PRV Valves

[GeoffS]

Can anyone advise how easy a PRV valve is to replace? Is it something that needs a specialist or is it ok for a not too competent, but willing and able to have a go person, to carry out?

[chris w]

Can anyone advise how easy a PRV valve is to replace? Is it something that needs a specialist or is it ok for a not too competent, but willing and able to have a go person, to carry out?

 

If you mean the PRV on top of your calorifier it's a simple DIY plumbing job and the PRVs themselves are readily available. It's the same skills needed as to make any competent plumbing joint.

 

Chris

[rover220]

Can anyone advise how easy a PRV valve is to replace? Is it something that needs a specialist or is it ok for a not too competent, but willing and able to have a go person, to carry out?

 

dont get jobs much easier than this. just make sure the water pump is off before you undo any joints

 

assuming its easy to get at, its a 10 minute job to have a new one fitted.

[LEO]

Hi,

 

It's easy to change a PRV, take time and make a good joint, but why does it need to be changed? - is it leaking or weeping as the pressure in the tank increases due to water expansion? do you have an expansion tank?, also try turning the knob on the PRV to make sure it seats well, as sometimes they get some scale on the seat preventing a good seal.

 

Best of luck, does the water leaking past the PRV leak into the bilge?.

 

Albi.

[GeoffS]

Hello

 

Yes I meant on the Calorifier.

 

It is leaking into the bilge. I have a container to catch as much as I can. It constantly drips. I have turned the knob several times but it hasnt improved it. There is no expansion tank.

 

I did discuss on here once before about how it should work. ie does the pressure build up and then suddenly there is a release (this is what I would expect) or is there a constant flow (if this is the case I would expect it would stop once the water is at a certain temperature).

 

I have re-read my original topic and reminded myself of what was suggested then, so sorry for repeating some of it here!

 

Previous Topic

 

I can easily get 2/3 pints of water collected. The longer I run the engine the more water I get. What I still dont follow, and the reason I was going to change it anyway, is that if it is just supposed to drip, when I turn the knob when the water is hot the valve should be open and presumably wouldnt spurt. But it does.

 

Otherwise there is something I dont understand about how the valves work, which is highly possible!

 

Geoff

[Tony Brooks]

Hello

 

Yes I meant on the Calorifier.

 

It is leaking into the bilge. I have a container to catch as much as I can. It constantly drips. I have turned the knob several times but it hasnt improved it. There is no expansion tank.

 

I did discuss on here once before about how it should work. ie does the pressure build up and then suddenly there is a release (this is what I would expect) or is there a constant flow (if this is the case I would expect it would stop once the water is at a certain temperature).

 

I have re-read my original topic and reminded myself of what was suggested then, so sorry for repeating some of it here!

 

Previous Topic

 

I can easily get 2/3 pints of water collected. The longer I run the engine the more water I get. What I still dont follow, and the reason I was going to change it anyway, is that if it is just supposed to drip, when I turn the knob when the water is hot the valve should be open and presumably wouldnt spurt. But it does.

 

Otherwise there is something I dont understand about how the valves work, which is highly possible!

 

Geoff

 

 

If you turn the valve when the water pump is supplied with electricity (either when it's running or when it has cut out at operating pressure) hot or cold you should get a good spurt. That is normal.

 

Likewise when warming up from cold and at some time after each instance of drawing hot water from the calorifier the valve should give a spurt to some degree as it vents expanding water so the calorifier does not split. All this is as it should be.

 

Each time the valve opens as the water expands the water may trickle down a hose so it might continue to drip for a while after each operation however it should stop when the hose has drained.

 

As long as you are sure the pump cut out pressure is not close to valve opening pressure it certainly sounds like a faulty valve, but you may find you can take it off and strip it to reverse or clean the seal. If the pump cut out pressure is a bit high you may need to adjust it down a bit.

[David Schweizer]

If you turn the valve when the water pump is supplied with electricity (either when it's running or when it has cut out at operating pressure) hot or cold you should get a good spurt. That is normal.

 

Likewise when warming up from cold and at some time after each instance of drawing hot water from the calorifier the valve should give a spurt to some degree as it vents expanding water so the calorifier does not split. All this is as it should be.

 

Each time the valve opens as the water expands the water may trickle down a hose so it might continue to drip for a while after each operation however it should stop when the hose has drained.

 

As long as you are sure the pump cut out pressure is not close to valve opening pressure it certainly sounds like a faulty valve, but you may find you can take it off and strip it to reverse or clean the seal. If the pump cut out pressure is a bit high you may need to adjust it down a bit.

I tried doing that on my PRV, not as easy as it sounds, and the seal was knackered. Quite frankly for what they cost, it is not really worth wasting half a day stripping them down just to find out what you already really knew " they don't last for ever".

[LEO]

Geoff,

 

You might find that renewing it does not stop the dripping as the water heats up and expands.

 

I have plumbed the PRV so it discharges via the side of the boat, to avoid spillage into the bilge. Somewhere on the system there should be an expansion vessel to cope with increases/decreases in pressure as the water expands/contracts, or else the pump cuts in at night, when the engine is switched off and the water cools and contracts.

 

Hope that helps.

 

Albi.

[GeoffS]

I have plumbed the PRV so it discharges via the side of the boat, to avoid spillage into the bilge. Somewhere on the system there should be an expansion vessel to cope with increases/decreases in pressure as the water expands/contracts, or else the pump cuts in at night, when the engine is switched off and the water cools and contracts.

 

Hope that helps.

 

Albi.

 

Hi Albi

Thanks again for your suggestions. I will investigate further but so far I have not come across any sort of expansion tank. I dont know if it affects anything but it is a horizontal calorifier. The pump does not cut in during the night (not since I replaced the leaking one that came with the boat!). The pump itself specifically states that an accumulator tank cannot be used with it. As David says as a PRV does not cost a lot I will try to replace it anyway, but only after checking your suggestions. It seems more sensible to discharge out of the boat but to change that arrangement now is probably not worth it.

Cheers

Geoff

[chris w]

To prevent the water pump's coming on at night, as the water contracts in volume due to cooling, fit a non-return valve (NRV) just before the calorifier in the cold feed.

 

The PRV will always weep as the water is heating if you have no expansion vessel on the calorifier. That's the PRV doing its job as the water expands (otherwise the calorifier would burst). The water inside a typical 60 litre calorifier will expand by about 2 litres as it heats up to say 80 degC. It has to go somewhere and, without an expansion vessel, that somewhere is over the side of your boat.

 

For the avoidance of doubt, the expansion vessel on the calorifier is not the same unit as the expansion vessel (accumulator) on your cold water pump. They are set at different pressures. The cold water accumulator will be a couple of litres in size and be set at around 10 - 15 psi and the calorifier expansion vessel will be about 10 litres in size and be set at around 35psi (a few psi less than the PRV rating). If you do fit an expansion vessel on the calorifier, the PRV should not weep at all (other than in an emergency over-pressure situation!!)

 

Chris

[LEO]

Geoff,

 

Sounds as if you have a Flo-Jet pump, I had one of these, but changed it to a Shurflo which can be used in conjunction with an Accumulator.

 

If it's a horizontal Cylinder you will have to drain a lot lof water out before you can safely remove the PRV.

 

Sure it's not possible to run a Flexy pipe to the bilge drained by a pump to avoid mess due to leakage.

 

Forget incontinence pads for soaking the water up, newspapers do a brilliant job and are cheaper (unless you, or a relative have a problem and the pads are supplied by the NHS).

 

regards.

 

Albi

[GeoffS]

Hi

 

It is a Flojet. I just replaced like for like when I first bought the boat and the existing pump was leaking (one of the surveyor errors!).

 

I dont quite follow about the flexi pipe to the bilge? How do I drain it? What I have now is platic pipe running into the bilge, which I have put a container under, and there is a manual bilge pump.

 

I work for a company that make Inco Pads....!

 

Geoff

[chris w]

Hi

 

It is a Flojet. I just replaced like for like when I first bought the boat and the existing pump was leaking (one of the surveyor errors!).

 

I dont quite follow about the flexi pipe to the bilge? How do I drain it? What I have now is platic pipe running into the bilge, which I have put a container under, and there is a manual bilge pump.

 

I work for a company that make Inco Pads....!

 

Geoff

 

Why not just drill a simple hole in the side of the hull and use a skin fitting to which you attach a length of plastic hose. Then any water would go over the side.

 

I guess, if it's a horizontal calorifier, you may not be able to get the skin fitting high enough above the water. I believe it's 10" minimum to pass BSS IIRC.

 

Chris

[LEO]

Hi,

 

I was wondering if it was possible to extend this pipe so that it discharges into the same area or container that your stern gland drips into, so that water could then be pumped out by the bilge pump? (assuming that you have one). This then saves emptying the container.

 

ATB

 

Albi.

 

I too wondered about drilling a hole, but thought that the calorifer PRV would be below, or on the water line. (as the Previous poster suggested). hence the idea of running a pipe to the proximity of the bilge pump.

Edited October 8, 2008 by LEO

[bottle]

I believe this has been asked before, what is the cut-off pressure for the pump and the release pressure for the PRV.

 

If the cut-off is higher than the release it will always 'leak'.

[chris w]

The PRV will typically be about 3 bar (~42psi). The calorifier expansion vessel (if used) should be set a few psi below this (say 35psi). The water accumulator should be set a few psi below the cut-IN pressure of the water pump. Typical pumps cut-in at around 20psi so the accumulator should be set at around 10 - 15 psi. It's not too critical.

 

Cut-out pressures for typical water pumps are around 30 psi but you are quite correct in that if the pump's cut-out pressure is too high and the PRV too low then the water pump can cause the PRV to drip.

 

Chris

[Nickhlx]

If no expansion tank has been fitted, why does the expanding water not expand back into the cold water tank ? If there is a non- return valve in the way, obviously that would explain it ( remove it ?) Could not another PRV be fitted ( or existing be re-located ?) somewhere where the excess can flow out of the boat via e.g the under-sink waste and/or the original one be blanked off ??

 

Surely the answer is a half-hour job to sort ?

 

Nick

[chris w]

If no expansion tank has been fitted, why does the expanding water not expand back into the cold water tank ?

Nick

 

Water pumps usually only allow water to flow through in one direction (ie: they are their own NRV)

[Nickhlx]

Water pumps usually only allow water to flow through in one direction (ie: they are their own NRV)

 

 

OK - thanks for that Chris - not had ( the need to take) one apart yet but from the noise they make I can "see" the non-return operation at work....

 

Nick

[GeoffS]

The PRV will typically be about 3 bar (~42psi). The calorifier expansion vessel (if used) should be set a few psi below this (say 35psi). The water accumulator should be set a few psi below the cut-IN pressure of the water pump. Typical pumps cut-in at around 20psi so the accumulator should be set at around 10 - 15 psi. It's not too critical.

 

Cut-out pressures for typical water pumps are around 30 psi but you are quite correct in that if the pump's cut-out pressure is too high and the PRV too low then the water pump can cause the PRV to drip.

 

Chris

 

One further question so I can eliminate whether its due to incorrect pressures. I checked the water pump specifications and it cuts in at 15psi and out at 35psi. How do I find the psi that the PRV is set to? Will it be stated on the unit? And are they adjustable? Thanks

[rover220]

One further question so I can eliminate whether its due to incorrect pressures. I checked the water pump specifications and it cuts in at 15psi and out at 35psi. How do I find the psi that the PRV is set to? Will it be stated on the unit? And are they adjustable? Thanks

 

it will say on the unit, usually in "bar". most common are 2.0, 2.5 and 3.0 bar. a standard prv is non adjustable no.

[GeoffS]

Thank you for your help.