Central heating pipe pressure testing

[frank999]

Hi,

I am trying to wet pressure test some central heating pipe work that will be fed from an unvented cylinder.

I understand 10 bar for 10 minutes is a suitable pressure for testing.

At 10 bar the pressure is mostly stable.

I have been experimenting at a higher pressure ie 15 bar, there is pressure loss ... no flexi's, can't see any leaks - so am curious why a slightly higher pressure should have such a different effect.

I have compression isolating valves on the ends of the pipes (4), to vent any air, and some compression fittings before the pump, am I right to think that only a slight weeping out of any of these will cause a noticable drop on the pressure dial.

I have been looking at push fit fittings to make the job quicker and easier, someone suggested a push fit stop end with a bike valve screwed into the end, sceptical that would be water tight though. Pulking olives and weeping fittings isn't ideal.

I also find releasing the pressure and re-pumping a few times helps to reduce the amount of loss ... would this indicate air in the pipes anywhere, I am sure their is none.

Any thoughts appreciated.

 

[Mottie]

Will the central heating pipes be fed from an unvented cylinder? That’s for the hot water, surely? I thought the maximum pressure for either was 3 bar and then the safety valve opens. Why test it to 10 or 15 bar?

 

[Madrab]

When you say central heating pipework that's to be fed from an unvented cylinder? That's a little confusing, you wouldn't normally feed a CH system from an unvented cylinder.

My normal wet testing would be 1 1/2 time the normal working pressure for a min of 60 mins, I usually plan it to be left overnight though.

 

[muggles]

I thought the maximum pressure was 3 bar and then the safety valve opens. Why test it to 10 or 15 bar?

Plastic pipework requires strength testing at 10-15 bar as part of the warranty conditions

 

[Mottie]

Plastic pipework requires strength testing at 10-15 bar as part of the warranty conditions

Oops. I’ve got a few bits of plastic piping in my hot, cold and central heating systems. I’ve never tested them though.

 

[frank999]

Thanks for the replies.

Apologies - should have said Y plan.

My question is - will copper compression fittings deal with a 10-15 bar test, I would have thought so, and ... will a tiny weep from any of these fittings result in a noticable drop on the pressure gauge within minutes ?.

My normal wet testing would be 1 1/2 time the normal working pressure for a min of 60 mins, I usually plan it to be left overnight though.

Can hot water piping from an unvented cylinder can go up to 7 bar ? - so hence 10 bar test.

 

[Madrab]

Can hot water piping from an unvented cylinder can go up to 7 bar ? - so hence 10 bar test.

Under a multiple safety device failure condition then yes it could but to be honest if it's up at 7Bar then you'll have a lot more to worry about that the HW distribution pipework springing a small leak.

If the unvented is working at 3bar nominal then I'd be testing the distribution pipework to 5bar or the set pressure of the lowest PRV whichever is higher. If it's plastic then as suggested, it would be need to be tested at even higher pressures if you ever want to make a warranty claim and could then prove it was all installed and tested as per the MI's.

will a tiny weep from any of these fittings result in a noticeable drop on the pressure gauge within minutes

At that pressure then yep a tiny weep could result in a noticeable drop of say 0.1bar within mins.

 

[endecotp]

will a tiny weep from any of these fittings result in a noticable drop on the pressure gauge within minutes ?.

That depends on how much air is trapped in the system while you’re testing. You should be aiming for zero air but that may be difficult. The more air is left in the system, the less the pressure will drop per drip of water.

As an example: say there in 10 ml of air trapped; you pump it up to 10 bar, and the 10 ml of air is compressed down to 1 ml. Now say 0.1 ml of water leaks; the air will have expanded to 1.1 ml, and the pressure will have dropped to 9 bar.

Temperature changes will also affect the pressure.

 

[frank999]

I flushed out all the pipes out, hopefully all the air was vented out under pressure.

Now say 0.1 ml of water leaks; the air will have expanded to 1.1 ml, and the pressure will have dropped to 9 bar..

Trying to envisage what 10ml of air is ... but think I get it ... thanks.