Pump intermittently kicking on

[TCL]

Recently my freshwater pump has begun kicking on for about 2 seconds every 5 minutes or so. It did not used to do this.

My system is two tanks, PVC tubing to two individual Sch.40 PVC ball valves so I can select which tank is used at what time, PVC tubing to the pump, an accumulator tank, then downstream to fittings, etc. This pump cycling thing is happening regardless of which tank valve is open.

My question is whether I should start my search for the problem downstream or upstream from the pump. I spent a lot of time for the first few years dealing with air leaks in the system (generally upstream from the pump), but that has been (apparently) all fixed for quite a while now. I can't logically figure out whether the pump would be kicking on to compensate for a loss of pressure upstream (like air leaking in) or downstream (like a problem with the accumulator tank) from itself.

Thanks in advance.
TCL
S/V Tallawah, 1979 Morgan 461

[tkeithlu]

The pressure-actuated switch closes when pressure on the up side of the pump drops,usually at around 35 psi. Somewhere up from the pump you have a very small amount of water leaking out, such that over five minutes the pressure drops below the threshold.

[Dsanduril]

The pump is controlled by a pressure switch on the downstream side, it doesn't know anything about the upstream (suction) side. So, if it is kicking on it means the pressure is dropping on the downstream side = leak. There is a chance that the leak is in the pump's check valves/pump head and is it leaking back into the tank/suction side, in that case you won't find any water anywhere. Easiest way to check that, if so equipped, is to close a valve at the discharge side of the pump/accumulator (isolating the pump from the rest of the downstream plumbing) and see if it still happens. Another small possibility is that the pressure switch is getting tired.

[belizesailor]

Downstream. Most liklely a small fresh water leak or maybe a failing pressure switch.

Where was work last done on the pressure water system? There is your likely leak.

[TCL]

Originally Posted by Dsanduril

The pump is controlled by a pressure switch on the downstream side, it doesn't know anything about the upstream (suction) side. So, if it is kicking on it means the pressure is dropping on the downstream side = leak. There is a chance that the leak is in the pump's check valves/pump head and is it leaking back into the tank/suction side, in that case you won't find any water anywhere. Easiest way to check that, if so equipped, is to close a valve at the discharge side of the pump/accumulator (isolating the pump from the rest of the downstream plumbing) and see if it still happens. Another small possibility is that the pressure switch is getting tired.

Thanks for the response, Dsanduril.

Based on your comment "Easiest way to check that, if so equipped, is to close a valve at the discharge side . . . and see if it still happens," I installed a ball valve after the pump/accumulator, and when I closed that valve, it stopped.

I understand that to mean that there is a leak somewhere downstream, after the newly-installed valve, which I'll need to track down and repair.

Thanks again.

[sailjumanji]

You have a leak either IN the pump, or in the system downstream. Look for a water drip someplace. If you don't find one, then the membrane in the pump might be the culprit. If it gets a little bit of trash or slime in it, its enough to let the pressure bleed back to the suction side. Take it apart, clean the rubber membrane, blow out the slots, etc.

[TCL]

Originally Posted by TCL

I understand that to mean that there is a leak somewhere downstream, after the newly-installed valve, which I'll need to track down and repair.

Which I've now found and will repair in the morning.
Thanks again!