leaking air gauges

[Rick Kirchner]

So I just spent an inordinate amount of time machining a new seat face on a specific Craftsman compressor fitting that had somehow become buggered and leaked a ton of air. After putting it all together again and firing it up the only remaining leak was through the tank gauge. there was actually a little puddle of oil inside the face.

Now I've had leaking air gauges before, and others that don't (like the line gauge on this compressor) but what makes one leak and where? Are they repairable in any way? If not, who makes a decent gauge at a reasonable price?

[DaveW]

One reason could be fatigue failure in the "Bourdon tube". That, for instance, could be caused by rapid repeated large air pressure changes in the line from the compressor. Repeated over-pressuring is another possible cause.

Often gauges have a "damper" such as a fine sintered filter in the line or built-in to reduce the probability of fatigue.

[Rick Kirchner]

I've had 'em leak right out of the chute.

[DaveW]

I've had 'em leak right out of the chute.

That could be a result of defective soldering. brazing, or welding leaving porosity between pressurized components.

It's a bit surprising I've never had a leaky gauge, and I've had a lot of them. I've had them mechanically fail so the pointer mechanism no longer worked, but no leakers.

[DanW]

There are two types of mechanical gauges, bourdon tube and diaphragm type. Which ones do you have? Bourdon tube ones seldom leak. Diaphragm ones have a high failure rate.

[Rick Kirchner]

i will have to look

[Rick Kirchner]

I believe its a bourdon tube. Big flat curved tube soldered at the inlet, loose end is attached to the linage going to the needle.

now that I have it out of the case I can pressurize it and see where the leak is - but that anchored end is not only going to see some stress but also considerable vibration.

[DanW]

I believe its a bourdon tube. Big flat curved tube soldered at the inlet, loose end is attached to the linage going to the needle.

now that I have it out of the case I can pressurize it and see where the leak is - but that anchored end is not only going to see some stress but also considerable vibration.

Rick, what's the application? Mechanical vibration or pressure pulsation?

[Rick Kirchner]

that's a good question, because I've owned this compressor since 1984, and probably replaced the gauges 3 times, all because they leak.

It's a 5hp, 240V unit, belt drive, two pistons. Vibrates enough to always scrape the floor below. But I can't see pressure fluctuations in the gauge - probably can't react fast enough.

[J Leonard]

Liquid filled gauge and remote mounted with adequate pressure hose with at least a 90 or 360 loop.

[DanW]

What Mr. Leonard said.

Add, small diameter hose, -3 or -2 to the remote mounted gauge. Noshok and Ashcroft make good liquid filled gauges. There are "snubbers" available that put a diaphram and filled with glycerin between the snubber and the gauge bourdon tube to reduce pressure pulsation but they are expensive and probably overkill.

https://www.mcmaster.com/products/pr...type~glycerin/

[Rick Kirchner]

pretty easy. mounted the gauge in a barb fitting to get it out away from the vise, rotated it such that if the solder re-flowed quickly the tube wouldn't drop out of the block. Took a butane torch and re-flowed the solder, adding some more.

I had to wear some magnifiers to do this, and looking at that magnification it was obvious that the solder had work-hardened and cracked.

Saved myself 20 bucks and learned a bunch to boot. I have another gauge I can fix now.