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(no email)
Date: Mon Sep 08 2003 - 11:49:42 EDT
Downsides of bilge line check valves in no particular order and with varying
importance.
1. They stick shut.
2. They stick half shut.
3. They stick open.
4. The valve and trapped water provide enough back pressure that the pump
can't prime if it has an air bubble in it and can't build up pressure.
5. The stick shut again.
6. They restrict flow.
7. They "strain" out debris that might otherwise pass through.
8. They stick shut again.
It has been suggested - Practical Sailor I think - that the volume of flush
back water can be minimized by reducing the diameter of the vertical rise
portion of the outlet plumbing. This does restrict flow but the argument
was it was an order of magnitude more reliable than a check valve and the
restriction was not significantly more than that introduce by the valve.
Despite all that I've used them at times. I've had best luck with the flap
type bronze valves. I mount them vertically so the flap falls shut under
gravity and I remove the internal spring.
You should always loop the exit above maximum waterline and include a siphon
breaker at the top. This serves two purposes. First, the obvious one is to
stop water siphoning back. Second, it allows the water in the exit side to
escape overboard instead of being included in the "flush back" water that
runs into the bilge when the pump stops.
Visit our DIY article on how to improve the reliability of commercial siphon
breakers. Go to http://www.yandina.com/hints.htm#Siphon
Andina Foster,
> Andina,
>
> Refresh what's left of my memory if you would. What's the downside of a
> checkvalve used in the situation we're describing? The possibility that a
> small piece of schmutz (a highly technical term <grin>) might lodge in the
> valve and keep it stuck open? It seems to me that the only result of that
> would be you'd be back at square one dealing with the backflow.
>
> Steve Weinstein
> Hydro-Therapy
> 1981 Cherubini Hunter 33
> Sailing out of Oyster Bay, N.Y.
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