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Author Topic: Dry pressure testing, how many bar?  (Read 4355 times)
clivejo
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« on: December 17, 2010, 09:17:08 PM »

I have spent two weeks digging up floors and installing 11 new radiators and copper pipe work.  I have rigged up a pressure meter, attached a radiator bleed plug to my compressor and also capped the flow and return pipes to create a seal.  I intend to pressurise the system, but how many bars should I pressurise up to?

I want to be sure, to be sure, (double sure for the non-Irish) there are no leaks before I insulate the pipes and fill the tracks.  The compressor will manage about 5 bar at a push.

Can I have any thoughts, ideas or suggestions please?

*NOTE*
Its a vented central heating system.
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chickensoup
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« Reply #1 on: December 17, 2010, 09:27:56 PM »

Evening,
            I test my pipework( heating / domestics/gas) on new builds @ 4 bar for 24 hours. Fill very very slowly at a low PSI until pressure achieved. Great thing is when using air, is that you can check all joints with bubbles. Have a valve downstream from installation pipework to isolate pumping source, but also remember to include a pressure gauge on pipework side.

          chicken
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My first recollection of tinkering was wiring a 240v radio cord to a 9v motor to my technic Lego truck, it ended with setting the kitchen on fire!............................I couldn't sit down for two days!
Pat_
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« Reply #2 on: December 17, 2010, 10:24:55 PM »

Oh, well. I say it for the last time on this site, to satisfy my own conscience. Pressure testing with air is very dangerous; because air is compressible a lot of energy is involved. People have have been penetrated by loose fittings. Wet testing is, on the other hand quite safe. At least be aware of the potential danger and don't let anyone stand in line with the pipes.
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clivejo
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« Reply #3 on: December 17, 2010, 10:49:57 PM »

I understand this Pat and as a result have turned off all the radiators, bar the one I'm filling into, as not to create one huge pressure vessel. Its the pipe-work I'm testing, not the rads.

I welcome any ideas to make this safer, I have confidence in my soldering skills, but just want that extra check before I fill the tracks and lay new floors!
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EccentricAnomaly
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« Reply #4 on: December 18, 2010, 09:43:57 AM »

Random thought - would filling most of the system with water first to further reduce the air volume be safer?
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johnrae
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« Reply #5 on: December 18, 2010, 10:04:25 AM »

It's difficult to dry test a plumbing system other than doing it with a gas (air)

The practice of avoiding pressure testing with air really stems from the danger when applied to steel pressure vessels, which are large single volumes.  If these rupture the release of energy is extremely localised and usually involves shrapnel.    Testing small bore copper pipework is no less liable to failure but because copper has the ability to stretch prior to failure and then form a split rather than sudden catastrophic failure, it is somewhat "safer".  It is for this reason that most model locomotive clubs insist on copper boilers.

The main danger with plumbing systems is with olives suddenly giving way because they haven't been tightened sufficiently and the piping whipping about like a demented snake.

So as a rule, pressure test your plumbing by all means but do it alone.   Have no one, especially sweethearts and children in the building when testing other than they acting as your casualty back-up.

As to pressure, 1 bar equates to 10 metres head of water and air will leak out of a joint that water won't, so calculate your total system head, add 50%, divide by 10 and that's a suitable test pressure in metres.  For example, if your header tank is 20 metres above ground, 20+50% = 30,  divided by 10 = 3bar

Any pressure testing I've done, I used a bicycle pump to do the pressurising.  It is much slower than a compressor and lets you know very soon whether there are any obvious leaks as you never get up to pressure.

jack
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johnrae
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« Reply #6 on: December 18, 2010, 10:07:58 AM »

Also bear in mind that if you pressure test with air the moisture in the air may freeze at the bleed-off point when you come to depressurise it and can form a strong enough ice plug to retain pressure.
jack
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chickensoup
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« Reply #7 on: December 18, 2010, 05:32:15 PM »

Oh, well. I say it for the last time on this site, to satisfy my own conscience. Pressure testing with air is very dangerous; because air is compressible a lot of energy is involved. People have have been penetrated by loose fittings. Wet testing is, on the other hand quite safe. At least be aware of the potential danger and don't let anyone stand in line with the pipes.


Pat,
      Is the use of compressed air/gas illegal? as I've spent quite a few years on commercial work, where compressed air was used to check stages of progress on pipework. I too use compressed air using a Rothenberger pressure testing gauge(on domestic pipework), not the wet type but the one with the schraeder type valve. The thing is using water , would mean draining down in the eventuality of leak, and make remedial work very difficult.

 chicken
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My first recollection of tinkering was wiring a 240v radio cord to a 9v motor to my technic Lego truck, it ended with setting the kitchen on fire!............................I couldn't sit down for two days!
desperate
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« Reply #8 on: December 18, 2010, 05:45:13 PM »

And if you are testing gas pipery, you dont want to be filling that up with water.

Desp
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DonL
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« Reply #9 on: December 18, 2010, 05:47:49 PM »

I'm aware of a serious near miss incident when pneumatic testing a relatively small volume - tubular about 150mm dia and about 1.5m long. The rule I've followed in the past is to test wet systems hydraulically and dry systems (gas) pneumatically because the components in the gas systems don't like getting wet  Wink. - as Desparate says.

HSE issue a guidance note which is free to download http://www.hse.gov.uk/pubns/priced/gs4.pdf

Don
« Last Edit: December 18, 2010, 05:50:23 PM by DonL » Logged

Schuco solar hot water - 3300kWh/annum, 16 BP 4175N PV panels - 2.8kWp, log burner and back boiler and 18 Ying Li 235 PV panels - 4.2kWp, 42kW ground mount PV, 9kW Panasonic ASHP
Pat_
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« Reply #10 on: December 18, 2010, 06:12:23 PM »

I'm a novice who, three years ago, was about to be clever and ignore the UFH installation instructions and instead use air to pressure test the system. I checked on the web and found a lot of warnings against doing it, some quite scary.

I can see the arguments on both sides, and at the end  of the day, the HSE document seems to summarise the situation well. The important thing is to understand the risk, and then decide accordingly.

As it happens I have a similar decision this weekend. As I spent the money 3 years ago on the wet Rothenberger tester, that will probably be my choice. If my soldered joints fail under test - then I will have problem. I'm hoping they don't.
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desperate
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« Reply #11 on: December 18, 2010, 06:20:44 PM »

I'm aware of a serious near miss incident when pneumatic testing a relatively small volume - tubular about 150mm dia and about 1.5m long. The rule I've followed in the past is to test wet systems hydraulically and dry systems (gas) pneumatically because the components in the gas systems don't like getting wet  Wink. - as Desparate says.

HSE issue a guidance note which is free to download http://www.hse.gov.uk/pubns/priced/gs4.pdf

Don

Hi Don

Just to be clear, it is not just the components, I was meaning testing the installation pipework before connecting any appliances, but even the pipework itself does NOT want to have any water  in when gas is introduced, the stink they put in the gas is Ethyl Mercaptan plus other nastiness, which will slightly react with water and rot out the pipery double quick.

Desp
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dtl
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« Reply #12 on: December 18, 2010, 08:35:51 PM »

It is important to differentiate between Strength Testing and Leak Testing.

Generally Strength Testing should be performed with water.
Strength Testing is usually the initial test of individual system components after their fabrication. This is generally perfomed at the fabricators facilities. Strength testing is dangerous to perform with air because the system components are untested and any failure can be catastrophic if using air, due to the stored energy of the compressed air.

Generally Leak testing can be performed with air.
Leak testing is generally perfomed after a complete system has been fabricated from individual items. These individual items should have previously undergone separate hydrotests. The object of a leak test is to find any leaks in the connections between the individual items in the system. Generally an air leak is unlikely to result in catastrophic failure.

Before I pressurised a system with air I would need to convice myself that the individual items had been Strength Tested, or the pressure ratings of the individual items could be documented by a recognised QA system.

Before leaktesting a domestic central heating system with air it is important to risk assess the consequences should any of the pushfit, compression or soldered connections fail, due to incorrect make up.
« Last Edit: December 18, 2010, 10:03:23 PM by dtl » Logged
clivejo
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« Reply #13 on: December 19, 2010, 01:18:16 AM »

I am leak testing.  I slowly increased the pressure to 3 bars and leaving it over night.  There was one joint that started to hiss at about 1 bar, but it was a compression joint and easily fixed with an extra turn.  The pressure has held steady since, so I'm happy!  genuflect  Hopefully be the same in the morning. 

Does atmospheric pressure affect the reading at all?
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dtl
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« Reply #14 on: December 19, 2010, 09:17:54 AM »

Does atmsopheric pressure effect the reading;

Yes but only slightly and nothing you need to worry about.

Atmospheric pressure is in the region of approx. 1000 mbar, variations in atmospheric pressure are a fraction of this total pressure.

If there is an decrease in atmospheric pressure then the differential test pressure on your system increases by whatever the atmospherc pressure decreased by.
Visa Versa for an increase in atmosheric pressure.

If your pressure gauge measures in barg then in theory any change in atmospheric pressure will be visible on your test gauge.  Since a barg pressure gauge measures pressure relative to local ambient/atmospheric pressure.
However, it is unlikely that most barg pressure gauges have significant resolution/accuracy to be able to see any change in atmospheric pressure during the duration of your test.

If your pressure gauge measures in bara then any changes in atmospheric pressure would not be visible on the test gauge. Since a bara gauge measures pressure relative to an absolute vacuum.

A variation in temperature during the test period will also effect the test pressure, but in your situation nothing to worry about.
« Last Edit: December 19, 2010, 09:30:16 AM by dtl » Logged
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