Domestic fresh water pump diagnosis.

[NealB]

Our fresh water system has been steadily deteriorating.

The pump cycles, but no water flows.

I can suck water through, and the system works until I switch the tap off. Pressure falls quickly and the pump cycles continuously again, but no water flows if a tap is re-opened. It won't prime itself again.

We don't have any obvious water leaks on the outlet side of the system.

If I disconnect the outlet at the pump, and put my thumb over the outlet, pressure builds quickly and the pressure switch turns the pump off. Pressure remains, and if I slightly release my thumb, water sprays everywhere, pressure falls and the pump kicks in again. Squeezing my thumb to stop the flow again, and the pump cuts out.

I interpret this as evidence that the input side of the system is working ok.

However, if I attach a hose from the mains into the outlet side of the system (so mains is providing pressure not the pump), all the tap outlets work fine.

Which makes me think that the 1992 shurflo pump isn't up to the job any more (ie contradicting my first interpretation).

What is strange, to me at least though, is that the flow from the pump seems much greater than the pressure we were putting in from the mains (we only opened the mains hose tap slightly, to avoid blowing all the connections).

Does the esteemed panel have any observations on this, please?

Are there any other tests I can do, or do I just gird my loins, and lash out on a replacement pump and hope that's the problem?

Thanks for any advice.

 

[steve28]

sounds like a valve has failed or the diaphram is no good. pats are available online.

 

[Billjratt]

Check the valves in the pump. It may be that the water pressure you have built up is (over time) lost back to the tank. Or make a "thumb" (short hose, blocked/folded), pressurise, and leave it on until the pump does something on its own - or doesn't...
As to the relative pressures, I think the pump should be set at about 3bar, no idea what you're getting from the main at the end of a pontoon.

 

[DannyB]

Any chance you could spell out what's happening in a bit more detail? I don't see the difference between your thumb over the pump outlet and a closed tap. I'm wondering if you may be sucking air into the pump, when it has been running for some time. If the pump is full of water and you put your thumb over the outlet, you will obviously get pressure, but if you are feeding a tap and the pump has to supply a flow, it may be pulling air in from somewhere and airlocking. I would take a hose from the pump suction to a bucket of water, bleed the air out and then try again.

 

[NealB]

I can't understand the difference between my thumb and a closed tap either!

I'll try your pipe to a bucket suggestion.

Thanks for all suggestions so far. I'm still very open to more!

 

[vyv_cox]

When exactly the same happened to mine, the pump had picked up small blobs of silicone sealant that had dropped into the tank after I replaced its hatch. Two suction valves in the pump had little bits of silicone wedged in them.

Over Xmas the pump in my camper van suffered the same problem, although this time it wasn't me who put the silicone in there.

Suggest you strip the pump and give it a good clean up. It's very therapeutic. Don't use a sharp screwdriver to push the centres of the valves back into their sockets. Use something blunt.

 

[Anonymous]

Most likely you need the new valve kit. It's on a par with servicing a Jabsco toilet in time and complexity.

 

[NealB]

Even I might be able to tackle that one then.

I'll report back in a few days' time....thanks to all.

 

[ytd]

We had same problem and solution as vyv except little bits of sand in the pump. If its the electrical part of the pump at fault you will normally smell burning as soon as you start to dismantle it.

 

[John100156]

As vyv says, sounds like the pump is not pumping as efficiently as it should and needs a clean and/or new valves fitted.

If they all look OK, I suppose it could be a faulty pressure switch which is operating at too low pressure. Enough for thumb but not for system!