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Old 05-06-2017, 15:00   #1
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Bilge pump cycles on/off too rapidly

Problem: after the pump empties the bilge it turns on again after a short time.

System: Remote pump, strainer and scissor switch in bilge to activate.

Thesis: After the pump operates some of the water drains back into the bilge and is sufficient to reactivate the pump.

Check carried out: holding the float in the bilge up manually to keep the pump running until nearly all of the water has been evacuated. That makes the cycle much longer but is not an effective cure.

Questions:

1. Is there any way to prevent the back flow of water?
2. Is there any way to adjust the scissor switch? (I cannot see one)
3. Is there any other cause or solution to the problem?
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Old 05-06-2017, 15:03   #2
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Re: Bilge pump cycles on/off too rapidly

Raise activation switch a little to allow for back flow?
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Old 05-06-2017, 15:53   #3
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Re: Bilge pump cycles on/off too rapidly

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Originally Posted by mike d. View Post
Raise activation switch a little to allow for back flow?
I thought about that but logically it is not going to help. Wherever the switch is the difference between water in and water out is going to be the same. The switch closes on its own base and not the base of the sump.
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Old 06-06-2017, 13:23   #4
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Re: Bilge pump cycles on/off too rapidly

If you can get at the sump feed, could install a check valve? You would have to relieve valve in winter! A flapper type valve would probably be best, as there is no spring pressure for the pump to over come!
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Old 06-06-2017, 13:51   #5
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Re: Bilge pump cycles on/off too rapidly

A check valve will solve the problem, but they can create other problems. I try to avoid them.


I'm assuming your sump area is quite small, so a small amount of water causes a significant rise in level making the switch trip. And/or you have a fairly large bilge pump with a large diameter hose which holds a significant volume.

I'd suggest putting in a small bilge pump at the base of your sump with a small diameter hose. Only a small amount of water will return at the end of the pump cycle.

Install your existing large pump with large hose slightly higher in the sump. It with remain high and dry (and clean) until needed to handle a more serious issue. You could even tie in an alarm which buzzes when this pump runs.
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Old 06-06-2017, 14:59   #6
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Re: Bilge pump cycles on/off too rapidly

Bilges are meant to be dry most of the time. You can manually remove the little water that comes back from the pump (sponge, hand pump or a child's water gun pump). Then make sure you eliminate any water that drains to the bilge (plug the fridge, install a shower pump, check for leaking water fittings or safety valves (once I had a water heater safety valve leak slowly).

Another solution is to install a small diaphragm pump in parallel to the main pump.
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Old 07-06-2017, 10:26   #7
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Re: Bilge pump cycles on/off too rapidly

Kokanee has the best answer, but some new bilge pumps have a rubber check valve built in like some shower sumps. This holds the water in the hose. Check valves can be dangerous without a vented loop. If debris gets into the check valve, it can be held open.
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Old 08-06-2017, 05:33   #8
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Re: Bilge pump cycles on/off too rapidly

I avoid check valves. They seldom work 100% efficiently and just take longer to allow the water to seep back into the bilge. There are a couple of options you can consider; use a Atwood S3 electronic bilge switch or similar. They are pretty cheap but in my experience are much more reliable than mechanical bilge switches. Once activated and when the water falls below the sensor level, they stay on for one minute allowing your pump to fully drain the bilge. Walmart and Amazon sell them for $22.00

https://www.walmart.com/ip/Attwood-S...756#about-item

Another option for you is to install a diaphragm pump instead of a centrifugal. (Such as the Whale Gulper 220). They can be mounted higher and suck water up from a small bilge area. They can be run dry and will get out more water than a normal pump. However, they don't move as much water as a centrifugal so don't have it as your primary emergency pump.
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Old 08-06-2017, 06:49   #9
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Re: Bilge pump cycles on/off too rapidly

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Originally Posted by Alita49DS View Post
I thought about that but logically it is not going to help. Wherever the switch is the difference between water in and water out is going to be the same. The switch closes on its own base and not the base of the sump.
Yes the volume of water that backflows is the same. But most bilges aren't square and the sides are tapered. If yours is the volume per height as you go up increases. So the backflow is a smaller percentage of the cycle volume.
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Old 08-06-2017, 07:12   #10
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Re: Bilge pump cycles on/off too rapidly

Never install a check valve in a bilge pump line.

For emptying bilge install a diaphragm pump higher than the outlet and install its float switch lower than that of the main pump. Keep hose runs short as possible.
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