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Automatic bilge pump - non return valve advisable or redundant?


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Be careful with non return valves on bilge pumps. I had an issue with one a few years ago, upon testing by pooring a few buckets of water in it would turn on and pump water out. Then after 30 mins added another bucket of water, pump would turn on but not be able to pump...  Turns out there was an air lock on the pump impeller!! As the bilge water level rose the air in the impeller had no where to go as the non return valve had 2 foot of water on it...

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12 hours ago, Arthur Marshall said:

And bear in mind that in thirty years of boating I have always bought good quality automatic bilge pumps, and on every occasion when they should have worked, they haven't. Result, one sinking, two near sinkings. I still have one, but I wouldn't trust it and am surprised so many do.

Sorry, why do you still have one then?

9 hours ago, Quattrodave said:

Be careful with non return valves on bilge pumps. I had an issue with one a few years ago, upon testing by pooring a few buckets of water in it would turn on and pump water out. Then after 30 mins added another bucket of water, pump would turn on but not be able to pump...  Turns out there was an air lock on the pump impeller!! As the bilge water level rose the air in the impeller had no where to go as the non return valve had 2 foot of water on it...

Thanks a lot. This is the kind or problem I was wondering about when I first though of it. Air locks or some kind of "suction" effect.

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17 hours ago, Steve56 said:

On the other hand how do people feel with the newer types of automatic pumps that do not have a float but rely on water sensing.

On my salty water boat I've used one of the sensing ones that starts every 5 minutes or so and monitors the load to check if it's pumping anything or not, it's been on there for about 5 years. This year, with lockdown and not being allowed in the marina, is the only year I've ever had it on 'automatic'. It's worked flawlessly, but the battery is permanently connected to a CTEK charger, so no risk of flattening anything.

 

If it hadn't been connected to a charger then I'd have been reluctant to leave it running for weeks on end.

 

3 pumps on the nb, 1 with float switch under the engine and 2 sensing, 1 in the front well deck and 1 in the BT tube, never heard any of them ever run. I tend to go around with a battery powered hand pump every so often, so the water level has never been deep enough to trigger them.

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More expensive but the whale supersub pumps look really good. I just bought two for the stern tube drip bilges (twin engine boat). The automatic ones, which have an internal sensor of some sort and have a joker valve  in the outlet.

 

The boat hardly takes in any water but stern tube drips do accumulate and overflow into the engine drip trays so a couple of little supersubs seems sensible. Stuck down with magnets. 

 

If I had a boat which regularly took on water I would install an auto bilge pump in addition to one running on a timer mounted a bit higher which operates regardless of whether there is water or not. That way if the auto fails for any reason your timed switch does a cycle anyway and takes away the major risks. 

 

Obviously potential problems with dry running pump so you probably would ideally want it to run for a short time regularly. Easily achieved with a programmable 12v timer switch. 

 

 

Or just run the same pump through a timer as well as the float switch. 

 

Maybe two pumps is overkill. 

 

Edited by magnetman
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  • 1 month later...

On our other boat (lumpy water catamaran) we have a total of nine bilge pumps:

 

In each hull there's a Whale gulper connected to a downward facing strainer that (slowly) pumps out water to within a few mm. This is wired via an on/off/auto switch. In auto mode a float switch operates the pump. This low capacity pump is backed up by a 3000 Gph impeller pump wired via an on/off/auto switch. In auto mode a water sensing switch operates the pump.

 

Each engine room has the same setup as above except instead of the Whale gulper a small capacity impeller pump is fitted instead (plus a 3000 Gph backup pump).

 

There's also a manual lever operated (frightened man) bilge pump located in the cockpit with a roving hose long enough to reach each hull or engine room.

 

With regard to people being concerned about inoperative float switches, either do as I have done and fit separate pumps & switches/sensors (but our boat is designed to sail offshore) or wire two float switches in parallel to a single bilge pump - a much cheaper solution. The pump would then operate in the event of either float switch being triggered.

 

Edited to add: when I said "our other boat" - we don't yet have our other boat. We have been told that the build of our narrowboat shell has been delayed by a month due to Covid.

Edited by Jackofalltrades
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On 14/03/2021 at 13:28, Jackofalltrades said:

or wire two float switches in parallel to a single bilge pump - a much cheaper solution. The pump would then operate in the event of either float switch being triggered.

 

Doesn't help if a float switch gets stuck 'on' and the pump runs continuously until the batteries are flat or until it is wrecked through running dry for a long time.

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34 minutes ago, David Mack said:

 

Doesn't help if a float switch gets stuck 'on' and the pump runs continuously until the batteries are flat or until it is wrecked through running dry for a long time.

 

If a float switch activates the bilge pump to remove water that shouldn't be there then I'd take the risk of flat batteries or a wrecked pump because the other alternative might be a sunk boat.

 

But the risk of of a float switch getting stuck on is, I suggest, minimal, and can be mitigated by regularly checking it is operating correctly and nothing can foul it. During these checks it's more likely that a corroded wire or dodgy connection will be found. I check stuff like this regularly on the lumpy water boat. I expect I'll do the same on the narrowboat. All part & parcel of the preventative maintenance checks that come with having a boat. Some people don't bother. Some get lucky. Others... well we've all seen the results.  I prefer to stack the odds in my favour.

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On 15/01/2021 at 15:38, BEngo said:

 

Better to ask a reliable mate, or your marina, to keep an eye on it and pump if and when needed.  Filling with water is not the only problem that can arise  when your boat is left for some time so they can look out for other problems too.

 

 

Are the two options mutually exclusive? One may indeed be better than the other, but I don't see why that should stop the OP doing both.

 

My advice is do what you can yourself and also ask others to keep an eye on your boat.

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