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Old 07-02-2008, 22:16   #1
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Question Bilge Pump Float Switch Arrangement

The automatic feature of my aft bilge pump was not working. PO had installed 3 float switches on a vertical plane - actually mounted to an old batten fastened so that to repair you just remove a bolt and lift the whole thing up out of the bilge.

Anyway, top switch is for an alarm. Middle and lower switches have me confused. All are wired to a 12vdc relay inside an electrical junction box. Looks like the relay itself is bad. I can manually close the contacts and the pump runs. Meter across the float switch leads tells me the switch is bad.

New switch installed and since the relay is bad I just wired it the old-fashioned way, between the power source and the pump. Works fine EXCEPT that it now short-cycles. The discharge hose run is quite long and the water draining back into the bilge when the pump stops is enough to activate the switch again.

I suspect that the old relay unit was an arrangement where the middle float switch (now unused) would start the pump, and the lower switch would shut it down when the water got to the low limit. That way the hose contents draining back would not restart the pump. Since I don't think they make a choice of normally closed or normally open float switches, the relay had to be the key.

Solid state I know this calls for an SCR - once trigger voltage is applied via the mid-level float it would run until main voltage is removed by the lower float switch. Do they make one or do I have to build it?

I don't have a schematic and there's no stamping on the relay, which seems to have 4 primary and 2 secondary terminals.

Since I'm sure this is a common issue with bilge pump drain-back, I'm hoping there's a wiring scheme or specialized controller to handle this? Maybe a neat-trick way to wire a pair of float switches to accomplish this?

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Old 07-02-2008, 23:14   #2
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I believe most of the electronic switches have a delay for this purpose. I haven't used Water Witch, but they have a 14 second delay.

http://www.waterwitchinc.com/techshe..._techsheet.pdf


The relay is probably wired this way. It is a circuit used with equipment that once power fails, the equipment stays off until someone pushes the on button again
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Old 08-02-2008, 00:16   #3
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Why not install a one way valve in the pipe run close to the pump? Might be a simpler solution.
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Old 08-02-2008, 00:39   #4
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Why not install a one way valve in the pipe run close to the pump? Might be a simpler solution.
JOHN
Has anyone done this for this purpose? I know it's been done to keep your boat from sinking with an under the waterline outlet. With the parts that I envision using this would cause the pump to cycle almost as before, but with long random delay times between cycles. What I'm assuming is a centrifugal bilge pump and the rubber flap valve that provides low restriction that you see next to the bilge pumps on the shelves. I can't see that this valve would seal perfectly, at least not for very long. So the water in the hose would eventually wind up back in the bilge tripping the pump back on, just not immediately.

Anything other than below, I would expect to have too much backpressure for a centrifugal pump to work well.

West Marine: Nylon In-Line Check Valve, For 1" Hose. Product Display

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Old 08-02-2008, 01:58   #5
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Since I don't think they make a choice of normally closed or normally open float switches,
Hi Mark, not true check this out.
Barksdale Inc | Level Switches - Bilge
And take a look at the Data Sheet.

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Old 08-02-2008, 06:11   #6
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...I can't see that this valve would seal perfectly, at least not for very long. So the water in the hose would eventually wind up back in the bilge tripping the pump back on, just not immediately...
My feelings exactly. I don't like those back-flow preventers in a bilge line.

I know this system design worked at one time - that's what drives me nuts. No check valve in the system. I'm going to pull the relay and see if I can figure out its design for primary / secondary contacts.

Morgan Paul - thanks for that link to the Barksdale site. That may be a much more elegant solution - even if it does cost almost 3 times as much. 316 stainless and less worries might just be the thing...

This still has to be a common problem for boaters. What am I missing?
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Old 08-02-2008, 06:57   #7
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I would try raising the switch or lowering the pump. Make sure you do not have a loop in the discharge hose. Do you have smooth hose? The corrugated hose could hold more water in it that could run back into the bilge.
You will find the answer.

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Old 08-02-2008, 07:42   #8
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I would try raising the switch or lowering the pump. Make sure you do not have a loop in the discharge hose. Do you have smooth hose? The corrugated hose could hold more water in it that could run back into the bilge...
Tried raising the switch already. Only about 1 inch though. The bilge pocket is the same dimension for quite a bit of depth, so I don't expect this will do anything except leave more water in the bilge while it short-cycles the pump. Hose is smooth type.

I'm thinking I need a switch with a larger arc of movement - this one says On at 2" off at 3/4".
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Old 08-02-2008, 08:23   #9
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I'm thinking I need a switch with a larger arc of movement - this one says On at 2" off at 3/4".
The manufactos of "Ultra Junior" makes a switch for deep bilges and long hose-runs to avoid cycling:
PUMPSWITCH PRICES

Look for model UPS-04
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Old 08-02-2008, 09:04   #10
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The Ultra Pumpswitch High Differential # UPS-02 has a 2-1/4 inch “On-Off” differential (compared to the standard 1-1/4"), which helps reduce cycling.

I really like the “UPS” products, particularly the UPS-01 c/w H.W. Alarm contacts.

I don't recommend (nor does ABYC) Check Valves in B.P. systems.
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