Check valve for bilge pump just inside the hull.

[Privilege]

My catamaran has a number of bilge pumps. The discharge hoses loop high in the compartment and then discharge not far above the waterline. The trouble is, on a rough day, water sloshing against the side of the hull can be forceful enough to squirt water through the discharge hose back into the bilge. I know that check valves are sometimes used just upstream of the pumps but I do not consider this a good idea (reduced flow, air locks etc...). I assume that a vented loop will prevent a siphon problem but won't stop the forced water as I have described?

Is there any harm in putting a check valve just inside the hull? The outgoing water is already on its way 'downhill' by then so it will have a very minimal affect on the discharge rate and the valve will prevent water from going the wrong way.

[colemj]

We have them installed exactly like you are contemplating. Another idea is to put flapper valves on the outside of the thruhull if convenient to do so.

Mark

[David M]

You do not want to put a check valve in your bilge discharge line. They can stick closed. I like the idea of a taller loop or an external flap valve or both.

[colemj]

For clarity, the type of check valve we put in was a tube with a rubber flapper in it that can rest against a stop. The valve is pointing down - so the flapper is always hanging open until a wave pushes into the thruhull.

I don't see anyway this can stick closed, and the resistance to pumping is miniscule.

Mark

[alctel]

I'd advise against putting any kind of check valve on your primary 'oh ****' pump

For a secondary or nuisance water bilge pump, sure

[Privilege]

Mark,

I agree with you. Bearing in mind that we are not talking about a check valve near the pump, I don't see that the rubber flapper can be any more prone to jamming than would a flapper on the outside of the thru-hull.

[peghall]

Why wouldn't a clamshell cover over the thru-hull work?

[colemj]

Originally Posted by peghall

Why wouldn't a clamshell cover over the thru-hull work?

It can, as well as one of those external flapper valves I mentioned earlier. In our specific case, neither of those will work in the location of the thruhull that needs it, so I put in the in-line flapper valve. Other thruhulls on our boat have either a clamshell or an external flapper.

Mark

[colemj]

Originally Posted by Privilege

I don't see that the rubber flapper can be any more prone to jamming than would a flapper on the outside of the thru-hull.

It won't be, and it will have the added benefit of lasting longer.

Mark