Dry testing - losing pressure

[Monsoon]

I pressurized the new cold water pipework up to 3bar left it for a couple of hours and noticed it had dropped by 0.5bar.

Im thinking my new hep2o pipework is fine but maybe Im leaking thru the toilet cistern/thermostatic shower/mains non return valve.

Should I be concerned?

Boiler (not connected) = combi

 

[corgiman]

yes you should

as when you introduce water you are going to get wet

find the leak

 

[doitall]

I would test it again properly and safely with water.

3 bar air pressure is stupid beyond belief, perhaps you should visit the HSE sight and do a risk assessment.

And anyway over a couple of hours 0.5 bar would be lost due to temperature cooling

 

[corgiman]

why is 3 bar stupid

Should we not be tesing three times above the expected workingpressure DIA? or have i got me water regs wrong??

 

[doitall]

why is 3 bar stupid

Should we not be tesing three times above the expected workingpressure DIA? or have i got me water regs wrong??

I wrote a little piece about this for our office, and as a result all air testing was banned.

According to the HSE and the Copper Development Board compressed air has 200 times more energy than water.

3bar air equals 600 bar water

 

[corgiman]

blimey I did not know that

:0

 

[doitall]

Just think a high power air rifle is about 20psi.

 

[corgiman]

true

 

[doitall]

Anyway if you dig deeper you will find it is the law when pressure testing with air, to post no entry signs and clear the work area of all but essential personnel.

better add on, gas pressures are ok.

 

[ChrisR]

Pipework at 3 bar won't drop by half a bar due to cooling, unless you got it very hot. The drop from the initial copmpression heating isn't that much.

According to the HSE and the Copper Development Board compressed air has 200 times more energy than water.

Just the sort of pseudo-correct rubbish that can only be answered "...AND...???..."
It depends what you DO with it. My van tyres are at 3 bar. Is it dangerous? Would I be safer if they were full of water? Of course not.
Certainly if an end cap shoots off it goes at quite a speed - I've measured it. So either don't use them while testing, or don't stand over them.

 

[doitall]

Cannot give you figures without looking up the HSE site but quite a few people have been killed by exploding tyres, but of course you are right, anything is ok untill it goes wrong, I was pointing out the fact that it is dangerous.

 

[Onetap]

I pressurized the new cold water pipework up to 3bar left it for a couple of hours and noticed it had dropped by 0.5bar.

Plastic pipework stretches under pressure. There's a section on the Hepworth's website giving recommended test procedures.

And pressure testing plumbing with air is absolutely verboten. Spilt water cleans up so much easier than blood.

 

[Monsoon]

Just pulling together the elements of this thread.

why is 3 bar stupid

Should we not be tesing three times above the expected workingpressure DIA? or have i got me water regs wrong??

I wrote a little piece about this for our office, and as a result all air testing was banned.

According to the HSE and the Copper Development Board compressed air has 200 times more energy than water.

3bar air equals 600 bar water

My thermostatic shower is rated at a max 5bar, so that's 5bar water pressure? and my 3bar air test is pushing it well beyond it's capabilities?

Couple of questions:

If a dry air test is so 'stupid' how comes these test kits are sold through the likes of screwfix with no disclaimers, warnings or in fact any instructions!? This is similar to the tester I used
http://www.trades-direct.co.uk/modules/shop/products.asp?catid=12

The tester I used goes upto 4 bar ... 1 bar higher than I tested my installation. What possible use would someone have for testing a plumbing system at this level if the 4 bar = 800 bar water ?

Finally, the Hep2o site shows a fella pumping up a system to the recommended 18bar. It does say the system is filled with water prior to being pressurized but doesnt the pressure applied to the test come from air pumped in?
http://www.hep2o.co.uk/v2Otesting1.htm
EDIT: Thought about this Hep test some more ... does his pump tester (as pictured) compress the water rather than add air to the pipe work?

 

[Onetap]

If a dry air test is so 'stupid' how comes these test kits are sold through the likes of screwfix with no disclaimers, warnings or in fact any instructions!? This is similar to the tester I used
http://www.trades-direct.co.uk/modules/shop/products.asp?catid=12

Answered here;

http://www.screwfix.com/talk/thread.jspa?threadID=31460&start=0&tstart=0

I think it's daft, too, like selling grenades to school kids. They've probably got disclaimers on the packing.

One aim of the test is to cause it to fail if there are any weak components or joints. The shower might have been pressure tested and it might not. The pipework is new and it hasn't been tested.

Air is compressible, water isn't.

If you pressurize a system with air, the air compresses so you'd be pumping away for a long time with a manual pump to get it up to pressure. The system will contain some 6 to 10 times it's own volume of air at room temperature and pressure. That's a lot of effort. If it fails, all that stored energy is released suddenly. It is an explosion. Bits of metal get chucked around at lethal speeds.

If you pump up a system with water, it will reach the test pressure with a few strokes of the pump, if you've got all the air out. There is very little stored energy.

Steam boilers, pressure vessels, heating coils, radiators, etc., are always pressure tested with water.

 

[doitall]

Back to the leak.

At 3bar you would have heard a leak in the form of a high pitch whistle, another small and unimportant fact, is, after a couple of hours if you had a leak the pressure would have dropped to zero.

Although Chris did say it couldn't be temperature drop, he failed to give an alternative explanation