PRV blow-off

[Findhorn]

I think that the pump cut out pressure is basically too high for your purposes..35 psi is equivalent to approx. 22 mtrs of head ..way more than you need on a boat ..I would suggest that you reduce the pump cut out to 20 psi and the expansion tank pre charge to 22 psi and hopefully your probs will end

 

[prv]

I don't know all that much about hot water plumbing, I just wanted to say that to keep seeing this thread in the list on the main page is very distracting for me

Pete

 

[JumbleDuck]

I don't know all that much about hot water plumbing, I just wanted to say that to keep seeing this thread in the list on the main page is very distracting for me

Pete

Every time I see it I assume it's about your diet. Or something unmentionable on a family forum.

 

[VicS]

Forget all the pumps and pressures nonsense, your system is set up wrongly.

Not sure what you mean by "set up wrongly". What the OP describes seems to be correct except that the expansion tank is too small for the 30 litre calorifier, but he seems to have figured that out already. This will no doubt cause some blow off from the PRV and it may be necessary to fit a 5 litre CW385 tank in place of the 2 litre CW269

I think that the pump cut out pressure is basically too high for your purposes..35 psi is equivalent to approx. 22 mtrs of head ..way more than you need on a boat ..I would suggest that you reduce the pump cut out to 20 psi and the expansion tank pre charge to 22 psi and hopefully your probs will end

ITYWF that the pump pressure is not intended to be user adjustable. Switching to a lower pressure will therefore probably mean fitting a lower capacity pump.
Other pumps in the range do not, AFAICS, have internal bypasses so that would would then also involve fitting an accumulator tank on the cold water system.


The most important fact in all that the OP has said is, IMO, that he can measure 41 psi, even with a cold system, when the pump should cut out at 35 psi. It is clearly not cutting out at 35psi!

 

[trthebees]

Not sure what you mean by "set up wrongly". What the OP describes seems to be correct except that the expansion tank is too small for the 30 litre calorifier, but he seems to have figured that out already. This will no doubt cause some blow off from the PRV and it may be necessary to fit a 5 litre CW385 tank in place of the 2 litre CW269



ITYWF that the pump pressure is not intended to be user adjustable. Switching to a lower pressure will therefore probably mean fitting a lower capacity pump.
Other pumps in the range do not, AFAICS, have internal bypasses so that would would then also involve fitting an accumulator tank on the cold water system.


The most important fact in all that the OP has said is, IMO, that he can measure 41 psi, even with a cold system, when the pump should cut out at 35 psi. It is clearly not cutting out at 35psi!

I'll agree with VicS and for the sake of 20 pounds or so I'd change the switch. If it's getting a bit sticky, I wouldn't fancy it failing and keeping on building pressure and spraying out of the PRV.
I'll just throw in a suggestion for comment. As VicS says....a larger expansion tank may be beneficial. But where is the exp tank? If it's near a source of heat, the initial nitrogen pressure is going to increase and up the 42 psi (or whatever) setting. Similarly, hot water migrating...particularly if it's above the calorifier pipework-wise, will do the same. IIRC, increasing the temp from say 10C to 50c would increase the pressure by 323/283. I'll stand corrected by others!

 

[pvb]

Only when they are cold water only, hot water has to expand and fitting a heavier PRV will not stop the problem, only blow the system elsewhere!

My new boat has hot water, no expansion tank, and works fine with no leaks.

 

[VicS]

I'll agree with VicS and for the sake of 20 pounds or so I'd change the switch. If it's getting a bit sticky, I wouldn't fancy it failing and keeping on building pressure and spraying out of the PRV.
I'll just throw in a suggestion for comment. As VicS says....a larger expansion tank may be beneficial. But where is the exp tank? If it's near a source of heat, the initial nitrogen pressure is going to increase and up the 42 psi (or whatever) setting. Similarly, hot water migrating...particularly if it's above the calorifier pipework-wise, will do the same. IIRC, increasing the temp from say 10C to 50c would increase the pressure by 323/283. I'll stand corrected by others!

My new boat has hot water, no expansion tank, and works fine with no leaks.

I don't think its about the heat causing the gas filling to expand/increase its pressure. More about absorbing the expansion of the water ( approx 2% in rising 60 degrees) if it is prevented from expanding back to the accumulator tank by an NRV, or if there is no accumulator tank.
Obviously if an expansion tank is located where it will become warmed or if warm water back flow warms it that is an additional complication/factor which has to be allowed for

Some good explanations on the use of accumulator tanks and expansion tanks at
http://www.cleghorn.co.uk/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf.

BTW the OP's pump has an internal bypass which makes an accumulator tank unnecessary. One reason why he probably would be ill advised to change it for a lesser spec'd model!

 

[LittleShip]

I'll admit to only scanning this thread as I thought this had been discussed before but......


The pressure vessel should be charged by dropping the water pressure in the hot water side ( turn off the pump and open a tap) then charge to 1.5 bar. After that turn the pump back on and see if that now cures the problem.

It is also possible that the diaphragm in the pressure vessel is damaged, remove turn upside down and open the shrader valve (sp) if water comes out change the vessel. If clear repressureise and refit.

Tom.

 

[Giblets]

Some good explanations on the use of accumulator tanks and expansion tanks at
http://www.cleghorn.co.uk/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf.

See #11.

 

[BERT T]

I'll admit to only scanning this thread as I thought this had been discussed before but......


The pressure vessel should be charged by dropping the water pressure in the hot water side ( turn off the pump and open a tap) then charge to 1.5 bar. After that turn the pump back on and see if that now cures the problem.

It is also possible that the diaphragm in the pressure vessel is damaged, remove turn upside down and open the shrader valve (sp) if water comes out change the vessel. If clear repressureise and refit.

Tom.

As Tom says check the diaphragm, if it's ok find a spot on the output side of the pump where you can fit a T and screw in a 0 to 4 bar pressure gauge. That is the only way you will find out exactly what the pump pressure is doing.

 

[VicS]

As Tom says check the diaphragm, .................. That is the only way you will find out exactly what the pump pressure is doing.

whatever it's doing it's not cutting out at 35 psi if it's pressurising the tank to over 40 psi, is it ?

 

[BERT T]

whatever it's doing it's not cutting out at 35 psi if it's pressurising the tank to over 40 psi, is it ?

Exactly, that's why I suggested fitting a pressure gauge (not air) to find out.

 

[VicS]

Exactly, that's why I suggested fitting a pressure gauge (not air) to find out.

He measured it with a digital pressure gauge ! Personally I would not have used a digital one but thats because I have three mechanical ones I could have used