Fresh Water Pump won't self-prime...any tips?

[scraph]

Whenever I run my freshwater system dry...the pump will not prime itself after refill. I am able to establish prime if I disconnect the outlet while the pump is running. Otherwise, the pump will just run continuously and not build pressure. Disconnecting the outlet is not a good option because I developed a leak the last time I did (easily repaired but ... still).

I'm considering installing a valved vent immediately at the pump outlet ... anyone have any better ideas? It really shouldn't be a question of pump head ... the water pump and tank are mounted at the same level. While I'm not providing positive pressure that way, the pump specs say it should be able to prime at something like 5 feet of head.

[scottyt]

okay first check and filters or screens. then make sure something is open to let the air out and the water in... ie open a faucet. next would also check the pump, if the diaphragm has a pin hole it wont prime but will pump once it does.

last option would be to lower the pump if you can.

also you could try putting a manual pump at say the head sink, that would allow you to pump a little vacuum into the system. my boat has faucets that work with pressure or as a pump, you might want to look into something like what i have

[klem]

If you open up a faucet, it should be able to prime. If you don't have something open, it will not be able to build enough pressure just trying to pump air so it will never reach the shutoff pressure.

If you have a small air leak between the tank and the pump, this can make it hard to prime as well.

[sailingdog]

Might also want to check the vent line in the water tank. If it is obstructed, it might cause enough of a problem that the pump won't prime.

[ianmchenry]

Just solved this problem on our Beneteau Oceanis 351 by removing the water line leading into the pump, sucking through the water, and putting it back on the pump. Then did the obvious - opened some faucets and turned the pump back on. No problem.

Cheers,
Ian McHenry

[RichH]

Use a wet/dry shop-vac. Attach the wet vac to a spiggot, start the vac, start the water pump.
Next time you locate a 'water system' pump, locate it at the lowest level possible ... so that its always 'flooded' and doesnt need to be 'primed' when in its old age and pump is 'slipping'. Youll need to install a valved drain for emptying and to remove water which would freeze, etc.