Non return valve on bilge pump...

[PetiteFleur]

Have discovered that I'm getting water under the engine again after our Dutch trip, when motoring, water is pushed up through the bilge pump outlet, even though I've fitted a swan neck in the pipe work just before the outlet. I've never used a non return valve before - will it compromise the outlet flow? It's a small electric bilge pump which I fitted after the end cap on the heat exchanger broke off and flooded the bilge.

 

[jiris]

I had a similar problem. After some consideration I decided to try a non-return valve, ignoring the advice in the instruction manual against it. It worked well, no dramas. The key is using valve with no spring (I actually removed the spring from a spring-operated valve) to assure as low opening pressure as possible. Spring will cause a high opening pressure causing a drastic reduction in the displacement height of the pump, possibly stopping it from operating entirely.

 

[Daverw]

Our whale pump came with non return valves, they were the small rubber duck bill valves.

 

[martinaskey]

Used a 'duck-bill' rubber non return valve in the outlet line of my electric bilge pump for 10yrs+ with no problem.
M

 

[earlybird]

A small centrifugal bilge pump will develop only low pumping head, so output will be affected to some extent by fitting a NRV, so "suck it and see", (sorry).
Note that the typical NRV will not be entirely proof against some back-flow due to debris etc in bilge water.

 

[RichardS]

I have NRVs integral with all my 4 bilge pumps and they work OK. The only thing that I don't like is that when the pump stops the water in the pipe finds its way back down through the pump and into the bilge so this would suggest that you are not going to get 100% sealing.

Richard

 

[Dan Tribe]

I have a Rule 25 pump to clear the drips from the stern gland which collect in the engine bilge, typicall y about 2 or 3 litres max. This pump wont work against a NRV so I have to put up with spongeing out the pipefull of water left.
I recently found that after clearing the bilge more water collected after a few minutes. A bit of a mystery until I found that the outlet pipe had disconnected from the transom skin fitting. All I was doing was pumping bilgewater to the stern where it then slowly trickled back to the bilge.

 

[LittleSister]

when motoring, water is pushed up through the bilge pump outlet, even though I've fitted a swan neck in the pipe work just before the outlet.

Swan neck doesn't go high enough, then?

 

[earlybird]

Have discovered that I'm getting water under the engine again after our Dutch trip, when motoring, water is pushed up through the bilge pump outlet, even though I've fitted a swan neck in the pipe work just before the outlet.

I missed that point earlier. Sounds like you could possibly set up a syphon if you were unfortunate. I'd alter that arrangement sharpish! A swan-neck is not necessarily sufficient if water is coming over. The pump outlet should be above the water-line.

 

[oldgit]

Our whale pump came with non return valves, they were the small rubber duck bill valves.

+1

 

[ithet]

A small centrifugal bilge pump will develop only low pumping head, so output will be affected to some extent by fitting a NRV, so "suck it and see", (sorry).

The thing is a centrifugal pump does not suck, or even blow. It "throws" the water up the pipe, so any bends, NRV etc are obstructions and will reduce the flow. Notwithstanding this I note that some posters have had success with valves, but the output must have been reduced.

 

[RichardS]

The thing is a centrifugal pump does not suck, or even blow. It "throws" the water up the pipe, so any bends, NRV etc are obstructions and will reduce the flow. Notwithstanding this I note that some posters have had success with valves, but the output must have been reduced.

I understand what you are saying about how centrifugal pumps work .... but don't be fooled. They can easily develop pressures equal to or above the minimum UK mains pressure of 1 bar so anything that can be done with a mains hosepipe can be done with a centrifugal pump. Of course, some centrifugal pumps can develop much higher pressures than a bar.

Richard

 

[PetiteFleur]

Thanks for all the suggestions. The outlet on the transom is about 7" above the waterline which I thought would have sufficient. I fitted the swan neck, with about an 8" loop above the outlet.
I think I'll fit a none return valve near the outlet - any preference as to make? - I've found Jabsco and Trudesign examples after a google search.

 

[Daverw]

Any of the smaller duck bill valves as they have very little flow resistance and no internal spring

 

[ghostlymoron]

I fitted a small electric bilge pump in my stern locker. I had to use a Whale nrv to prevent 'cycling', the output was significantly reduced.