Bilge pump cycles on-off--check valve? new hose config? - Page 2 - SailNet Community
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post #11 of 15 Old 11-11-2018
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Re: Bilge pump cycles on-off--check valve? new hose config?

Almost certain it's backflow from water still in the hose when the float shuts the pump off. Solved it on one boat with a deep but small area sump with a check valve at the pump. Unforrtunately that also added another maintenance issue as the check swing valve would occasionally stick open or get clogged with stuff so needed to be cleaned out occasionally. Tried a rubber flap check valve but the flap took a set and wouldn't seal completely after a while. Was able to turn the flap over and get ti to seal for awhile but it would eventually begin leaking again. Going to a smaller diameter hose will limit the amount of water that can backflow and might also cure the problem but seem to remember the smallest hose barb on a pump is 5/8" so not much room to downsize. A loop might not work as you'll still have a bit of water in the pump side of the loop flowing back to lift the float or excite the switch again.

Last edited by roverhi; 11-11-2018 at 08:43 PM.
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post #12 of 15 Old 11-11-2018
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Re: Bilge pump cycles on-off--check valve? new hose config?

Agree with others that suggest redoing your plumbing to get it right. Disagree with the suggestion to reduce the size of the hose, which will dramatically reduce the flow. That may not be a problem if you can be assured that you won’t ever need the highest possible flow rate.

Agree that it is likely the backflow probably is triggering the “on” mode, so your best suggestion is to install a check valve. My primary bilge pump had this same cycling issue. It was due to the backflow after the switch shut the pump off. The resultant backflow raised the level in my very slack bilge to the point of triggering the bilge pump back on. I solved the problem with a check valve. Even if the check valve were to leak water back into the bilge, at least it would substantially reduce the cycle frequency.

Part of my problem is that the sump is very small, so the backflow is sufficient to raise the level in the bilge enough to trigger the bilge pump.

Last edited by fallard; 11-11-2018 at 11:24 PM. Reason: Added more info
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post #13 of 15 Old 11-12-2018
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Re: Bilge pump cycles on-off--check valve? new hose config?

I believe the ideal set up is a diaphragm pump set to the lowest pickup point for all convenience pumping, ie. to remove shaft drips, fridge or a/c condensation or other acceptably minor bilge water. Then place a centrifugal crash pump, just slightly above it, in the event you have a serious ingress and need maximum gph.

The diaphragm pumps will inherently prevent backflow, but are usually low volume pumps. The centrifugal pumps don't hold back and it's well known that check valves fail (open and shut, both bad). No need for a check valve on a crash pump hose anyway, it should never have water in it.

Last couple of basics.... be sure to use smooth bore hose to allow for the least amount of flow loss. You may need a loop up to the deck level to prevent a back siphon, when heeling. This can reduce flow, as every pump loses capacity, for head rise. I only use pumps with separate float switches, as the switch is the most likely to fail and I don't like having to replace the entire pump, because of the switch. It's possible, this is exactly your problem. With separate switches, you can also keep both pumps (or their pickups if separate) at the bottom of the bilge and just stagger the height of the float switches.

I also think a high water bilge alarm is a cheap and easy to install safety item too.


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Re: Bilge pump cycles on-off--check valve? new hose config?

Quote:
Originally Posted by Minnewaska View Post
I believe the ideal set up is a diaphragm pump set to the lowest pickup point for all convenience pumping, ie. to remove shaft drips, fridge or a/c condensation or other acceptably minor bilge water. Then place a centrifugal crash pump, just slightly above it, in the event you have a serious ingress and need maximum gph.

The diaphragm pumps will inherently prevent backflow, but are usually low volume pumps. The centrifugal pumps don't hold back and it's well known that check valves fail (open and shut, both bad). No need for a check valve on a crash pump hose anyway, it should never have water in it.

Last couple of basics.... be sure to use smooth bore hose to allow for the least amount of flow loss. You may need a loop up to the deck level to prevent a back siphon, when heeling. This can reduce flow, as every pump loses capacity, for head rise. I only use pumps with separate float switches, as the switch is the most likely to fail and I don't like having to replace the entire pump, because of the switch. It's possible, this is exactly your problem. With separate switches, you can also keep both pumps (or their pickups if separate) at the bottom of the bilge and just stagger the height of the float switches.

I also think a high water bilge alarm is a cheap and easy to install safety item too.
All good advice, IMHO. However, sometimes your bilge configuration dictates compromises. Minne’s strategy works if you have sufficient bilge depth and volume. In my case, the bilge is divided into 10 very shallow (3”-6” depth) sumps that are not connected by limber holes.

My primary bilge pump is in the engine compartment that includes the shaft seal. That is the only area that has seen seawater and once overflowed into the main cabin bilge areas when a new pneumatic switch failed. That switch was replaced by an electronic switch that provides for an easy test. However, the high flow centrifugal pump is a tight squeeze and could not be directly replaced by a diaphragm pump (like my secondary bilge pump further forward).

I could locate a diaphragm pump about 5’ away from its pickup to catch the minor amounts of water, but the bilge pump has only been called to automatic duty twice in 22 years, and neither occasion involved a massive influx, so I think I will stick with the centrifugal pump, electronic switch and check valve in the 1 1/2” output hose. Periodic checks should suffice to verify that the check valve and switch are operable.

My main bilge water problem is the rain water that comes down the mast via the halyard entrance and exit holes. The photo shows the mast step and associated bilge areas. The head is to the left, wherein is located a diaphragm pump to handle the shower sump and act as a backup, manually-operated bilge pump. That pump is on a Y-valve that supports a 12’ x 5/8” “central vacuum” hose that I can use to pump out the numerous compartments in my bilge—primarily the area by the mast step after a heavy rain or two. There does not seem to be an easy way to automate the rainwater removal.
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post #15 of 15 Old 11-12-2018 Thread Starter
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Re: Bilge pump cycles on-off--check valve? new hose config?

@fallard
@Minnewaska
@roverhi

Pulled the pump from the bilge. Hose was dry. Not definitive, but that suggested to me that back flow may not be the issue.
Tested the pump (on auto) in a dry setting with the following results: pump motor goes on for a full second, then rests for two/three seconds, back on for a full second, rests, back on, and this continues. This is the original symptom, however the pump is on the dry now. Hence (I believe) nothing to do with water.

My conclusion is the pump is bad. Because the boat is new, I am going to give this issue a clean sweep and swap in a new unit (same footprint so I can utilize the existing platform screwed into the bilge bottom). I am downsizing from the 750 gph to the 500, but on my 27 ft boat, I thought that difference in spec would be ok.

I'll update this thread when the swap is complete.

Thanks!!

Last edited by Vega27; 11-13-2018 at 01:42 AM. Reason: typo
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