Leak in Air line

Hi, I have about a 3000 sq ft shop, that has a dry sprinkler system that is about 20 years old. The way it works is it is filled with air through 4" down to 1" pipes. Several of the pipes have rusted through and some of the joints have been replaced at considerable cost. It appears to be the worst in the cold attic horizontal runs where water condenses I think.
Anyway it should hold air pressure for 6-8 hours but only goes 45 minutes before the compressor kicks on. I have hunted leaks many many times with a soapy spray bottle, but cant find them. Is there some way that I could suck in a colored air or smoke or something into the compressor and look for the colored leak? That may be stupid or illegal. Does anyone have any ideas of how to isolate those tiny leaks?
thanks,
Stevo

Look up ultrasonic leak detection.

If you can isolate parts of it that would be a good start but it might work to find some leaks by charging the system and at night when everything is silent see if you can hear leaks.

Do both of the above. Check after everyone has knocked off for the day. You will hear the bigger leaks. Hire or buy an ultrasonic leak detector. They work. It is well worth the effort. This method saved a steel mill I was working at the purchase and operation costs of an extra 1200cfm compressor. Cheers

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Originally Posted by Chris Parks

If you can isolate parts of it that would be a good start but it might work to find some leaks by charging the system and at night when everything is silent see if you can hear leaks.

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That's what I did, three valves to isolate different sections in case of a leak.

In my initial testing I found that what I've always used to find leaks, a dishwashing liquid solution, didn't work nearly as well as I hoped for tiny leaks. What really works well is the soap bubble liquid made for kid's bubbles. I bought a gallon for almost nothing at Walmart after the summer season.

Also, consider your configuration. If you are getting condensation in the horizontal lines in the attic you can eliminate almost all of it by adding some condensing lines with traps and/or water separators before the air gets to the attic. I've read recommendations to have at least 25' of line directly out of the compressor, installed sloped to allow any condensation to drip into a trap. There is a recent thread here where someone recommended installing this line in more of a radiator configuration - that would take less space.

Is it practical to slope the attic lines?

I run my air through some line to a vertical trap, through a water separator, then a desiccant drier before it gets to the regulator and manifold and valves for each of three lines.

I've never used an ultrasonic leak detector but I have used a halon leak detector. The line (we were testing pressure vessels) was filled with low pressure halon gas and the ultra-sensitive detector probe moved along the welds and connections. Perhaps you could rent one or hire a testing company.

JKJ

I don't use a brush to apply the soapy liquid just spray it with a hand pump sprayer. Interesting point about the kid's bubble liquid, it definitely is lighter in viscosity.

A Windex spray bottle works too. Bubbles aren't as big as with dish liquid, but they keep foaming up longer, and will signal a tiny leak with tiny bubbles. I keep tire plugging tools in my truck, Windex for glass, and found out from desperation one day. I don't bother to keep soapy water in the truck any more.

Hi Folks,
Thanks for all the suggestions. The system doesnt have valves to isolate parts of the system. In talking with one of the fire technicians he indicated that it might not be legal to install them as they could be left shut. I am going to definitely figure this out, as the thing has to work.
The compressor is only two years old and seems high quality, but sometimes the pressure switch doesnt turn on the compressor and then alarms go off.

I cant slope the horizontal lines as about half is in an attic and all of the areas below are occupied.
I really like the idea of a drier or manifold and also the ultrasonic devices.
I will get this thing solved but it may not be cheap. Luckily I got a buy on the building so that helps some.
Thanks so much for all the help.
Steve

Only thing I can come up with is to rent a tank of CO2 and a regulator and use a CO2 detector to check your joints. You could use freon and have your favorite AC guy check it out but CO2 should be cheaper.

Basically, the idea is to use a commercially detectable gas and pressurize the system to see where the leaks are via a detector.

Don

Best way is the way my Father did it for high vacuum lines. pressurize with He and use He detector. He is so small it will leak out faster then any other gas other then hydrogen, which is not a good gas to use.
Bill D.