pressure relief valve help

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cymrocryf

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I have a pressure relief valve on my pressurised water system that constantly keeps going off rather loudly. I guess it may be the pump but I thought to change out the PRV first as thats a lot easier and a lot cheaper. However, it is a 2bar prv and I can only find 3 bar prv in plumbers merchants and its cheap as chips. Do I have to pay for the nose for a specialist 2 bar prv or will I be within normal safty margins by using the readily available 3bar?

Thanks for any advice,

Richard :confused:
 
cymrocryf said:
I have a pressure relief valve on my pressurised water system that constantly keeps going off rather loudly. I guess it may be the pump but I thought to change out the PRV first as thats a lot easier and a lot cheaper. However, it is a 2bar prv and I can only find 3 bar prv in plumbers merchants and its cheap as chips. Do I have to pay for the nose for a specialist 2 bar prv or will I be within normal safty margins by using the readily available 3bar?

Thanks for any advice,

Richard :confused:
Click to expand...

Cleghorn Waring (Jabsco) do a very useful booklet (Water Storage Heaters) explaining pressurised hot water systems and expansion vessels.

www.cleghorn.co.uk

They are also very helpful on the phone or e-mail.

Just a satisfied customer
 
The prv is sized to protect the accumulator. Assuming it was designed by someone who knew what they were doing it would be a mistake to uprate it to 3 bar. However, I don't think there are many water pumps that deliver less than 2 bar, so you may need to reconsider, or at least ask the calorifier manufacturer for advice.

An accumulator may assist in smoothing the pressure peaks but in the end the pressure delivered by the pump will be received at the calorifier. Where the accumulator may be beneficial is if the prv only lifts after the calorifier heats up, in which case the prv is doing its job. Adding an accumulator can absorb the additional pressure due to thermal expansion, up to a point.
 
Thank you all for your thoughts. I do have an accumulator fitted Vyv. I took it for granted that the PRV was at fault as it blows off as soon as the pump is switched on and raises pressure even when cold.
 
The accumulator is also an expansion vessel there to provide some room for water to expand into, the pump pressure switch may isolate the pump at 2Bar but when this water is heated, it expands, if there is no room the pressure increases and prv operates.

The danger may not simply be a damaged expansion vessel, you need to check the calorifier can handle 3Bar too if you fit this device.

Is your hot water getting too hot? Perhaps your thermostats (temp setting and high temp cut out) are not working properly!
 
HI john,

Sorry for the late reply stuck in work. This valve blows when the water is cold as soon as the pump is switched on.
 
Pump pressure switch not operating properly? But likely duff prv.

Could it be some crud on the prv seat, have you rotated top a few times, this sometimes does the trick, I would also check what pressure the pump cuts out if you have the means.

If you have a diaphragm type expansion vessel fitted, relieve the water pressure in the system and check its air charge?
 
Thanks John,

I have taken the prv off and cleaned as best I could and it still blows off as soon as the pressure is raised to normal. The easiest thing I guess would be to buy a 2 bar PRV but I can't locate one despite many internet searches.
Richard
 
Leaking Valve

We had the same problem as you and replaced the valve - purchased directly from Cleghorn Warings website at approx £24.00 - superb service - it arrived two days later, we fitted it and the problem went away - you are meant to rotate the know on the top of the valve three turns monthly but no-one actually tells you that when you buy your boat! Jeanneau don't mention this anywhere in the information provided with the boat (which in my opinion is very poor). Good luck in your quest.
 
Most domestic gas combi boilers have these fitted although they are 3 bar ones and we were warned unofficially by the manufacturers not to touch them as once the seal was broken they often would not seal again.:)

Pete
 
Good man - bound to be a faulty prv. Probably lifting well below 2Bar.

It would be o so easy to diagnose these faults if the boat builder fitted a simple pressure gauge to the water system, cheap as chips nowadays. Cleghorn is likely your best bet.

I know we are supposed to check and clear prv's but I tend to leave the two on my boat alone, they can be a bugger to reseal if any **** gets onto the seat..........
 
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