[QUOTE=manonash;10645]

I like the idea of the non-return valve, which makes me wonder - why don't they make automatic bilge pumps with non-return valves? (Or, do they?)

[/QUOTE]

In theory the "non-return valve" (or check valve) makes sense in this application, but there are 2 countervailing concerns
1) the valve could get stuck, and such failure could prevent the bilge pump from doing its job when you really need it, and
2) the backwashing from the remaining water helps clear out obstruction.

Steve,

On our boat, there was a check valve in the output of the bilge pump hose that stuck closed. The pressure from the pump was not enough to open it and my bilge would not evacuate. Fortunately, it was only a few gallons of rainwater down the mast over a few stormy summer weeks, but imagine my surprise when the bilge pump was running and no water was being pumped.

I removed the stuck check valve and all was well.

This strainer is also often called a Strum Box.

My bilge pump is rigged with a siphon-break but no check valve.

Nimue, can you describe the siphon break, I think I see the point, would like to know more?

Nick,
Below is a link to one at Defender's. They come in many sizes, to fit the hose you have.

[URL]http://www.defender.com/product.jsp?path=-1|51|106370|316448|316445&id=102633[/URL]

Very simple in design, and they work well. I also took out the check valve and installed a vented loop in my boat. Look in the Upgrades Section. I wrote an article about installing a second bilge pump, with pix, showing a vented loop.

Hi Tom, did you use the version with a valve atop the loop or the one with a hose barb and exterior venting? It seems that the former would have similar potential problems as the check valve ?

Nick,

The anti-siphon vent closes when fluids are 'pushed' through the hose and opens to allow air to enter in the case where siphoning would occur. That 'breaks' the siphon effect and water doesn't backflow into the boat.

It isn't a check valve that is inline with the hose, where getting stuck prevents water from flowing when you need it to.

I guess I would have to see one to really evaluate it. It does seem that if the valve failed (i.e. opened when "pushing water", or broke), you could be emptying your bilge into your bilge . . . ?

I've just got a new-to-me C36 and there is a scary amount of hoses and random unterminated electrical cables down in the dark dirty depths . . . Trying to trace them all and figure out what if anything needs to be done to each.

By the way I tried to access the Upgrades section to check Tom's article but I get a page that says "There are currently no posts in this category" . . . any advice on that?

Thank you!

Nick,

If the anti-siphon valve would fail 'open' you would leak a small amount of water back into the bilge, but it would be a pretty small fraction of what was exiting the boat.

Failing 'closed' would not affect pumping out, but would negate the anti-siphon feature in the unlikely event the discharge of the bilge pump hose was underwater and a backflow started.

Nick,
To view the Technical Sections (specifically the Upgrades), you must be a Member of C36/375IA. Here's some more info about that:
[URL]http://www.c36ia.com/node/698[/URL]

Many people have said it's the best money they have spent on their boat. Join for 3 years and you also get a free Tech Notes CD, with TONS of info on it, and over 40 owners manuals.