Manual bilge pump won't prime

[Modulation]

I've just spent a frustrating 3 hours taking my Plastimo pump apart and cleaning it out. It's a standard diaphragm type with inlet and outlet valves. It just wouldn't take any water out of the bilges - I didn't know it wasn't working as I normally use the electric pump. However I don't feel comfortable relying solely on an electric hence trying the manual one with about 5 or 6 inches of cover to the hose end . Wouldnt work so I tried it in a bucket of water to get about 12 inches depth for the hose. It pumped for 5 or 6 strokes of the pump handle and then stopped. It seems to "suck" on one stroke of the handle but ejects the water on the other stroke. The pump innards and gaskets are all fine and no leaks. For info the pump is mounted about 4' 6" above the bilges.
Oh and the pump works fine when I fit a short hose to it and ask it to empty a bucket just beside it. And the hose to the bilges is ok too as I have just used a friend's portable pump with it and it pumped fine.
I'm perplexed, Any ideas??
Thanks

 

[sailorman]

fit a strum box with a non return valve.
my manual pump is some 12ft away from the bilge & 4ft higher

 

[VicS]

I've just spent a frustrating 3 hours taking my Plastimo pump apart and cleaning it out. It's a standard diaphragm type with inlet and outlet valves. It just wouldn't take any water out of the bilges - I didn't know it wasn't working as I normally use the electric pump. However I don't feel comfortable relying solely on an electric hence trying the manual one with about 5 or 6 inches of cover to the hose end . Wouldnt work so I tried it in a bucket of water to get about 12 inches depth for the hose. It pumped for 5 or 6 strokes of the pump handle and then stopped. It seems to "suck" on one stroke of the handle but ejects the water on the other stroke. The pump innards and gaskets are all fine and no leaks. For info the pump is mounted about 4' 6" above the bilges.
Oh and the pump works fine when I fit a short hose to it and ask it to empty a bucket just beside it. And the hose to the bilges is ok too as I have just used a friend's portable pump with it and it pumped fine.
I'm perplexed, Any ideas??
Thanks

one or other (or both) of the valves not seating/sealing properly !

NRV on the suction will solve the problem if its the suction valve. An NRV on the discharge will solve it if its the outlet valve at fault

 

[VicMallows]

Or a leaking diaphragm?

 

[omega2]

STICK YOUR HAND OVER THE "OUT" and pump

 

[Modulation]

STICK YOUR HAND OVER THE "OUT" and pump

I like the simplicity but but what does it do?

 

[VicS]

I like the simplicity but but what does it do?

It'll stop it sucking air in if the discharge valve is dicky. ....... and make you hand wet if it does pump.

 

[sailorman]

I wonder what worked

 

[VicS]

I wonder what worked

No you dont . My guess is you know as well as I do what worked.

 

[sailorman]

 

[Modulation]

The strum box with the nrv worked. Fitted it yesterday and it worked straight away, so it is/was the nrv in the pump entry. So thanks one and all!

 

[charles_reed]

The strum box with the nrv worked. Fitted it yesterday and it worked straight away, so it is/was the nrv in the pump entry. So thanks one and all!

Good of you to afford closure to all the contributors.

 

[SputnikLife]

The strum box with the nrv worked. Fitted it yesterday and it worked straight away, so it is/was the nrv in the pump entry. So thanks one and all!

Glad to know your issue got fixed. I have a similar issue. My pump won't pump. For my info what is a strum box and NRV?

 

[john_morris_uk]

Glad to know your issue got fixed. I have a similar issue. My pump won't pump. For my info what is a strum box and NRV?

A strum box is the name given to a filter on the end of a pipe in a bilge. (The pipe obviously leads to the bilge pump.) NRV stands for non return valve.

 

[SputnikLife]

A strum box is the name given to a filter on the end of a pipe in a bilge. (The pipe obviously leads to the bilge pump.) NRV stands for non return valve.

Oh I see thanks so much for the info John

 

[Buck Turgidson]

Ive got an old henderson Mark 3 that requires a great deal of encouragement to get going. new seals and rubber flap valves made little difference. does anyone know off hand if the MK5 is a drop in replacement or are the mounting points different. The handle is through the cockpit side wall.

 

[TernVI]

Manual bilge pumps are basically very poor at pumping air.
One particle of dirt in the valves and they don't prime, especially when dry.
One thing that helps is to be able to hold your hand over the outlet skin fitting, as an extra valve. Also, squirting a drinking water bottle down the outlet often works.
I race boats which depend on bilge pumps, we have to do this quite often even with pretty new pumps.
Pumping really fast also often helps.

A pump which doesn't have to lift water far to wet the valves will be more reliable.

 

[trevbouy]

Glad he fixed it 5 years ago.

 

[andsarkit]

Ive got an old henderson Mark 3 that requires a great deal of encouragement to get going. new seals and rubber flap valves made little difference. does anyone know off hand if the MK5 is a drop in replacement or are the mounting points different. The handle is through the cockpit side wall.

My Mk 3 is the same but is fine once primed. You could check for air leaks in the suction pipe or a small split in the diaphragm. The alloy housing does corrode and might not seal on the diaphragm.
The flap valves can be pulled off (no need to undo the little screws) and reversed.
Can't help with the dimensions of the mk 5 but at the worst you will need to drill a few holes that will be not be seen behind the panel.