leaking Calorifier pressure relief valve

[alteredoutlook]

Hi. I have a leaking pressure relief valve in my calorifier. I dont mind them leaking a dribble but a litre a day seems a bit too much to me. The noise of the pump regularly trying to re-pressurise is really getting to me.......

The problem occurs even when the calorifier is cold (i.e. is not warmed by the engine or the electric immersion heater)

My first thought was to remove and clean the PRV. This seemed to 'fix' the problem for a day or so.

Thinking the PRV was just too old i replaced it and again it 'fixed' it for a couple of days.

My current thoughts are:
a) Could it be that the pressure switch in the pump is clogged and needs greater pressure to switch the pump off. The greater pressure is causing the PRV to release. (I just found this in a previous post on this forum!)
b) Or should i simply get a prv with a bigger release pressure. The current prv is 3 bar. (although this seems more than adequate according to other forum posts)

My pump (probably around 20 yrs old) is a Shurflo - 2.8 gpm/10.6 lpm 0.7 bar 10 psi.

My boat is currently in the Baltic and I wont be able to attempt any solution until next summer BUT Any suggestions will be greatly appreciated.

 

[saltwater_gypsy]

If the PRV is dribbling when the tank water is cold then it signifies over-pressure or leakage and on balance it looks like your pump pressure switch is defective. BUT, if that's the case you should be able to observe the system cycling........pump on ...pressure release pops ...pump on ...pressure release pops....and so on.
Mmmmm.. I don't think I've solved this one!!!

 

[vyv_cox]

I think this has been discussed in some detail previously. It would appear that the pump is delivering a higher pressure than the relief valve can cope with. Possible solutions are that the valve may be under-specified, the pump pressure switch may be set too high or defective. A setting of 3 bar on the prv would seem to be more than adequate, pointing to a problem with the pump switch.

Positive displacement pumps, which yours is, have effectively no upper head limit, so if they are not turned off or their suction is throttled their discharge pressure will continue to increase, lifting any reasonable prv. It looks to me like a problem with the pump pressure switch.

On a slightly different tack, I replaced a 20 year old Shurflo pump and was amazed at how much quieter the replacement was. Maybe your pump is giving you a message!

 

[Danny]

My pump (probably around 20 yrs old) is a Shurflo - 2.8 gpm/10.6 lpm 0.7 bar 10 psi.

As vyv_cox and saltwater_gypsy have already said, this looks like it might be a pump pressure switching problem. Here's a possible way of accurately measuring the pump 'cut in' and 'cut out' pressures. Warning: I've never tried this but I can't see why it wouldn't work!

1. Unroll all your FW hose pipe
2. Attach one end securely to a galley tap
3. Hoist other end to the top of the mast. Beware: the hose will get heavy when full of water!
4. Turn on the tap...

Assuming the mast is more than about 25' high the pressure should not be high enough to push water out of the top of the hose.
Now lower the hose until water flows out of the top. Raise it again until the flow stops. The heights from the tap to the end of the hose represents the pressures at which the pump switches on and off. 1 bar is equivalent to about 33' of water so 0.7 bar would be about 23'.

Possible problems I can see with this method are:
A wet cabin.
A lost halliard.
An amused and/or bemused audience.

 

[vyv_cox]

As vyv_cox and saltwater_gypsy have already said, this looks like it might be a pump pressure switching problem. Here's a possible way of accurately measuring the pump 'cut in' and 'cut out' pressures. Warning: I've never tried this but I can't see why it wouldn't work!

1. Unroll all your FW hose pipe
2. Attach one end securely to a galley tap
3. Hoist other end to the top of the mast. Beware: the hose will get heavy when full of water!
4. Turn on the tap...

Assuming the mast is more than about 25' high the pressure should not be high enough to push water out of the top of the hose.
Now lower the hose until water flows out of the top. Raise it again until the flow stops. The heights from the tap to the end of the hose represents the pressures at which the pump switches on and off. 1 bar is equivalent to about 33' of water so 0.7 bar would be about 23'.

Possible problems I can see with this method are:
A wet cabin.
A lost halliard.
An amused and/or bemused audience.

Nice one! I like it.

 

[Wino]

I had same problem a few weeks ago - caused by calcium build up on the pressure/valve seat.
Some valves have a knob on top that should be turnes every week or so, this lifts the valve, turns it slightly and clicks it back.
I replaced mine but was told it is possible to free them by soaking in a mild acid vinegar or hydraulic.
Best of luck
roj m

 

[Ex-SolentBoy]

As vyv_cox and saltwater_gypsy have already said, this looks like it might be a pump pressure switching problem. Here's a possible way of accurately measuring the pump 'cut in' and 'cut out' pressures. Warning: I've never tried this but I can't see why it wouldn't work!

1. Unroll all your FW hose pipe
2. Attach one end securely to a galley tap
3. Hoist other end to the top of the mast. Beware: the hose will get heavy when full of water!
4. Turn on the tap...

Assuming the mast is more than about 25' high the pressure should not be high enough to push water out of the top of the hose.
Now lower the hose until water flows out of the top. Raise it again until the flow stops. The heights from the tap to the end of the hose represents the pressures at which the pump switches on and off. 1 bar is equivalent to about 33' of water so 0.7 bar would be about 23'.

Possible problems I can see with this method are:
A wet cabin.
A lost halliard.
An amused and/or bemused audience.

I was always average at physics. Wouldn't it depend on the diameter of the hose pipe?

 

[Danny]

I was always average at physics. Wouldn't it depend on the diameter of the hose pipe?

No.

 

[BlueChip]

I think this has been discussed in some detail previously. It would appear that the pump is delivering a higher pressure than the relief valve can cope with. Possible solutions are that the valve may be under-specified, the pump pressure switch may be set too high or defective. A setting of 3 bar on the prv would seem to be more than adequate, pointing to a problem with the pump switch.

Positive displacement pumps, which yours is, have effectively no upper head limit, so if they are not turned off or their suction is throttled their discharge pressure will continue to increase, lifting any reasonable prv. It looks to me like a problem with the pump pressure switch.

On a slightly different tack, I replaced a 20 year old Shurflo pump and was amazed at how much quieter the replacement was. Maybe your pump is giving you a message!

I had a pressure switch fail on my pump and the noise the relief valve makes when it blows is quite distinctive and unmistakeable, nothing like a dribble more like a 'whoosh'.
I'd just put my money on dirt on the seat of the valve, as the OP has changed the valve already, if turning the knob on the valve a bit doesnt fix the problem I would guess the new one is faulty. They only cost a few £'s in a plumbers merchants, I'd be tempted to change the valve for a new one.