Air test pressure drops

[Mixmaker]

Hello guys, i hope you can help. I have pressurize central heating pipes to detect is there any leaks, after i have repaired leaking fitting. but after couple of days pressure has dropped from 3 bars into 2 bars. I could not hear any leaks from fitting i have repaired but how to identify why pressure has dropped? Is there any pressure valve that opening after certain time to release pressure? Or its normal thing when testing with air?

Thank you for advice.

 

[Chuck]

3 bar of compressed air is not safe (too much stored energy and possible shrapnel in the event of failure). It is also not particularly effective at indicating where the leaks are as the sound they generate is usually at ultrasonic frequencies. (FYI. a standard 'gas tightness' test for natural gas pipework uses a gauge pressure of less than 0.03 bar.)

The safe way to test plumbing is to use water pressure possibly with some fluorescent dye and a uv light to localise the problem. It will also give results more quickly because water is much less compressible than air.

Pressure tests should always follow the prescription provided by the manufacturer of the pipe and fittings.

 

[Mixmaker]

The safe way to test plumbing is to use water pressure

Rothenberger pressure test pump, will do the job?

Also what testing pressure suppose to be?

 

[Chuck]

Rothenberger pressure test pump, will do the job?

Yep. I use a manual one. You can probably hire on for the weekend for about £20 if this is a one-off job.

Also what testing pressure suppose to be?

Depends what type of pipework and fittings you are using. For plastic its important to follow the manufacturer's instructions, for both pressure and test durations, carefully.

For generic copper I use 1.5 times the normal working pressure or 3 bar whichever is greater. If a boiler, cylinder, etc. are connected check the manufacturers' instructions. If no change in pressure is detectable one hour after closing the isolation valve you are good to go.

If you have access to British Standards via a library, BS EN 805:2025 is the one that covers this topic.