Re: Air pressured testing of pipework

[Ed Sirett]

> I've bought and am using the pressure test gauge from Screwfix > (10179-72). Its been very useful in finding the more obvious leaks > and checking the quality of my soldering (on end-feed fittings). But > even after I've got all the leaks I'm still getting a pressure drop. > What I've been doing is an initial pressurisation to 1 bar to check > with leak detector spray. After fixing any leaks found I've pressured > the system to about 3.4 bar overnight. I'm getting a drop of about > 0.2 bar in about 12 hours and I'm inclined to think that this is from > the push-fit blanking caps I'm using to seal the unfinished pipes. > > Has anyone any experience of air pressure testing central heating > systems? What would be an acceptable (if any) loss? >

In my experience air can get out so much more easily than water that the sort of loss you are measuring should be called a win. In fact that sort of drop in an hour would probably be OK. Not least there will be an initial drop as the pressurized air cools down are it has been put in. It is possible that the rad valve glands are letting a bit by.

[Paul Roman]

Cheers Ed. You've put my mind at ease.

BTW What did you do about the auto bypass requirement on your Keston? (See 'Central heating bypass circuit' thread.)

Thanks

Paul

[Ed Sirett]

Through the bathroom towel warmer - 2 locksheilds on the pipework.

[Andrew Gabriel]

I tested the heating circuits I did this way too. Some got left pressurised for weeks, but didn't lose any pressure. (Mostly, I tested at 2 bar because pumping 3 or so radiators up higher than that with a bicycle pump would kill me. As Ed said, air is much less viscous than water, and will leak out at very many times the speed water would.) What does happen though is the pressure changes slightly as the temperature of the pipework changes. If you want to check for this, make sure the temperature isn't changing, or you leave it until the temperature has got back to same value. Don't forget to check all the radiator blanking plugs and bleeding niples with leak detector too. Also, don't assume there are no leaks inside the Keston -- the drain c*ck was leaking in mine where it screwed into a cast elbow, which showed up as an air pressure drop when I was testing -- fortunately easily fixed.

BTW, you get the same effect doing a soundness test on gas piping if it's changing temperature (e.g. if there a length exposed outside and the sun goes in), only it's much more noticable.

[Ed Sirett]

The testing of gas pipes is done at two magnitudes less pressure. For the reasons you state there is a one minute settling time before the start of the test to reduce the thermal effects.

With an electronic manometer the last digit is 0.00001 bar if you as much as put a hand on a gas pipe the digits will start to move.