Pressure relief valve recommendations

reilig

I'm running a gasifying boiler in a pressurised system. Cold pressure is approximately 0.75 bar. Hot pressure goes to a very maximum of 1.5 bar when the boiler and buffer is at full heat. Replaced the PRV about 3 months ago as it was dripping. Over the weekend, I noticed that the pressure has started to drop slightly again so I checked the outflow pipe from the PRV and it has a drip.

I have monitored it carefully over the weekend. PRV is a 3 bar. The pressure gauge is on the same line as teh PRV and right beside it and the gauge never went above 1.3 bar. Even when the system was cold and the gauge pressure down to o.75 bar, there was still a drip.

It has to be a faulty PRV.

I bought the last PRV in a local hardware. It was cheap at around €5.
Can anyone recommend a good make of PRV?

cikearney

reilig wrote: »

I'm running a gasifying boiler in a pressurised system. Cold pressure is approximately 0.75 bar. Hot pressure goes to a very maximum of 1.5 bar when the boiler and buffer is at full heat. Replaced the PRV about 3 months ago as it was dripping. Over the weekend, I noticed that the pressure has started to drop slightly again so I checked the outflow pipe from the PRV and it has a drip.

I haven monitored it carefully over the weekend. PRV is a 3 bar. The pressure gauge is on the same line as teh PRV and right beside it and the gauge never went above 1.3 bar. Even when the system was cold and the gauge pressure down to o.75 bar, there was still a drip.

It has to be a faulty PRV.

I bought the last PRV in a local hardware. It was cheap at around €5.
Can anyone recommend a good make of PRV?

More than likely a boiler problem, contact an RGI

You should have no problem finding a reliable RGI on here

shane0007

cikearney wrote: »

More than likely a boiler problem, contact an RGI

You should have no problem finding a reliable RGI on here

Gasifying boiler is not gas. Generally wood.
Did you check the expansion vessel pressure when system was drained? I would also change the gauge as they can sometimes be faulty also & give you a false reading.

TPM

There are some pretty poor quality PRV/Safety valves out there also. Actually like a lot of cheap parts they are getting a bit too common for my liking.

cikearney

shane0007 wrote: »

Gasifying boiler is not gas. Generally wood.
Did you check the expansion vessel pressure when system was drained? I would also change the gauge as they can sometimes be faulty also & give you a false reading.

My bad, apologies, but prob is still not the prv

reilig

Ok, I'm making some progress on this. I bought another PRV, put it on and topped up the pressure to 0.75 bar on the main pressure gauge. Low and behold, it did the exact same thing. Sickened I was. It can't be the PRV.

So on tuesday night, I went to top up the pressure again. I have an auto filler valve which has a tap fitted on the line above it so that I can turn it off and on. (Not to have it on full time). Its hidden behind the boiler so I hadn't really passed much heed on it before - I just turned it on and watched the main gauge.

Anyway, i decided to pay more attention to the small pressure gauge on the filler valve. I was shocked to see that when the big gauge was at 0.5 bar, the small gauge on the filler valve was at 1.5 bar? Last night I didn't top up the system, left it at 0.5 bar on the big gauge when I lit the boiler and heated the buffer I noticed that the gauge on the filler valve went almost to 3 par - the pressure of my PRV. The big gauge didn't even cross 1 bar.

I'm fairly sure now that the problem is a faulty pressure gauge and I have been over pressurising teh system because of this. I have one ordered from the supplier of the boiler. Fingers crossed.

Thanks for the advice.

shane0007

If the pressure at cold is at 1.5 bar & exceeding 3.0 bar when hot, you have an expansion issue also. Either the expansion vessel is defective, under-pressurised or under-sized.

What is the approx water volume of the system, taking into account the volume of the buffer tank?
What size expansion vessel have you?

reilig

shane0007 wrote: »

If the pressure at cold is at 1.5 bar & exceeding 3.0 bar when hot, you have an expansion issue also. Either the expansion vessel is defective, under-pressurised or under-sized.

What is the approx water volume of the system, taking into account the volume of the buffer tank?
What size expansion vessel have you?

I have a 1500l buffer tank. Boiler holds over 100l and the rest of the system probably holds another 100l. Its normal for the pressure to rise by up to 1.5 bar when its fully heated because of the volume of water. System shouldn't be pressurised to above 0.75 bar. Have a 250l expansion vessel. Its above the size recommended by the manufacturer. Will check the pressure in the vessel.

shane0007

Pressure when cold should be about 1.2 bar. It should not expand that much. Size of expansion vessel is actually over-sized but that is no issue just safer. I would certainly look down the line of faulty expansion vessel or under-pressurised vessel.

reilig

shane0007 wrote: »

Pressure when cold should be about 1.2 bar. It should not expand that much. Size of expansion vessel is actually over-sized but that is no issue just safer. I would certainly look down the line of faulty expansion vessel or under-pressurised vessel.

Thanks for the advice. I'll get the pressure checked. Manufacturer recommends that pressure when cold is 0.5 bar. I'm sure that the fact that it was almost 3 times this is probably the cause of the overflow from the PRV when it heats up.

I haven't topped up the system for the last 2 nights - its showing 0.25 bar on the main pressure gauge on the boiler and 1.4 bar on the small pressure gauge on the filler valve. It drained itself down to this level when it overflowed through the PRV at full heat about 3 nights ago. Its a case of which gauge to believe

I have a new main gauge ordered for it from the supplier so that will tell a tale. But as you suggested, I'll check the pressure in the vessel too.

corkgsxr

Pressure in the expansion could be too high too.

Going by boiler recommendations it should be 0.8-1 bar

But iv noticed when people fit extra expansion vessels they seem to leave it at the pre change of 1.5

shane0007

reilig wrote: »

Thanks for the advice. I'll get the pressure checked. Manufacturer recommends that pressure when cold is 0.5 bar. I'm sure that the fact that it was almost 3 times this is probably the cause of the overflow from the PRV when it heats up.

If the manufacturer recommends a SYSTEM pressure of 0.5 bar then I would always install as per manufacturers instructions, however, are you sure they do not mean a MINIMUM pressure of 0.5 bar? It seems very low as a system pressure from any manufacturer, as most recommend between 1.0 & 1.5 bar. If the expansion vessel is correct & in working condition, the system pressure would never get to the discharge pressure of the PRV.

reilig

A quick note to say thanks for the advice. Last saturday week, I got my plumber in to check the expansion vessel pressure. It was running at well below 0.5 bar. He repressurised it to above 1 bar and we refilled the system which took noticably less time (and water I assume) than usual. Its been working fine for the last week now - probably has dropped by about 0.2 bar, but i suspect that this is only air being removed from the system.

Thanks again for the advice. hopefully I'll have no more problems!!