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Old 10-02-2015, 05:46 PM   #1
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How high to mount bilge pump float switch

I'm installing a new bilge pump (Rule 3700), and it does not have an automatic switch built in. This is on purpose -- I wanted a separate float switch (Rule 37A Superswitch). However, in the past I have always had bilge pumps with built in automatic switches, so am not sure of just exactly where to mount the float switch. My instincts say to mount it up a bit, rather than just down at the bottom of the bilge, but not sure how well my instincts are on this matter. Any suggestions will be welcomed.

The pump and the switch will both go to a Rule bilge pump control, with ON, OFF and AUTO, in case someone is curious. And of course wired straight to the battery, in case someone is also curious about that.

Lectures on not buying a Rule pump are fine if someone feels compelled, and I will read them, but I like Rule and have had good luck with them over the years. All things fail eventually, of course, but I have found them to be pretty reliable. Just saying.
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Old 10-02-2015, 06:04 PM   #2
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Why not mount the float switch as low as you can go. That way the most water is pumped out.
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Old 10-02-2015, 06:06 PM   #3
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Why not mount the float switch as low as you can go. That way the most water is pumped out.
I don't know why I feel that it should be mounted a bit higher, since what you say is of course absolutely true. But I just have this spooky feeling that it needs to be a bit higher for some reason. Well, maybe some of the experts will enlighten me. If not then I will mount it low.
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Old 10-02-2015, 06:12 PM   #4
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No lower than the bilge pump. Switch will kick on with little to no water around bilge pump if set lower. Pump could run dry or not turn off. Set at same height (or slightly higher) as pump.
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Old 10-02-2015, 06:22 PM   #5
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No lower than the bilge pump. Switch will kick on with little to no water around bilge pump if set lower. Pump could run dry or not turn off. Set at same height (or slightly higher) as pump.
Agreed. Obviously not lower than bilge pump. Guess an unspoken part of the original question is where the automatic sensor is located on an automatic bilge pump. Up high? At the bottom? Somewhere in between?
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Old 10-02-2015, 06:40 PM   #6
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Mine is about 3" higher than the float switch for the smaller primary pump. It's like that in all 4 locations (8 pumps total).

I assume the logic is, if the smaller primary bilge pump cant keep up with the inflow of water then you really dont want a lot of water before kicking in the big bilge pump.

In all 4 locations both pumps sit on the bottom of the bilge. The float switch for the primary switch is also on the bottom of the bilge. The switch for the secondary big pump is 3" higher. Kapich?
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Old 10-02-2015, 07:34 PM   #7
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I too see a 3700 as a high water back up, not a main, in which case you mount the switch higher. If indeed the main, then mount at the same level as the pump base, that's how the Rules are set up. When in doubt read the instructions!
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Old 10-02-2015, 07:46 PM   #8
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When in doubt read the instructions!
Yeah, that has always been my mantra. But, unfortunately, instructions are not what they used to be back in the old days. The instructions that came with it are in about 14 different languages, plus pictures. I only read one language (English), and the pictures are fine so far as they go, but nuances are not their strong point.

However, having not gotten any indication to the contrary, I am going to head down to the marina tomorrow, tools in hand, and mount the float on the same level as the bilge pump. After that we shall see what we shall see I suppose. Probably RT has a good video to insert, showing bubbles.
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Old 10-02-2015, 07:58 PM   #9
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What George said. Plus that size pump can drain back a fair amount of water when it shuts off. So if the switch is to low the pump will just cycle on and off over and over.

I'd consider shit canning that Rule switch and get an Ultra switch you can count on.
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Old 10-02-2015, 08:56 PM   #10
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Rule 1500, 2000 and 3700 gph pumps are very reliable. They will out last many switches. Possum has a very narrow bilge and I can't get those pumps to the bottom. I have two Rule 750's down low and a 3700 mounted higher. The 3700 has only come on a couple of times in the life of the boat but it really saved the day.
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