Slight pressure drop over night

[Inchbyinch]

Hi all, 

Making progress, I've a pic attached of the pour in action.

however after the pour I have a pressure drop in the system we have gone from 2.8 to 2.2 over 24 hours. Do I have a leak?

 

 

[Nickfromwales]

Repressurise and give it another 24hrs. There's a lot of pipes coming out of the slab, what's the method for pressure testing all those, and what are they all ?

[PeterW]

It could well be due to the heat of the concrete curing has increased the pressure and it has now settled down

keep an eye on it over the next 24 hours as it should have stabilised. 

[Inchbyinch]

Thanks Guys, 

I'll up the pressure again later on.

The pipes coming out of the ground are the water distribution pipes. I ran them in insulated 16mm pert-al-pert as well. They are not pressure tested but ran under ground to rise in the walls as they go up, saves chasing after. If there is a problem we will run alternates in the roof space.

we used the mains pressure to test, just shy of 3 Bar. Also have pressure tester that arrived late so could jack it up further if needed.

rgds,

ed

 

[Jeremy Harris]

Bear in mind that, with no air anywhere, there may well be a marked variation in pressure with temperature.  Water volume increases with increasing temperature above 4 deg C.  Because of this the pressure will vary, as it's a closed system with nowhere for the additional volume to go (except the air bubbles that will inevitably be in there somewhere at this stage).  Odd things happen when you dissolve gasses into water as well (which is what will happen with an initial fill like this).  Ideally any pressure test like this needs a near-constant temperature.

There is another effect too, caused by the way concrete contracts slightly as it cures.  This is useful, as it causes it to grip reinforcement very tightly, but a nuisance when you have pipes running through it and are trying to measure pressure, as the pipes will be squeezed as well.  This means you can see a slight pressure rise as the concrete cures and very slightly compresses the pipes.

I'd not take too much heed of any variation in pressure measured between pre-pour and post-pour.  It's likely that there were temperature variations, and the effect of the concrete initial cure, that have messed up the readings.  Best to do the test when conditions are stable.

FWIW I didn't bother with any pressure testing at all.  I took the view that the pipe was pretty tough, there were no joints anywhere and a visual inspection would be fine.  I used the same philosophy as when laying MDPE water pipe, where the chances of the pipe itself developing a leak are so close to zero that it's commonplace to not bother pressure testing it before backfilling trenches.

 

 

[Inchbyinch]

Well after much sweating this morning and wondering how I was going to fix my leak....the pressure was 3.4 Bar this afternoon with no intervention taken. It is quite a balmy afternoon here today so I guess it is all down to temperature.

it was some job trying to get the pipe in between all that re bar in the retaining wall. And the spacing question was answered for me as 200 was as good as it was going to get. 

Thanks for all the advice, super!! 

Ed

[Inchbyinch]

Soon after the pressure was north of 6 Bar so we left it off....no leaks thankfully!! 

[Jeremy Harris]

Just goes to show what a bit of heat does to a fluid that expands yet is (to all intents and purposes) incompressible!

[Onoff]

Mine did EXACTLY what it said on the tin....or was it Nick?

I pressurised it to nom. 3 bar, it rose a bit whilst curing initially then has sat at 3 bar with the "test" water in it for months now.