Domestic water pressure

[skip50]

Recently the water pump on the domestic to supply, to galley etc, has changed how it works. The pump operates much more frequently than it used to. There is an accumulator in the system so I thought maybe it had lost pressure. Tried to pump it up but had no idea how much air pressure there should be.

Can anyone give any advice.

Many thanks in advance.

 

[ashtead]

Do you have a leak ? A connection to the calorifier for example is leaking into bilges ?

 

[VicS]

Recently the water pump on the domestic to supply, to galley etc, has changed how it works. The pump operates much more frequently than it used to. There is an accumulator in the system so I thought maybe it had lost pressure. Tried to pump it up but had no idea how much air pressure there should be.

Can anyone give any advice.

Many thanks in advance.

A leak will cause the pump to cut in periodically even while there is no water being consumed. Leaky valves in the pump will cause the same.

There are good descriptions and instructions on sizing and setting up a pressurised water system with an accumulator here : - http://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

 

[johnalison]

According to instructions I have read, the pressure should be 2-3 psi below the cut-in pressure of the pump.

 

[skip50]

Do you have a leak ? A connection to the calorifier for example is leaking into bilges ?

Pretty sure we don't have a leak, the pump doesn't cut in when no water being used. Also the pipes to the calorifier were disconnected recently as we seemed to have a blockage in them affecting the cooling of the engine. The connections off and on the engine were directly connected cutting out the calorifier.

 

[vyv_cox]

If you have pumped the accumulator up too far it is effectively not there, so the pump will operate continuously to feed an open tap. Turn your tap on, monitor the frequency of pump operation as you let air out of the accumulator. Assuming you have over-pressured it the pump frequency will reduce, then increase again as the accumulator pressure reduces past the optimum rate. Then pump it back up to the optimum.

 

[John100156]

Some systems/pumps have a non-return valve in them which if leaking back over time can lead to more frequent pump operation. Also check the pressure relief valve on your hot water cylinder, sometimes ironically more so if well maintained, when lifted they do not re-seat properly as some debris can collect on the seat, but I expect you would notice the overflow if that were the case.

I had a similar problem on my Targa 34 which was only two years old from new - after searching the entire boat I found a minute leak on a t-joint below a basin, I expect you have checked all taps and shower heads etc already for dripping.

 

[vyv_cox]

Some systems/pumps have a non-return valve in them which if leaking back over time can lead to more frequent pump operation. Also check the pressure relief valve on your hot water cylinder, sometimes ironically more so if well maintained, when lifted they do not re-seat properly as some debris can collect on the seat, but I expect you would notice the overflow if that were the case.

I had a similar problem on my Targa 34 which was only two years old from new - after searching the entire boat I found a minute leak on a t-joint below a basin, I expect you have checked all taps and shower heads etc already for dripping.

See post#5. The OP says there are no leaks.

 

[John100156]

Yes but a non-return valve letting-by would not present as a leak.

Likewise a leaking PRV can sometimes be piped out so as not to present as a leak.

 

[VicS]

Yes but a non-return valve letting-by would not present as a leak.

Likewise a leaking PRV can sometimes be piped out so as not to present as a leak.

But if the pump valves let by water leaks back through the pump.

What the Op actually says is that the pump does not cut in when no water is being used. This confirms that they are no external leaks AND that water is not leaking back through the pump

 

[John100156]

I thought the OP said

......,The pump operates much more frequently than it used to.....

If the NRV is letting-by the pump would take water from the CW tank, raise the system pressure, and if no water is drawn-off and there are no leaks, it would cycle off. If the NRV let's by, water pressure would drop as water back flows into the CE tank from where it originated.

 

[VicS]

I thought the OP said, "The pump operates much more frequently than it used to.....

He qualified that by saying that is does not operate when no water is being used! If the pump valves let by and allow the pressure to decay the pump will cut in again at intervals just as it will if there is an external leak.

If it is cutting in and out more frequently than it did previously while water is being used it suggest that the accumulator is not doing its job properly.
The OP seems to realise this which is why he is asking for advice on the correct pressure for it.

 

[John100156]

OK thanks, I was using my iPhone to view but now I'm on my laptop, so I will review again later, read through to see if I can add anything useful.

 

[John100156]

OK So if its the accumulator with a membrane that can deteriorate over time and I would undertake the following checks:

1) First let all air out of the accumulator, or expansion vessel. Only air or nitrogen should be released. If water the membrane could be damaged.

2) If dry, switch pump off and open a tap to release system pressure.

3) Pump up the accumulator/EV with air to say 12 psi just below pump cut-in point which may be say 15 psi.

4) Shut tap and start pump.

5) Check pump cut-out pressure (if you can) and make sure its set a least 7 psi below the operating pressure of any pressure relief valve fitted to your HW cylinder.

Just read the Jabsco info which seems to cover it.

 

[vyv_cox]

OK So if its the accumulator with a membrane that can deteriorate over time and I would undertake the following checks:

1) First let all air out of the accumulator, or expansion vessel. Only air or nitrogen should be released. If water the membrane could be damaged.

2) If dry, switch pump off and open a tap to release system pressure.

3) Pump up the accumulator/EV with air to say 12 psi just below pump cut-in point which may be say 15 psi.

4) Shut tap and start pump.

5) Check pump cut-out pressure (if you can) and make sure its set a least 7 psi below the operating pressure of any pressure relief valve fitted to your HW cylinder.

Just read the Jabsco info which seems to cover it.

That's fine if you have a pressure gauge plumbed in to the line, or a means of doing so. My method needs no gauge, can be carried out in just a few minutes and arrives at exactly the pressure needed for the accumulator to function perfectly. I have used it for well over 20 years, faultlessly.

 

[skip50]

Thank you all for the very useful input and advice. I will give vyv_cox's method a go when I can, and report back.

Thanks again.

 

[John100156]

That's fine if you have a pressure gauge plumbed in to the line, or a means of doing so. My method needs no gauge, can be carried out in just a few minutes and arrives at exactly the pressure needed for the accumulator to function perfectly. I have used it for well over 20 years, faultlessly.

Mmmm not sure I agree, the pump should show its cut-in and cut-out pressure and the prv relief pressure should be known, then all you need is a standard car tyre foot pump which normally has a gauge on it to charge the EV to the correct pressure. I have used this method for well over 40 years....! Still as long as the membrane is in tact all should be well with your method. I design very large commercial systems but the principle is of course the same.

 

[johnalison]

Mmmm not sure I agree, the pump should show its cut-in and cut-out pressure and the prv relief pressure should be known, then all you need is a standard car tyre foot pump which normally has a gauge on it to charge the EV to the correct pressure. I have used this method for well over 40 years....! Still as long as the membrane is in tact all should be well with your method. I design very large commercial systems but the principle is of course the same.

We don't need experts in here.

 

[John100156]

Sad that, I always really appreciate and enjoy Vyv's comments....