Originally Posted by Hartley18
Agreed, you need to prevent back siphoning which includes a high loop and a siphon break.. but you're quite wrong
about having the check valve up high defeating the purpose. Hose drain back is irrelevant - it's, what, 1 litre of water max?
Think about what happens when you put the gunnel under on a flush-deck boat with the bilge pump exit out of the side just above the waterline - even with a high loop and a siphon break.
Boats have sunk because of that.
What is "quite wrong"
is an installation like you state.. Sorry but I can't fix an improperly designed bilge pump system. As I said and was discussing in a "PROPERLY" designed bilge pumping system, which on sailboats does NOT include placing the exit where it will go under water under heel and can't be protected by a siphon break, there is no need for a check valve.
Sorry but if you have a boat designed like this to rely on a $0.50 piece of rubber flapper is just crazy. The US ABYC recognizes this and specifically prohibits check valves used for this purpose. This is a situation that requires surgery, don't put a Band-Aid on it.
An installation such as that does not meet even the basic safety standards.
22.8.6 The discharge location shall be above the
maximum heeled waterline, or
22.8.7 the discharge may be located below the
maximum heeled waterline if the discharge line is provided
with both of the following:
18.104.22.168 a seacock installed in accordance with the
requirements of ABYC H-27, Seacocks, Thru-Hull
Connections, and Drain Plugs, and
22.214.171.124 a vented loop or other means to prevent
siphoning into the boat. A check valve shall not be used for