The case of the bilge pump mystery - SailNet Community

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  #1  
Old 10-17-2008
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The case of the bilge pump mystery

I came home from a business trip to discover an inordinate amount of water in my bilge. (leaky window, but I'm working on that too) I turn on the battery and flip on the manual pump switch and the pump comes on, but I notice no decrease in water level. I look over the transom and don't see any water flowing out the through hull. Assuming it is a clogged hose or check valve, I disconnect the discharge hose and run water through it with a garden hose, no clog, the water runs right through. Ok, perhaps the pump is too old and needs replacing, I order the replacement from Defender and mount the new pump. The pump works fine, but still won't evacuate the water after an initial surge of liquid. Hhhmmm??

Here is what does happen, with about two or more inches of water in the bilge, I turn on the pump and an initial surge of water rushes out the through hull and then stops, but the pump is still running like crazy. I shut the pump off and wait a few seconds, I turn it back on and another surge of water. As long as I shut it off and turn it on I get that initial surge then nothing. So I disconnect the hose from the pump, turn it on and water rushes through the nipple and back into the bilge at what appears to be the advertised 800 gal per hour. Reconnect the hose and it stops. Ok, now I'm determined to figure this out, so I pull the hose completely out of the boat thinking that perhaps for some reason the height of the through hull in relation to the pump is the problem, (even though it has worked like this for 30 years and was working fine two weeks ago) Gravity, it's not just a good idea, it's the law! So I reconnect the hose to the pump, lay it on the cabin sole and turn it on, only to have the same result. I can blow through the hose, the pump works fine, but I can't get the water out of the bilge without the on, off, on technique.

Anyone want to take a stab at this one?


JLBJR
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Old 10-17-2008
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Replace the hose. If that doesn't help, got no idea what else it could be.
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Yes, I agree and have been doing some internet research on bilge hoses. Everything I read tells me to avoid corrugated bilge hose, because it cuts the flow by up to 30%, but all the bilge hoses on West Marine and Defender.com are corrugated. What is your take on this? Do you see any problem using sanitation hose?
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Possibly an obstruction like a small piece of plastic. Stays sideways for air and the garden hose, but folds over and blocks the hose with more pressure from the pump?

If you replace the hose, at least cut it open to see what's inside.

Bryan
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An autopsy of the hose, excellent idea!
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I believe your pump may be airlocking. It sounds crazy I know! I work in waste water treatment and we use a lot of submersible pumps. I've seen quite few that would do what you describe, even though they were several feet underwater. On those pumps, if you actually take the time to read the instructions, there is ALWAYS a recommendation to drill a small hole in the discharge pipe (1/8") to allow the pump to flood completely. Every time I have drilled the hole the problem goes away. I'd like to hear what you actually find is the problem, but this is probably worth a shot.
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I read about this one. A guy had a similar problem but it was a head intake.
There was a creature in the through hull. It would let a little water get through then puff up and close the hole. He snorkeled and looked in the hole and it was clear. Looked a second later and it was clogged.

The garden hose may be so much pressure that it can't be stopped.

You may have Tennant's!!!
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Air locking, interesting! Where would I drill the hole in the hose?
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Quote:
Originally Posted by JLBJR View Post
Air locking, interesting! Where would I drill the hole in the hose?
You want the hole as close to the pump body as you can. You probably don't want a hole in the pump itself, in case I am all wet! So I'd drill a small hole in the hose just past the pump barb.

By the way, are you sure your pump has the polarity wired right? A centrifugal pump running backwards will still pump water, but not nearly as much, and they airlock easier. Simple rule for pumps: the liquid ALWAYS takes the longest route through a pump of any kind! So the pump should rotate in the same direction of the longest path.
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I've got the exact same issue. Did you ever solve it?
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