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Old 08-04-2010, 01:40   #16
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Not all pumps work the same. A centrifugal pump with air trapped in it due to the check valve can develop insufficient pressure to push the weight of the water in the hose above the check valve out. A completely different story from your diaphragm pump.

Post #5 in particular:
Bilge pumps


Quote:
Originally Posted by bobfnbw View Post
Far as I know there is not reason you can't install a check valve in a bilge pump circuit. I did. And am glad of it. Now I would not do that If I only had one pump, I don't. But my primary bilge pump is a jabsco diaphram pump and I installed a one way valve to keep water from returing after the pump shuts off. Works fine.
I also have a loop with a vent. Works fine. I use a strainor inline before the pump and a groco strainer in the bilge as well.
As to the Origianal question, mount the primary on the transom. Double clamp it.

Gord, this to me says not to use the check valve in place of a vented loop, not don't use a check valve at all.

22.8.7.2 a vented loop or other means to prevent siphoning into the boat. A check valve shall not be used for this purpose.
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Old 08-04-2010, 06:22   #17
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Your interpretation may be technically correct, in that they (ABYC) are not issuing a flat prohibition against check valves in bilge pump piping.

ie: “H-22.8.9 A check valve may be used only when necessary to prevent an automatic bilge pump from cycling on and off*
due to back flow from the discharge line.”

*This would not include annoying back flows that don’t cycle the pump ‘on’.

Check valves are notorious for failing in both the open and the closed position, which respectively leads to flooding or failure to pump.

When used to prevent backflow pump cycling (as permitted above), ensure that the check valve is not too close to the pump.
If the valve is too (particularly in longer discharge runs) close to the pump, the pump may not be able to overcome the weight of the water on the discharge side of the valve, rendering the pump ineffective/inoperable.

See the Rule Instructions, for instance, which specify a Vented Loop, and NO Check Valves.

Here ➥ http://www.rule-industries.com/files/itemdoct6041.pdf
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Old 08-04-2010, 06:36   #18
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Okay guys thanks for allaying my fears. The install manual for my Rule while being rather cryptic says you should stick the hole about 12 inches above the waterline. Mine is probably more like 18. I do have the luxury of running the loop up into the inside of the coaming well above the waterline and the hole. I did try it with the check valve in place and did run into some of the problems you guys are mentioning. The back-flow isn't bad enough to re-trigger the pump just enough to keep things sadly damp down below.

Sorry for the panic. I am such a spazz. Not very salty of me at all.
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Old 08-04-2010, 07:07   #19
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Quote:
Originally Posted by unbusted67 View Post
... The install manual for my Rule while being rather cryptic says you should stick the hole about 12 inches above the waterline...
The Rule manual, to which I linked, indicates 12" above HEELED waterline (page 13).
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Old 08-04-2010, 07:35   #20
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Yup, I put the hole in the transom though. I hope I won't be heeling in that direction!
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