Air in gas main

[Comgas25]

Hi guys, running out of ideas for a site I'm currently working on.
In brief, got a 4 year old school with air in the gas main in the science labs. For 4 years the teachers have been purging the gas in the science labs for about 10mins before they can use the bunsun burners.
The next day they have to do the same.
There are x6 labs all with black technigas proving systems. All set and working right. All labs doing the same.
Carried out soundness test on whole site (1.1 m cubed) did not drop at all.
Sized up all gas pipe feeding labs, kitchen and plant room - all correct.
Tested each lab separate and found very small drops. Capped off gas taps (only suitable up to 25mbar ), carried out strength test on Trac pipe feeds in labs - all good.
Repaired all leaks/faults with gas taps.
Every lab now sound.
Still air in labs the next day. (Proving system off through the night).
Any ideas
Thanks in advance

 

[Comgas25]

Gas is turned off then kids play turn taps on no gas comes out but as gas is lighter than air the gas will rise in pipework and taps and fill with air ,when turned on again theres air in pipework? maybe a cause.

I agree mate and also leaks on the pipework made problem worse. I've just never came across this problem before and worked in schools for years. Will see next week when no kids have been messing.

 

[OffshoreGas]

Sounds more like a leak to me, my guess is they shut the gas off when labs are unattended because we all loved lighting gas taps when teachers weren’t about. Your then ending up with pressure loss overnight.
[automerge]1565910561[/automerge]
Surely it should all be capped off until you’ve solved the issue? Pipes full of air/gas are an explosion waiting to happen.