Finding compressed air leaks

[Kendo]

How do you find leaks in your shop's compressed air system? I thought I had a leak out in the shop piping. But I turned off the valve just after the pressure regulators, and the compressor continues to (slowly) cycle on periodically. I looked online. But the general suggestion is to get an ultrasonic meter for $$. Google app store has an app that uses the phone microphone. But can it really hear ultrasonics? (My wife really hates the noise of the compressor. So this could be a win if I can find the leak...)

[BDA]

Could your regulator be leaking? or could the leak be before the regulator? Get a squirt bottle of soapy water and spray it at every joint and leak possibility. Those joints are normally pipe threads and the "proper" way to seal pipe threads is with Teflon tape or similar. I have found it's easier to use silicone gasket goo. It's not as pretty but I've found it's easier and more reliable. If you have to take it apart, it will be a little more trouble though.

[Kendo]

Just plain old soapy water? It doesn't rust stuff if I can't clean it all? And yes, the regulator could certainly be leaking. I might not have the hearing to catch a small leak.

[BDA]

Spraying a little soapy water isn’t going to rust anything. For that matter, spraying some on the regulator can help show a leak there if there are any.

[Kendo]

Well, I'll try that tonight and see what bubbles up. Thanks.

[dakazman]

 Do you have a drain valve under tank?  I routinely drain the water in tank when pressurized. Blast out all the rust in the lower tank. Then I disconnect the tank from the regulator nightly if tank is full the next day your leak is in your lines .  Hoses leak from small cracks their full length. Disconnect them.
Dakazman

[Kendo]

I just replaced the drain valve. The opening handle had separated from the valve body. But there was just about 1 teaspoon of water in the tank. One advantage of dry California summers.

[EuropaTC]

Another one for soapy water ! 

Believe it or not it was the standard test for shell & tube heat exchangers when I was working. No matter what the material (steel/stainless/nickel alloys/Ti) the workshop would put a low air pressure in the exchanger, typically 5-10lbs with a pressure gauge attached. If the gauge moved overnight the next step would be to go round every weld with soapy water and you'd be surprised at how sensitive the test was. If you've got full compressor pressure then it will be easy to find any leaks.

Brian

[Kendo]

Well, my compressor is getting really clean. But still slowly leaking. I didn't find any bubbles with the soapy water; I think I'll add more soap and try again. In the mean time I noticed my flex hose from the regulator to the hard lines has a label on it 3/4 FIP water heater hose. No spec on its pressure capacity. It is SS braided hose, but still could be a leak source. Since I couldn't do more testing, I wrapped and taped a plastic garbage bag to the whole regulator/hose assembly. I'll see tonight if it's inflated. And there is still the drain valve to test.

[BDA]

If you couldn't find a leak from spraying every possible leak point (hose, fitting connection, drain plug, regulator, etc.) then check the entire length of every tube or hose run. If you still can't find it, it must be a leak somewhere in the tank. If there is a leak in the tank, that could be very dangerous. Your tank could explode!

How old is your compressor? How long have you been experiencing this leak? Have you regularly drained the water from it? Is there any rust or damage to it you can see? What pressure to you keep in your tank?

[Kendo]

It's about 10 years old. Still looks new. I regularly drain it. But summers are dry, so this weekend it just had about a teaspoon of water. I keep it at 150 PSI, to have some headroom for some of my air tools that need 90-100 PSI. It's a 60 gallon two stage compressor. The leak has been since I installed it.  I foolishly put a pipe union in it to be able to separate sections of pipe for later mods. I had always thought that was the leak source. But I currently have a valve shut off before that. Of course, that valve could be leaking 

[dakazman]

  See if your model has a check valve between the cylinder head and tank on the inlet side.
   also ,..  take the cover off the regulator and check the diaphragm seal.
dakazman

[Chuck Nukem]

Sometimes you can find deals on rotary screw compressors at auctions. They are nice and quiet!!

[Kendo]

Well, my new drain valve was leaking. I tried a new kind, that opens with a pull lanyard. Closure is kind of vague. So I don't think it's a good idea for a compressor.

One of these: https://www.mcmaster.com/products/compressor-drain-valves/

I also found a leak in the axle of my hose reel. Are those fixable? The hose reel is past the shutoff valve I used to isolate the problem. So I hope the original leak was the drain valve.

[dakazman]

Glad you found them 
  I can’t answer the reel question I don’t use them.
Dakazman