Why pressure gauge drop without leak

[sanju pradeep]

I have done pressure test for 2" high pressure pipe line by closing the pipe with rubber plugs at the ends. It was 3 bar and I kept it for 24 hours. Its shows a pressure drop of 0.5 bar. The pipe line is fully exposed and I couldn't find any leak on them. What might be the problem. If somebody know, pls share

 

[ShaunCorbs]

Did the temp change a lot ?

 

[sanju pradeep]

Did the temp change a lot ?

yes.. the temperature has changed from morning to night around 5ged C . But I'm rechecking the gauge almost the same time and temperature as the previous day

 

[oz-plumber]

What pipe are you testing, PVC, Copper, Pex.
What are you testing the pipe with, Air, water?

 

[sanju pradeep]

What pipe are you testing, PVC, Copper, Pex.
What are you testing the pipe with, Air, water?

Pvc high pressure class E pipe with water

 

[Chuck]

I don't like the sound of 'rubber bungs'. Are you following a proper methods statement from the pipeline manufacturer? What precautions did you take to avoid air entrapment? What stabilisation period did you allow?

 

[oz-plumber]

Pvc high pressure class E pipe with water

PVC pipe will expand when under pressure, like PEx Piping & composite pipe.
It probably the expansion of the pipe under pressure that is causing the pressure drop.
- Same amount of water filling a larger volume of pipe.

Manufactures of pvc, pex pipe state that you should pump up the pipework 3 times and then do a pressure test.
Pump up once, let it stabilize, pump up again, let it stabilize, pump up third time and there should be no pressure drop.
You don't drain the system after each test, just keep pumping more water into the pipework