One-way or check valves in bilge pump line

Foswick · Thursday at 2:14 PM

I think the reduction is probably a valid concern, but I wonder if that could be mitigated by inlining an oversized valve ... if that makes sense. So, let's say your discharge hose is 1". You might use a couple of reducers to put a 1.5" check valve inline. Intuitively, it seems that would reduce the back pressure or at least improve net flow, but I am not sure it would. Maybe?

But for me, the concern greater than back pressure is the possibility of the valve clogging/sticking. Bilge pumps are pretty generous about what they will pump through, and I would be concerned about all manner of weird stuff making its way into the check valve and accumulating. (For me, it would be dog hair.)

My sense is that you are the kind of person that would inspect this, from time to time, so that might be OK. I am more the personality type to inspect it to diagnose why the cabin is knee-deep in water.

Curious: Is the goal more to prevent accidental ingress of water from outside? Or, is the goal to simply prevent the "backwash" when the pump shuts off and the drain tube empties back into the bilge?

Don S/V ILLusion · Thursday at 3:09 PM

Use the “right” tool for the job. A valve isn’t it! And you won’t know it failed until it’s too late.

Foswick · Thursday at 3:21 PM

dLj said:
Even oversizing, you still have the spring pressure that needs to push the valve open.

Yeah, that's what made me wonder if upsizing would really address that. My reasoning is that, for the same amount of spring pressure, a larger valve would allow more water to flow. I'm just speculating.

But, yes, at that depth I can see why this would be an issue. There must be a way to estimate how much flow reduction to expect from a given valve. (I am out of my depth, on that subject.)

dlochner · Thursday at 3:22 PM

The only time a check valve in a bilge pump system is needed is when 2 or more bilge pumps use the same discharge outlet. Without a check valve it is possible for one pump to pump water from the bilge back into the bilge through the other pump.

Vane pumps are subject to back filling. One solution is to use 2 pumps, one the the typical high capacity vane pump and the second a diaphragm pump that is not subject to back filling because there are check valves built into pump it self.

Don S/V ILLusion · Thursday at 3:33 PM

dLj said:
Ok, what's the "right tool"?

dj

Anti-siphon loop. Placed strategically, it will eliminate any significant back flow while not prone to failure.

Foswick · Thursday at 4:05 PM

Don S/V ILLusion said:
Anti-siphon loop. Placed strategically, it will eliminate any significant back flow while not prone to failure.

While I agree that a check valve is problematic, and an anti-siphon loop is good to have, the anti-siphon loop will not help with the problem he is trying to address. It has another purpose.

The only solutions I can see are to either accept the problems that come with a check valve or to do as Dave mentions - add a second pump.

Don S/V ILLusion · Thursday at 5:40 PM

Foswick said:
While I agree that a check valve is problematic, and an anti-siphon loop is good to have, the anti-siphon loop will not help with the problem he is trying to address. It has another purpose.

The only solutions I can see are to either accept the problems that come with a check valve or to do as Dave mentions - add a second pump.

If placed in close proximity to minimize length of the hose, it will definitely help minimize water backflow

thinwater · 2025-05-02T08:14:36-0700

dLj said:
Ok, I thought there had been some discussions on the pro's and con's of putting a one-way or check valve into the line at the exit of the bulge pump. But either I'm not using the right search terms or something, but I can't seem to find anything.

What are people's thoughts on putting a one-way valve near the bilge pump exit in the hose to reduce back- streaming?

Any thoughts on the pro's and con's of doing that?

Certainly one of my concerns is the reduction in flow that has to occur.

More thoughts?

dj

If it freezes in the cabin you will have no sump pump. The bilge water stays liquid because it is in contact with water below the ice, but you can freeze water bottles in the cabin. With no check valve, the water flows back to the sump, but with a check valve it can freeze in the hose because the hose is now holding water. Same reason for no low-loops. My neighbor froze a sump pump line that way and his boat sank at the dock.

Also, check valves can catch debris. That depends a lot on the check valve design (don't use a poppet style, only swing checks, and orient them to swing up). Clean bilges are vital, but even the cleanest bilges can hide debris that only floats free in a knock down or rough weather. You need to plan on some debris.

(Refinery guy. I have a lot of expereince with pumping and sumps in the broader sense.)

(Chesapeake Bay, Deale MD.)

thinwater · 2025-05-02T08:15:45-0700

dLj said:
I tend to keep a relatively clean bilge. But there can be junk that gets down there. At the moment no critters on board so critter hair would not be a problem.

Even oversizing, you still have the spring pressure that needs to push the valve open. Certainly i would not want a smaller diameter there, so that's a point.

I do not have a problem with ingress from outside. I do have a deep bilge, like about 6 feet so the amount of water draining back into the bilge when the pump shuts off is not trivial. It's probably a gallon or a bit more. I'm not overly concerned with it but as I am very much " I like a dry boat" sort - I've been considering putting one in just to keep the bilge as dry as I can.

I have one of those dripless seals, so I don't have any water coming in through my prop shaft. My bilge pump doesn't run often. I actually will throw some buckets of water down there just to make sure everything is running. But that also means that residual water tends to sit there a long time as I have to think about flushing it out, and I'm not so good at that....

dj

p s. I've just redone my bilge systems and need to do final adjustments, hence while I'm working in my bilge, i figured this would be a good time to address this question.

p p.s. my current bilge pimp system is pretty darned fast - I cleaned out my water tanks so had to open up the large inspection ports. That dropped close to 200 of gallons right into my bilge. The bilge pump and hose set-up pumped all of that water out in like 2 minutes. I don't want to slow this system down much. I like being able to move a lot of water out in a very short time...

Never, ever, ever use a poppet check valve on a sump/bilge pump. They will clog. That is not what they are designed for. They are for pressure systems with clean liquids.

thinwater · 2025-05-02T08:18:41-0700

dLj said:
I was actually on friends boat with the diaphragm second pump to get the last bit of water out of his bilge. For me however, it would be a hard install and don't think worth the effort....

Diaphragm pumps can freeze and burst. I've seen it happen many times, including several this winter. They have check valves and the diaphragm space will freeze (and then the pump tries to run but can't). They should be winterized and taken out of service until spring.

Obviously, if the boat is hauled for the winter, the sinking risk does not apply. But the burst pump/valve cautions do.

kloudie1 · 2025-05-02T08:50:45-0700

Not a fan of the check valve, but my experience is that the hose from the centrifugal pump to overboard is about 18-20 feet long in my boat.. Without a check, the pump would cycle incessantly since the bilge on the old H-34 is so small. From Hunter in 1985, there was a poppet check valve in that discharge line; to date, I have had one problem with that check valve in the 34 years that I've owned her. That problem was a 1/2" long piece of insulation from a 14 gauge wire that stuck in the poppet seat. The elastic nature of the insulation allowed it to stick in the seat and made the valve leak back slowly so that the pump was cycling about every 3-4 minutes. That insulation had been inadvertently left in the bilge by the owner (me) not being careful. I am pretty careful now about making sure that the bilge stays free of debris. The dehumidifier and air conditioner condensate drain into the bilge constantly.. the bilge pump is original to the boat.. note that the condensate water and any rain water that is in the bilge is clean and salt free; the boat slip is on a fresh water bayou. Yes, I do carry a spare bilge pump and check valve.
I am not lobbying for or against check valves in the bilge discharge line and I understand the concerns, but if ya know what you are dealing with and work to mitigate the concerns, they can be OK..
Again, my experience... yours may be different.

thinwater · 2025-05-02T11:27:17-0700

On mutihulls the run is never more than 8 feet or so. Curiously, the AC discharge hoses generally just go out the side even on monos, not all the way to the transom. Why are your runs so long?