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Old 21-11-2022, 23:10   #1
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Non-return valve on bilge plumbing or not?

Hi,

Iím replacing my bilge pump, through-hole and pipe. Iíve been told I should install on non-return valve near the bilge pump but Iím not 100% sold on the idea due to the possibility of it failing and the system not working. Iíd love some feedback and advice on whether to installing a valve is worth the cost, effort and risk?

Thanks in advance .
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Old 21-11-2022, 23:31   #2
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Re: Non-return valve on bilge plumbing or not?

My bilge pump has a loop at the transom to avoid siphoning should we get knocked down.

the problem is all the water left in the hose forward of the loop runs back through the pump into the bilge, once the pump shuts down.

In another life we had the same problem when pumping uphill on a fire. We used a ball check valve to keep the line charged.

Just installed one for my bilge pump line. no issues.
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Old 21-11-2022, 23:40   #3
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Re: Non-return valve on bilge plumbing or not?

One company's manual says to never put in a non return, another company shows one installed.

There's a possibility of trapping air at the rotor that won't pump against the head of water on the other side of the valve. Maybe the company that shows a valve has a design that can't trap air.

You'll hear lots of other reasons not to use a valve.
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Old 21-11-2022, 23:48   #4
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Non-return valve on bilge plumbing or not?

Quote:
Originally Posted by cal40john View Post
One company's manual says to never put in a non return, another company shows one installed.

There's a possibility of trapping air at the rotor that won't pump against the head of water on the other side of the valve. Maybe the company that shows a valve has a design that can't trap air.

You'll hear lots of other reasons not to use a valve.


Youíve hit the nail on the head. Thereís advice pro and against. Confusing to say the least.

I found similar information regarding whether to install a ball valves on bilge pump through holes. I opted to not install and go down the KISS route.
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Old 22-11-2022, 06:39   #5
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Re: Non-return valve on bilge plumbing or not?

Like so many things, the words “always” and “never” do not belong in this discussion.

Bilge pumps are used for different things, and failures have different consequences. A non-return valve will fail. Just a question of when. And how. It might fail open, or it might fail closed. Especially pumping bilge water, with debris and dirt. For any centrifugal pump, a check valve will reduce the flow rate, how much depends on a lot of things, but it will.

If a non-return valve is needed to keep the ocean out of your boat under any conditions, your plumbing has a fatal flaw and needs to be redesigned. It will fail, someday, and your boat will sink.

If you are using a non-return valve to stop short cycling on a small bilge pump used to remove rainwater, condensation, and other minor incursions of water, sure go ahead. Consequences of failure and reduced flow are tolerable.

For large pumps intended to dewater a boat in an emergency, a non-return valve should not be needed or used.

Other cases fall in between and need their own analysis.
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Old 22-11-2022, 17:58   #6
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Re: Non-return valve on bilge plumbing or not?

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Originally Posted by tronic72 View Post
Hi,

Iím replacing my bilge pump, through-hole and pipe. Iíve been told I should install on non-return valve near the bilge pump but Iím not 100% sold on the idea due to the possibility of it failing and the system not working. Iíd love some feedback and advice on whether to installing a valve is worth the cost, effort and risk?

Thanks in advance .
I have a loop and at the top is a T with a small one way vent so nonsiphon works!
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Old 22-11-2022, 17:59   #7
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Re: Non-return valve on bilge plumbing or not?

I never install a check valve in the bilge pump plumbing. Neither of my bilge pumps have a check valve installed. The do have antisiphon loops near the thruhull. It's a boat and a little water in the bilge does not bother me.
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Old 22-11-2022, 18:14   #8
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Re: Non-return valve on bilge plumbing or not?

Check valves fail, get clogged or both and you will never know until you need it. While opinions vary, facts do not. There are better ways of solving backflow which don’t/can’t fail. Why choose the bad option?
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Old 22-11-2022, 18:23   #9
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Re: Non-return valve on bilge plumbing or not?

The need would come from a smallish bilge, and a hose with a lot of rise that holds significant water, so with the pump shuts off, the level in the bilge rises high enough to cycle the pump back on.
It's better to not have the non-return/check valve. That said, you either need one, or you don't. Install it without the valve. If the pump cycles the check valve is a simple common solution. If your pump doesn't cycle like that, then don't include the valve.
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Old 22-11-2022, 19:45   #10
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Re: Non-return valve on bilge plumbing or not?

I don’t understand how a thorough-hole above the water-line can siphon?? I’m guessing it’s because my boat is a cabin cruiser and many other boats are sailing yachts?
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Old 22-11-2022, 20:08   #11
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Re: Non-return valve on bilge plumbing or not?

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Originally Posted by tronic72 View Post
I donít understand how a thorough-hole above the water-line can siphon?? Iím guessing itís because my boat is a cabin cruiser and many other boats are sailing yachts?
Perhaps you might want two different styles of pumps.
Get something like a "Rule" to move lots of water fast.
A power boat should also have a pump back where the bottom meets the transom, (bow high/stern low when underway, water flows aft),
Also have something like a "Par" to "vacuum" the bilge of residual water, or water that back flows from the centrifugal pump.
As an aside, so many threads could be a lot more on point, and with less back-and-forth discussion if the type/model/whatever, of the boat are described in the beginning post.
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Old 22-11-2022, 20:40   #12
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Re: Non-return valve on bilge plumbing or not?

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I donít understand how a thorough-hole above the water-line can siphon?? Iím guessing itís because my boat is a cabin cruiser and many other boats are sailing yachts?
The OP was asking about a non-return valve, which is different than an anti-siphon valve.

When a bilge is deep in the keel, water needs to be pumped up several feet to the through-hull (which might be well above the waterline). When the pump turns off, there is still water in the hose, and with the pump off, that water flows back down into the bilge. It might be enough water for the pump to raise the water level high enough to start the pump again. That is what a non-return valve prevents. Has nothing to do with siphoning.
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Old 22-11-2022, 22:05   #13
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Re: Non-return valve on bilge plumbing or not?

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Originally Posted by wholybee View Post
The OP was asking about a non-return valve, which is different than an anti-siphon valve.

When a bilge is deep in the keel, water needs to be pumped up several feet to the through-hull (which might be well above the waterline). When the pump turns off, there is still water in the hose, and with the pump off, that water flows back down into the bilge. It might be enough water for the pump to raise the water level high enough to start the pump again. That is what a non-return valve prevents. Has nothing to do with siphoning.

That is my issue. Seven foot lift, one inch hose. I have a non return valve at the bottom. The down side is that the bilge pump has to start pumping against that water weight. If there is an air bubble in the pump it can't develop enough force to overcome that weight without some coaxing. So the solution is to never empty the last couple of inches of water in the sump. The float switch is positioned to do that.
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Old 22-11-2022, 22:29   #14
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Re: Non-return valve on bilge plumbing or not?

Quote:
Originally Posted by tronic72 View Post
I donít understand how a thorough-hole above the water-line can siphon?? Iím guessing itís because my boat is a cabin cruiser and many other boats are sailing yachts?
A client of mine had a converted ocean-going tug/shrimp boat sink in a hurricane when the bilge pump failed and the anti-siphon vent was stuck. Hard wind from one direction was enough to start the siphoning, and the process became irreversible as the boat filled with water and heeled. Happily, they floated the boat back up, soaked the engine with oil, and it went straight back to work. On most boats this sort of through-hull is high enough it shouldn't go under water, but preventive devices are meant to protect against the unexpected.
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Old 23-11-2022, 07:52   #15
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Re: Non-return valve on bilge plumbing or not?

We were half way from Newfoundland to Nova Scotia. The bilge pump outlet was on the transom. 4AM. The sea was rough enough that water was over the floorboards due to no anti siphon loop. Float switch didnít exist. Running the pump continuously fixed that. SCARY.
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