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PRV Valve


wullie

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This morning my water pump would not stop running, on checking i found my pressure relief valve on my calorifier was opening and letting the water escape out into canal, i thought it was just a matter of replacing it, changed the unit and was ok for a few times, now it has started doing the same thing once again, its like its getting too much pressure from water pump, not sure if this can happen I've only had lower pressure from pumps not higher, nothing been touched,head scratching.

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The new valve is probably not seating on cylinder properly, I had a similar problem in the summer, if you lift the PRV valve up and down it may after a few good "thwaks" up and down it will clear the scale that may be the culprit , alternatively the PRV valve internal washers/ seal may itself not  be closing. (Which then lets water through it, instead of stopping it).

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Have you measured the pump cut out pressure?

How are the taps behaving? 

If there isn't a lot of headroom between pump pressure and PRV release pressure, something relatively minor, such as a faulty (or absent! :) ) accumulator, or a partially blocked pressure valve on the pump can cause the described symptoms.

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2 minutes ago, Karen Lea Rainey said:

Surely, if all taps are closed off and the PRV  is good the the pump would not be able to run, the water has to escape from somewhere in the system pipework for it to keep running ! Doesn't it, I can't work out any other  fault but the PRV .

 

I cannot work out how it can possibly be the prv, given a new prv does the same. 

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8 hours ago, Karen Lea Rainey said:

Surely, if all taps are closed off and the PRV  is good the the pump would not be able to run, the water has to escape from somewhere in the system pipework for it to keep running ! Doesn't it, I can't work out any other  fault but the PRV .

When you turn off a tap the pump turns off not because there is no flow but because the pressure in your pipes etc rises as the pump runs and no water is flowing - this may only take a fraction of a second if you don’t have any accumulator.  Inside the pump is a little pressure switch and it’s this that stops the pump.  So the pump is continuing to run because in your case the prv is ‘open’ and water is escaping.  This is because the prv is opening before the pressure is high enough to switch off the pump.   Why is not clear, either the pressure switch is blocked or broken so the water pressure is high enough to open the prv or the prv is opening too early.  You need a pressure gauge to know.

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12 minutes ago, Tony Brooks said:

but I think most of us suspect its the pump pressure switch not working proper;y because its a very common fault.

 

I agree, but was explaining why a ng pressure switch could (probably) be the problem.  

 

Added - but without knowing the pressure that the new prv opens at i was reluctant to say that as the op has not confirmed the specification of the new prv that was purchased.  But if a new ‘correct pressure’ prv opens it is almost certain that the system pressure is too high.

Edited by Chewbacka
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37 minutes ago, Chewbacka said:

I agree, but was explaining why a ng pressure switch could (probably) be the problem.  

 

Added - but without knowing the pressure that the new prv opens at i was reluctant to say that as the op has not confirmed the specification of the new prv that was purchased.  But if a new ‘correct pressure’ prv opens it is almost certain that the system pressure is too high.

 

Most PRVs are 3.0 bar. I occasionally encounter 6, 8, 9, and 10 bar PRVs but these are rare.

 

I’ve never seen one less than 3.0 bar and doubt one could be obtained without a lot of research. So I predict the OP replaced his old 3 bar PRV with a new valve of 3 bar or higher, given he seems unable to tell us what he bought. 

 

If im right and the new PRV is 3 bar or higher, and given the old PRV will have been 3 bar, it MUST be a pressure switch failure. 

 

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7 minutes ago, Mike the Boilerman said:

 

Most PRVs are 3.0 bar. I occasionally encounter 6, 8, 9, and 10 bar PRVs but these are rare.

 

I’ve never seen one less than 3.0 bar and doubt one could be obtained without a lot of research. So I predict the OP replaced his old 3 bar PRV with a new valve of 3 bar or higher, given he seems unable to tell us what he bought. 

 

If im right and the new PRV is 3 bar or higher, and given the old PRV will have been 3 bar, it MUST be a pressure switch failure. 

 

Spot on mike, 3.0 bar, i will see about replacing pump, and just get kit for old unit for spare,its a Jabsco PAR MAX SERIES 3 pump thats fitted and will just try and swop for same unit.

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15 minutes ago, wullie said:

Spot on mike, 3.0 bar, i will see about replacing pump, and just get kit for old unit for spare,its a Jabsco PAR MAX SERIES 3 pump thats fitted and will just try and swop for same unit.

A cheaper and more reliable solution would be to buy a Square D pressure switch and use that to replace the built-in one. Pump pressure switches die with monotonous regularity so it’s usual advice to bypass them with a Square D whatever the pump. 

A quick Google found this, you may be able to find one cheaper:

https://www.ebay.co.uk/itm/SQUARE-D-BY-GRIVEN-ITALY-PRESSURE-CONTROL-SWITCH-FOR-WELL-TANK-WATER-PUMP/142796026107?hash=item213f4e70fb:g:Wq0AAOSwHHRa9c0G

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52 minutes ago, Mike the Boilerman said:

 

Most PRVs are 3.0 bar. I occasionally encounter 6, 8, 9, and 10 bar PRVs but these are rare.

 

I’ve never seen one less than 3.0 bar and doubt one could be obtained without a lot of research.

 


A great deal of research not required.

At BES, for example.

Edited to add:

I've also encountered 4 bar ones in boats, such as this Midland Chandlers offering

 

Whilst that might get around a problem of letting by because of "too high pump pressure", I wouldn't recommend it because it sounds too close to what many marine calorifiers are rated and/or tested at.

Edited by alan_fincher
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22 minutes ago, alan_fincher said:

A great deal of research not required.

At BES, for example.

 

Well I never, thanks!

 

Every day is a skool day. In my whole career I've yet to encounter a 2.5bar PRV. I bet they don't sell many! Any idea what appliance it is intended for? 

 

 

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22 minutes ago, Mike the Boilerman said:

 

Well I never, thanks!

 

Every day is a skool day. In my whole career I've yet to encounter a 2.5bar PRV. I bet they don't sell many! Any idea what appliance it is intended for? 

 

 

Dunno!

Fairly certain I have been in a chandery that had 2, 3 & 4 bar PRVs,but I can't remember which.

As an aside or some time the pre-plumbed Surejust/Surecal range of calorifiers have come pre-fitted with 4 bar rather than the 3 bar they used to have., so if you replaced a PRV on one of those, and used 3 bar by default, you could find that whilst it was OKM with a high ump pressure with the old RV, the new one would let by.

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7 hours ago, WotEver said:

Odd how some folk ask for advice and then ignore it...

But read the posts from Wullie and the first respondents. With that level of knowledge and by extension practical ability fitting a new pump may be the betrayer option for them.  Not everyone would be happy or even competent attacking the plumbing and cutting into the electrics. Just to add balance.

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2 minutes ago, Tony Brooks said:

But read the posts from Wullie and the first respondents. With that level of knowledge and by extension practical ability fitting a new pump may be the betrayer option for them.  Not everyone would be happy or even competent attacking the plumbing and cutting into the electrics. Just to add balance.

Point taken but OP is now onto his third pump in as many weeks, all for the sake of fitting a thirty quid valve. Even with labour for someone else to fit it that would have been a cheaper route to take, with savings continuing into the future. 

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6 minutes ago, WotEver said:

Point taken but OP is now onto his third pump in as many weeks, all for the sake of fitting a thirty quid valve. Even with labour for someone else to fit it that would have been a cheaper route to take, with savings continuing into the future. 

 

Where does he say this?

 

As far as I can see, his proposal was one pump swap, and keep the old one for spares.  We don't know hiw old the original was, I think, but resumably it had asted long enough to not be a warranty  claim.  If any pump had only lasted a few weeks, I;d be insisting on my money back.

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