Leaking push fit fittings

[riksony]

I have just pressure tested a system of pex pipe and push fit fittings to 6 bar air test. I soon found air escaping slowly from some of the fittings. I changed over to a water test and it shows no leaks, how is this.

 

[ShaunCorbs]

Because an air test is somthing like 4x the pressure (or something like that) of water so you where testing at 24 bar etc

 

[quality]

Pressure is force/area the medium does not affect the applied pressure at static ambient, 6 bar is 6 bar be it beans or gravy.
I cannot explain why you have air leaks but not water leaks

 

[Matt06]

Leak on the air test gauge perhaps ?

 

[TomLane]

Is the pex pipe barrier pipe?

If not then the ingress of air may be possible therefore the expelling of air is also possible.

There is a document somewhere explaining the sciences behind this but I can't find it at the minute!

Some of the more technically minded heating engineers may be able to explain it better than I have done!

 

[AWheating]

air testing is dangerous and should be avoided. Test with water following the manufacturers guidelines normall between 10-18bar for a set period of 15mins to 1hour. some require a test at around 5 bar also.

as for the leaks its prob down to air being compressable and smaller than water.

 

[ShaunCorbs]

Pressure is force/area the medium does not affect the applied pressure at static ambient, 6 bar is 6 bar be it beans or gravy.
I cannot explain why you have air leaks but not water leaks

think you need to read up on your regs mate

 

[Masood]

think you need to read up on your regs mate

I'm with quality on this - 6 bar pressure is 6 bar pressure, irrespective of the medium. Not sure what the regs have to do with it, it's basic physics.

I'm happy to be corrected so please explain (and link to the regs you refer to would be good as well!)

 

[ShaunCorbs]

I'm with quality on this - 6 bar pressure is 6 bar pressure, irrespective of the medium. Not sure what the regs have to do with it, it's basic physics.

I'm happy to be corrected so please explain (and link to the regs you refer to would be good as well!)

[DLMURL]http://copperplumbing.org.uk/sites/default/files/content_attachments/pressure-testing-piping-systems.pdf[/DLMURL]

first para

and its the volume that hurts

well ok your half right you can air test upto 0.50 bar thats it

 

[dancinplumba]

6 bar air test has more energy than 6 bar water test. But they are still 6 bar each

 

[ShaunCorbs]

6 bar air test has more energy than 6 bar water test. But they are still 6 bar each

yea but what happens if the pipework rips apart it wont be 6 bar coming out at the first sec tho will it

 

[lame plumber]

are you sure the joints were leaking or was the compressed air just cooling a bit and hence causing a pressure drop, hence why you have to continually pump for part of an air test!

 

[dancinplumba]

No, because there is more energy in the pressurising with air as said. But 6 bar will always be 6 bar.

 

[ShaunCorbs]

No, because there is more energy in the pressurising with air as said. But 6 bar will always be 6 bar.

not when its sprung a leak tho which is the most dangerous part of an air test, and thats why you can only test upto .5 of a bar

 

[dancinplumba]

Yes I know, but when it's sprung a leak its no longer 6 bar

 

[ShaunCorbs]

Yes I know, but when it's sprung a leak its no longer 6 bar

shouldn't be upto 6 bar in the first place so doesn't matter

 

[lame plumber]

hydraulic testing can be dangerous as well. If your gauge jams at zero and you keep pumping away, when your then see the needle is stuck and you tap the gauge and it wangs upto 12 bar, you think oooh eeer and wonder about letting off the valve a bit to bring it back too 4.5 bar. BUT, and its a big BUT, by the time you have pondered the best thing to do, the JG end cap on the bathroom rad pipe has already failed and is flying across the room towards your lovely wifes' bum. Her resultant scream from the initial pain soon subsides though, as the torrent of water following the recalcitrant cap, soon cools that nasty bruise developing on her backside. Takes longer for her to believe that you never planned this whole episode . Memories of an earlier time in my plumbing life, so great to look back on

 

[ShaunCorbs]

hydraulic testing can be dangerous as well. If your gauge jams at zero and you keep pumping away, when your then see the needle is stuck and you tap the gauge and it wangs upto 12 bar, you think oooh eeer and wonder about letting off the valve a bit to bring it back too 4.5 bar. BUT, and its a big BUT, by the time you have pondered the best thing to do, the JG end cap on the bathroom rad pipe has already failed and is flying across the room towards your lovely wifes' bum. Her resultant scream from the initial pain soon subsides though, as the torrent of water following the recalcitrant cap, soon cools that nasty bruise developing on her backside. Takes longer for her to believe that you never planned this whole episode . Memories of an earlier time in my plumbing life, so great to look back on

sounds like you have experience

 

[Masood]

hydraulic testing can be dangerous as well. If your gauge jams at zero and you keep pumping away, when your then see the needle is stuck and you tap the gauge and it wangs upto 12 bar, you think oooh eeer and wonder about letting off the valve a bit to bring it back too 4.5 bar. BUT, and its a big BUT, by the time you have pondered the best thing to do, the JG end cap on the bathroom rad pipe has already failed and is flying across the room towards your lovely wifes' bum. Her resultant scream from the initial pain soon subsides though, as the torrent of water following the recalcitrant cap, soon cools that nasty bruise developing on her backside. Takes longer for her to believe that you never planned this whole episode . Memories of an earlier time in my plumbing life, so great to look back on

I pictured that as a scene from a "Carry On Plumbing" film, or an episode of Benny Hill...

 

[Masood]

6 bar air test has more energy than 6 bar water test. But they are still 6 bar each

Exactly. Both 6 bar but as air is compressible, it has more latent energy for a given pressure and volume. And will be warmer due to compression which could explain the pressure drop...

 

[kay-jay]

Leaks air but not water because of the difference in density.

Get a bottle of coke and give it a good shake. Leave it.long enough (months) when you open it it will be flat but still contain liquid. The gas has escaped though.

Thisnis why gas pipe isnt plastic.....

 

[goz666]

I once did an air test fella on a fully installed plastic system, I hadn't done the install but was asked to pressure test and confirm whether it was ok. I had an air leak on the system and after isolating various parts of the system and adding cap ends I finally got to the fault and found it was inside a pushfit tee, the installer had started to cut into the pipe and obviously decided to move along a couple of mm, he'd already cut enough way through though to cause a very tiny split which I'm not saying yours is the same, but being inside the fitting just wondering if water would take the easiest route and flow through the fitting.

 

[dancinplumba]

Gas pipe is plastic

 

[Ermintrude]

Different plastics have different pore sizes and thus allow different sized gases through

 

[LPC]

I used to make hydraulic hoses some years back. Once I had a hose I was testing blow at just over 950bar (14k psi). It put a dent in the inch thick steel on the side of the tester and made a noise so loud my ears rang for about 3 days.

Just thought i'd put that out there.

 

[riksony]

thanks for the feed back, I must explain the air was leaking out of the collar of the fittings, when I spayed them with leak detector they bubbled like crazy. I changed over to a water test and the same fittings stayed dry.

 

[Stigster]

I think that as described in the air test procedures, you have gone way over pressure in this medium (plastic pipe/fitting + air). I think that the air molecules are just able to slip by the seals whereas water does not.

 

[riksony]

Thanks Stigster, I feel you could be right, its still holding water test of 4 bar so I think I will leave things alone now.

 

[ShaunCorbs]

Thanks Stigster, I feel you could be right, its still holding water test of 4 bar so I think I will leave things alone now.

8 bar the water test should be

 

[riksony]

With Irish pex the makers ask for 6 bar for 1 hr and 3 bar for 15 mins, working pressure from there on. I did this with water after the air leaks and put it up to 4 bar and it has held since. Do you think I should put up the pressure

 

[ShaunCorbs]

With Irish pex the makers ask for 6 bar for 1 hr and 3 bar for 15 mins, working pressure from there on. I did this with water after the air leaks and put it up to 4 bar and it has held since. Do you think I should put up the pressure

yes 1.5x your incoming pressure

 

[PhoenixServices]

Do exactly as the manufacturer States and take photos. (Not that they prove much) but bum covering is the goal.

 

[zzzjim]

Air test ,very temperature sensitive , and has poor heat removal/equalize ability .
(But leaks easier to clean up - so long as don't get Shot in the bum )

 

[hammers4spanner]

I remember a guy i work with hydraulic tested to 50 bar comp fittings blowing off all over lol .

 

[SJB]

Back in my early days first fixing newbuild totally in plastic (polypipe or osma pushfit) we used to take the rothenberger tester up to 18bar for an hour, if something was gonna go it usually went about 12 and it went good and proper. Used to bring a change of clothes on a Friday with four or five first fixes to test.