inlet with a plastic bag and taped it tight, but kept it above the water. I still didn’t see any bubbles anywhere. That’s when I realized that I wasn’t testing the check valve. I had checked the threads around the valve for leakage (they didn’t leak), but I had not checked the valve operation itself for leak-through. I pulled off the pump-to-valve pipe, and sure enough, plenty of air came bubbling out of the check valve.

I removed the valve from the tank to inspect it. It has holes around the sides on the outlet end, and I could see some specs of something in the holes. I figured some crud blew through the system and perhaps was lodged in the opening, preventing the valve from closing. I opened up the check valve and pulled out the spring-loaded plate. The crud was actually the disintegrated remains of the rubber seal!

I cleaned out the bits of the old seal, and replaced it with a new rubber flat washer. It has now held 100psi pressure for 24 hours. Looks good!

Submitted by amillar on Mon, 2012-02-20 21:02

Leave a Reply

Your email address will not be published.