Pressure drops when 650 litre buffer tank is filled with water but no drop with air

[Trevor Rix]

I have a 70kW woodchip biomass boiler installation including a 650 litre buffer tank, all installed in 2014. The buffer tank loses pressure from say 2.58 bars to 0.00 bars within a 48 hour period. Yet there are no visible signs of any water leaks,

When this tank is drained of water then pressurised with air to 2.40 bars the same pressure gauge mounted at the top does not drop. And when all of the joints etc. are treated with soapy water there are no visible leaks.

There was a similar scenario with a leg of 60m of highly insulated underground pipe that lost pressure when filled with water, but did not lose pressure when pressurised with air. When the air was replaced with water there is still no pressure drop.

It is thought that the system has been losing pressure ever since installation. We have yet to refill the whole system with water/inhibitor and turn the boiler back on.

Suggestions as to what may have caused this phenomenon, and any possible long term cures, are welcome.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

For a start you can't pressure test with air anything over 0.5 bar needs to be water

Well, the reason for testing with air was that there were no visible water leaks. So air was tried to see if bubbles appeared in the exposed underground pipework that was covered with water.

The result was unexpected. No more pressure drops!

 

[ShaunCorbs]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Well, the reason for testing with air was that there were no visible water leaks. So air was tried to see if bubbles appeared in the exposed underground pipework that was covered with water.

The result was unexpected. No more pressure drops!

I've had fittings tested on air and no leaks come to water test leak so get your plumber to test the whole system to 10 bar water and leave it for half a day (if you can't 2-3 hours will do)

soon see what's at fault

 

[Last Plumber]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

I am not sure I follow what you are saying. How is that relevant?

If the air you pump into the system is, for example at 21 deg or room temp and you push it into buried pipes, that are say 12deg ( in the ground), the air will contract a lot as the temperature stabilises.

This will give the impression that you're loosing pressure when you're not.

i don't know if they waited when testing with air or give it up straight away.

To me it sounds like that's what happened. You said you had no leak when filled with water !

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

If the air you pump into the system is, for example at 21 deg or room temp and you push it into buried pipes, that are say 12deg ( in the ground), the air will contract a lot as the temperature stabilises.

This will give the impression that you're loosing pressure when you're not.

i don't know if they waited when testing with air or give it up straight away.

To me it sounds like that's what happened. You said you had no leak when filled with water !

Unfortunalely you have not understood what I have written in this thread. Your comments are therefore irrelevant.

There was no pressure drop when air was in the system, nor when the air was replaced with water.

The testing with air took place over several days.

 

[Last Plumber]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Well Trevor,
I have read the thread and commented throughout.
I am only trying to offer suggestions to the ridiculous sounding situation you're in.

It has gone on a while now and I admit I've kind of lost where we're up to.

For the life in me, I don't understand why your installer hasn't solved this by now. It is extremely difficult reading threads and other people's posts, in trying to solve a problem like this
I.e. Not physically dealing with it.

All that said, I understand that you think my comments are 'irrelevant '.

I wish you luck with this. I hope you get to the bottom of it soon.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Well Trevor,
I have read the thread and commented throughout.
I am only trying to offer suggestions to the ridiculous sounding situation you're in.

It has gone on a while now and I admit I've kind of lost where we're up to.

For the life in me, I don't understand why your installer hasn't solved this by now. It is extremely difficult reading threads and other people's posts, in trying to solve a problem like this
I.e. Not physically dealing with it.

All that said, I understand that you think my comments are 'irrelevant '.

I wish you luck with this. I hope you get to the bottom of it soon.

Thanks for taking the trouble to respond. It was only your last comments that I felt were irrelevant.

The installer has not solved the cause of the pressure drops. They are as puzzled as everyone else.

 

[SimonG]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Time to get the manufacturer of the pipe system involved.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Time to get the manufacturer of the pipe system involved.

Uponor were involved a long time ago. They say that their pipe does not leak. But if a leak is found they would investigate. No leak has been found.

 

[SimonG]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Does the system have automatic air vents. Is the underground pipe dead level?

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Does the system have automatic air vents. Is the underground pipe dead level?

Yes there are some automatic air vents, but the red plastic caps are screwed closed.

No, the underground pipe is not dead level.