Water pump / pressure release valve / expansion tank

[steviebravo]

After turning off a tap the water pump does not switch off and pumps out water via the overflow pipe into the canal. Consequently I have to switch the water pressure switch on/off when I need to put a tap on.

 

It has suggested that the PRV may be faulty so I have replaced it and has made no difference.

 

Could the water pump or the expansion tank be the problem please?

[Loafer]

Through what overflow pipe, stevie?

[steviebravo]

The one connected to the PRV and calorifier in the engine bay.

[valrene9600]

Through what overflow pipe, stevie?

I would guess PRV

[steviebravo]

That's correct the PRV and calorifier in the engine bay.

[Loafer]

That sounds like a PRV mismatch with your pump. If your water pump pressure is higher than the PRV 'cut-in', then that's what will happen.

 

Has it ALWAYS done this?

[by'eck]

After turning off a tap the water pump does not switch off and pumps out water via the overflow pipe into the canal. Consequently I have to switch the water pressure switch on/off when I need to put a tap on.

 

It has suggested that the PRV may be faulty so I have replaced it and has made no difference.

 

Could the water pump or the expansion tank be the problem please?

 

Water pump maybe but unlikely to be expansion tank. Could be the PRV on your calorifier though.

 

Whatever reason the water pump is either not being limited by its pressure switch, or the pressure it does switch off at is above that which the PRV releases at. The release pressure needs to be well above water pump pressure for the system to work properly, and allow for increased pressure as water heats up. In this latter case the accumulator before, or an expansion vessel (if fitted) after the calorifier should limit this increase.

 

If the water pump never switches off then check its pressure switch and that the contacts to it are not shorting. If it does switch off eventually, again check switch and lower cut off pressure if adjustable, or replace.

 

I wonder if you replaced the old PRV with one of a lower pressure, which would explain the issue. Don't be too tempted to try a higher pressure PRV than original though as it may stress the calorifier. Better to solve the issue at the water pump end if PRV is correct.

[steviebravo]

The new PRV is 3psi as the previous one.

 

I've had the boat a year and it's only just started to happen.

 

The pump has been replaced as it states it was manufactured in 2014. The boat is 10 years old.

 

The pump is a Shurflo Trail King 10 and is 30psi.

[Phil Ambrose]

The new PRV is 3psi as the previous one.

 

I've had the boat a year and it's only just started to happen.

 

The pump has been replaced as it states it was manufactured in 2014. The boat is 10 years old.

 

The pump is a Shurflo Trail King 10 and is 30psi.

Given the above and given my experience with Shurflo pumps I would be guessing the micro switch which cuts the pump out has failed. the switch is in a moulded box at the end of the pump, ignore instructions that indicate no serviceable parts and get to work. The micro switch is operated by a plastic yoke which is activated by contact with the diaphram at the pump end and pivots to open or close the micro switch.

The micro switch can be replaced, have seen them on eBay, the yoke can sometimes fail as well, not had that happen though.

I think I've found suitable micro switches on RS Component website, have also used a buckshee micro switch I had lying around wich I was able to bodge around a bit Good luck

Phil

[steviebravo]

Hi PHIL, thanks for that.

[Iain_S]

If the microswtch is the fault, it's well worth doing Smileypete's relay addition, so that the microswitch only operates the relay, and the relay handles the heavy pump current.

[Tony Brooks]

Also fitting an external pressure switch may be easier.

[Phil Ambrose]

Also fitting an external pressure switch may be easier.

Right again Tony, I've also done this in the past, fitted a in-line switch which worked so well that I left it, still working OK when I sold the boat 4 years after fitting.

Phil

[Tony Brooks]

It seems that nowadays the brick built D Square switches are getting difficult to find and the Whale ones seem to use a micro-switch so I would fit a relay along with a Whale type external switch.

[nicknorman]

You can confirm whether it is the pump not cutting out, or the PRV operating too soon, by putting a car tyre pressure gauge on the accumulator (not the expansion vessel). The air pressure in the accumulator will be the same as the pump pressure and if it wasy above 30psi you will know it is the pump switch. Having replaced the PRV I'd say it is almost certainly the pump switch anyway (presuming you mean 3 bar not 3psi for the PRV pressure )

[steviebravo]

I have used my bike pump to put air into the expansion tank and, up to now, the pump is working as it should, ie it turns off after I've used a tap.

 

I did this last night and my neighbours can't see how this has been the fix. Any ideas?

[Tony Brooks]

Not really but then I have not seen any confirmation of the pump's actual and quoted cut off pressure. If either are close to the PRV opening pressure some form of water hammer (pressure pulses bouncing back down a pipe) opening the valve. Now you have air in the accumulator this would tend to damp the pulses.

[Iain_S]

I have seen something similar in a boat without an accumulator. Not sure whether the pressure switch on the pump was slow to operate, or the "last stroke" of the pump put the system's pressure from below 3 bar to above (gauge fitted to PRV), the PRV would open, about a quarter of a pint of water would squirt out, and the pump would start again, resulting in a pulse of water from the PRV every second or so. Adjusting pump pressure as low as it would go failed to cure it.