freshwater pressure

[Janet Plume]

my freshwater diaphargm pump won't cycle off after accidentally running the tank dry.i've refilled the tank and now have a constantly running pump.i've determined the pump is ok, even replaced the pump and have the same problemi spent most of yesterday unsuccessfully checking the lines for a leak.is a leak in a pressurized line easily discernible?what else could be causing this problem? the water flow is fine, i am just going to burn out the pump.does filling the water tank too full ever cause this problem?could a pocket of air somewhere, say in the heater, cause this?the pump is a shurflo 3.8 gpm. isnt this a self-priming pump?i have a seaward water heater and no accummulator tank.could this be a low voltage problem? it continues even when hooked up to shore power.janet plumevision 32

 

[Don Berger]

air leak

Don't know what filling the tank "too full" means - did you plug the vent and pressurize the tank?Sounds to me like two possibilities:1. an air leak or entrained air in the tank and lines. Try disconnecting the line from the tank to the pump and allowing gravity flow to see if you are getting any air, and2. maybe a restriction in the line preventing the pump from getting water which you can determine from doing #1.I assume you also checked the filter in the line to ensure it isn't clogged???Don

 

[Ed Ryan]

filter check

Sounds like the in line filter that's usually located on the suction side of the pump may have gotten clogged when the tank was pumped down, possibly by pulling in "stuff" that was lurking on the bottom of the water tank. If that filter is clogged, the pump can't build up sufficient pressure to shut off. (One other thing to try is to open up all the faucets with the pump running to make sure there is no air in the system.)

 

[Don Alexander]

Suck It!

Janet,I had to clear a similar problem on a friend's Hunter. They too had run the tank dry and after refilling - no water came through, so no water pressure, so pump ran continuously.I figured the non return valve, either in the pump or upstream of it, was sprung closed and not letting the water through to the pump.I solved this by switching the pump on and by screwing my neck to a crazy angle, managed to get my mouth over the galley faucet. One hard suck and - voila - water.All previous advice looks good too but try this one first. Maybe you will need a short length of garden hose instead of the neck gymnastics.Good luck.

 

[Jose Venegas]

Pressure switch

Some pumps have a built in pressure switch that turns them off when the downstream pressure reaches a pre-set value. In other pumps the switch turns off a relay which in turn turns off the pump. If that relay got stuck in the closed position while the pump ran for a long time, even if you have now water in it the pump will keep pumping after the pressure reaches the pre-set level. As the pressure exceeds that level, the pump should begin to work hard and slow down but it may keep pumping if there is a small leak. For example, the water heater pop off valve opens and allows water to escape slowly. Do you find fresh water in your bilge? Since you report good flow (and I imagine pressure) I doubt you have a blockage upstream of the pump. Does your pump slow down after a while? If it does not, it may have an incompetent valve that prevents it from generating enough pressure to turn itself off but it can still generate enough flow at lower pressures. I doubt that is the case unless your second pump has the same problem.Good puzzle, let us know how you fixed it.