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Prv letting by.


fudd

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Good morning. I recently fitted a new pump. It is more powerful than the old one. 5 gpm. It’s got an intermittent fault at the pressure switch end but I can get over it temporarily by wedging the connection. The trouble is that the prv keeps letting by and I loose all the hot water. It’s a 3 bar prv. 

The pressure vessel needs to be charged at 45 psi. Is there an issue here or could the prv be uprated. Thanks. 

Steve P. 

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I would think the prv is there to protect the calorifier. You probably could install a bigger prv, but would then risk damaging it. 

 

I reckon either :

 

1.external square d pressure switch

2.pressure reducing valve 

3.lower pressure pump

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Just now, rusty69 said:

I would think the prv is there to protect the calorifier. You probably could install a bigger prv, but would then risk damaging it. 

 

I reckon either :

 

1.external square d pressure switch

2.pressure reducing valve 

3.lower pressure pump

Thank you. I understand that. I’m just wondering if , say a 4.5 bar prv would help. It’s a sure-cal calorifier and I’m not sure of the pressure it could manage safely. 

2 minutes ago, Alan de Enfield said:

Why not take the simple approach and just replace the pump with one of the same spec as the previous one - you know your 'whole system' functions perfectly with that ?

The old pump was near to useless. No flow and low pressure. Thought I’d upgrade. 

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2 minutes ago, fudd said:

Thank you. I understand that. I’m just wondering if , say a 4.5 bar prv would help. It’s a sure-cal calorifier and I’m not sure of the pressure it could manage safely. 

The old pump was near to useless. No flow and low pressure. Thought I’d upgrade. 

Flow and pressure are two different characteristics

You could have a 100 litres a minute at 3 bar, or you could have 10 litres per minute at 5 bar .

 

Maybe parts of your system are 'furred' up reducing the flow ( have you checked your filters in each tap) ?

I think all of my boats have had a 3 to 3.5 bar and 22 litres/min pumps. We have a very 'comfortable & adequate' spray from the shower.

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4 minutes ago, fudd said:

Thank you. I understand that. I’m just wondering if , say a 4.5 bar prv would help. It’s a sure-cal calorifier and I’m not sure of the pressure it could manage safely. 

 

The answer is no it won’t handle the 50% rise in pressure safely. It will burst or split sooner or later. Don’t upgrade it. Absolutely definitely don’t do it. Get the right pump or fit a pressure reducer. 

 

 

 

 

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46 minutes ago, fudd said:

 

The pressure vessel needs to be charged at 45 psi.

 

"""The pressure vessel needs to be charged at 45 psi."""

 

Wrong.   The accumulator vessel should be charged to half the pump pressure.

 

If you up the prv you will be risking wrecking the calorifier.

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21 minutes ago, Boater Sam said:

"""The pressure vessel needs to be charged at 45 psi."""

 

Wrong.   The accumulator vessel should be charged to half the pump pressure.

 

If you up the prv you will be risking wrecking the calorifier.

Here are the instructions. 

45AD2F54-462F-496D-A68E-2F9B0199FF28.jpeg

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9 minutes ago, Boater Sam said:

Don't care, they are wrong. Half pump pressure.

Charged to 47 psi would be for a pump giving 94 psi static pressure, thats 6 bar +, crazy.

I can only go by the instructions. Ill try letting it down. 

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29 minutes ago, fudd said:

I can only go by the instructions. Ill try letting it down. 

hat won't stop the PRV opening until you reduce the pump cut out pressure to maybe 5psi or so below the PRV opening pressure. This allows a bit of "headroom" for pressure pulses when you turn the taps off.

 

The instructions seem to be confusing an accumulator with an expansion vessel. Both can be identical bits of kit but pressurised differently and in different parts of the circuit doing different jobs.

 

An expansion vessel goes on the calorifier side of any one way valve in the supply, normally in the hot take off pipe. This is to prevent a pressure rise as the calorifier heats up and the water expands. it is pressurised to about the pump cut out pressure as the instructions state.

 

An accumulator goes on the pump side of the said non return valve and it provides a store of pressurised water so the pump cycling period is longer when the flow form a tap/shower is less than the pump output volume. This is pressurised to the pump cut in pressure or about half the cut out pressure both of which are more or less the same.

 

So the question is "which do you have, an accumulator or expansion vessel"? But neither will have any effect on the PRV letting by unless you reduce the pump's output pressure.

 

 

 

 

 

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17 minutes ago, Tony Brooks said:

hat won't stop the PRV opening until you reduce the pump cut out pressure to maybe 5psi or so below the PRV opening pressure. This allows a bit of "headroom" for pressure pulses when you turn the taps off.

 

The instructions seem to be confusing an accumulator with an expansion vessel. Both can be identical bits of kit but pressurised differently and in different parts of the circuit doing different jobs.

 

An expansion vessel goes on the calorifier side of any one way valve in the supply, normally in the hot take off pipe. This is to prevent a pressure rise as the calorifier heats up and the water expands. it is pressurised to about the pump cut out pressure as the instructions state.

 

An accumulator goes on the pump side of the said non return valve and it provides a store of pressurised water so the pump cycling period is longer when the flow form a tap/shower is less than the pump output volume. This is pressurised to the pump cut in pressure or about half the cut out pressure both of which are more or less the same.

 

So the question is "which do you have, an accumulator or expansion vessel"? But neither will have any effect on the PRV letting by unless you reduce the pump's output pressure.

 

 

 

 

 

This is it Tony. 

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16 minutes ago, WotEver said:

That looks like an accumulator as best I can see the pipework. So it should be pressurised to around half the pump cutout pressure or lower. 

I am not so sure. I explained to the OP how to tell the difference so he posts a photo giving no clear shots of ALL the pipe work and any valves/fitting associated with it. Tends to pee me off a bit.

 

 

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12 minutes ago, fudd said:

I’ve had to turn it off. 

Turning the pump off and opening a tap will NOT reduce the air pressure in the vessel but will do so in the water system. That gauge is reading water pressure NOT air pressure and I can't see a valve by which the internal air pressure can be adjusted. That is not to say there is not one, just that I can't see one. The set-up looks more like an all in one yacht system to me with the pump mounted on the pressure vessel, probably American, not that that in itself should make any difference to the performance.

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14 minutes ago, Tony Brooks said:

I am not so sure. I explained to the OP how to tell the difference so he posts a photo giving no clear shots of ALL the pipe work and any valves/fitting associated with it. Tends to pee me off a bit.

Looks to me like the water enters from the right, through the filter to the pump, out the other side of the pump to the T piece above the accumulator (with the pressure gauge), then out the other side of that T, down and up the left hand side. 

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33 minutes ago, WotEver said:

Looks to me like the water enters from the right, through the filter to the pump, out the other side of the pump to the T piece above the accumulator (with the pressure gauge), then out the other side of that T, down and up the left hand side. 

Exactly. There is a Schrader valve on the pressure vessel. 

50 minutes ago, Tony Brooks said:

I am not so sure. I explained to the OP how to tell the difference so he posts a photo giving no clear shots of ALL the pipe work and any valves/fitting associated with it. Tends to pee me off a bit.

 

 

Sorry about that Tony 

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21 minutes ago, fudd said:

Exactly. There is a Schrader valve on the pressure vessel. 

Once you have the pump cutout pressure correctly set, pump the accumulator up to half that pressure and you’ll be good to go. 

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