Bilge pump not powerful enough to prime?

[Tim Good]

My main bilge pump has decided to not be powerful enough to prime itself and pump the water up and over the anti siphon loop. Here are the facts and see if someone can help:

- voltage under load drops to around 11.8
- cabling is sufficient gauge and connections good
- when in shore power and voltage is increased to over 14 when charging, the pump works and manages to pump enough to get up and over the anti siphon loop
- there is a heck valve within 5 inches of the pump in the bilge
- tested pump in its own and seems to shift a good deal of water.

Thoughts?

 

[earlybird]

The rpm of a DC motor is ~ proportional to the voltage. The head developed by a centrifugal pump is ~ proportional to square of rpm.
Therefore you're losing a lot of head when not on shore power.
The check valve won't help either.

 

[William_H]

You do not say what kind of electric bilge pump. Apparently having in inlet hose point. My experience has been with the submersible type pumps. ie the impeller is below the water level so no suction capability. These type will not pump uless the impeller is submerged. ie no air leaks at inlet. I suspect that yours is a centrifugal pump and as such its suction capability is limited. ie if it is primed with water it may suck up more but is not capable of priming itself to any large degree. ie if there was a lot of water in the bilge the lift distance becomes less and no chance of air leak it might self prime.
My guess is that you want the pump to take out the small amount of water in the bilge and it is unlikely to do that. Use a sponge. If you want to test the bilge pump fro serious use then you would need to put a lot of water in the bilge and test it again. Apologies if you know all this and my guesses are wrong good luck olewill

 

[VicS]

My main bilge pump has decided to not be powerful enough to prime itself and pump the water up and over the anti siphon loop. Here are the facts and see if someone can help:

- voltage under load drops to around 11.8
- cabling is sufficient gauge and connections good
- when in shore power and voltage is increased to over 14 when charging, the pump works and manages to pump enough to get up and over the anti siphon loop
- there is a heck valve within 5 inches of the pump in the bilge
- tested pump in its own and seems to shift a good deal of water.

Thoughts?

You do not say what type of pump, the height it is above the bilge water, the height of the anti syphon loop or whether the check valve is in the pump discharge or suction.

However you imply that it all worked well at one time but does not now. Therefore, I think I would first consider the need for a pump overhaul and also that there has been some deterioration in the electrical connections, not forgetting the negative return

 

[Baddox]

That's a big voltage drop, is the battery shot?

 

[ex-Gladys]

That's a big voltage drop, is the battery shot?

Or more likely corrosion on connections??

 

[VicS]

Or more likely corrosion on connections??

but the OP says, "connections are good"

 

[ex-Gladys]

but the OP says, "connections are good"

but the voltage drops to 11.8V... So although connections may look good, I'd remake them all to check cable corrosion... I recently troubleshot a mate's boat where the voltmeter dropped to 5.1 as soon as the battery switch was turned on. The issue was corrosion in both battery pole connections...

 

[ghostlymoron]

but the OP says, "connections are good"

On what basis, a visual inspection proves nothing.