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post #1 of 11 Old 01-04-2011 Thread Starter
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Bilge pump switch

I have two bilge pumps, one 600 gph one controlled by a switch, and a 2000 gph above it that I can turn on manually. When the 600 gph one died like they often do, I replaced it but the new one had a larger output hose. Of course, I just got some larger hose, but then found I had a problem: the low point of my bilge is in the keel, a rather small area. So when the bilge pump has pumped it out it shuts off and the water left in the larger hose runs back down into the bilge and turns it on again... indefinitely - or at least until the pump burns out.
I measured the rise in bilge water from what's contained in the hose and it amounts to about 6 cm - more than any of the switches I can find can handle. I can get a second switch and wire the two switches to a relay in a "latching" arrangement but was wondering if anybody had any better ideas. The space in the keel is small, so the less junk I put down there, the better.
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post #2 of 11 Old 01-04-2011
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You need a check valve in the outlet hose close to the pump.

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post #3 of 11 Old 01-05-2011
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I would avoid the check-valve option if you can. They eventually get stuck partially open, in which case they're useless, or get clogged, in which case they render your pump useless. Just use an adapter to neck down the outlet to a reasonable size (i.e., what you had before, or maybe a bit smaller). The smaller pump is just there to take care of the occasional drips, condensation, spilled beer, etc., and only needs enough water flowing through it to keep its bearings lubed. It doesn't really matter if it takes a minute (with the smaller hose) rather than 30 seconds (with the larger hose) to empty the bilge once a day (or week, or month); the 2000 gph pump is the one you want to make sure can run at its full capacity when needed.
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post #4 of 11 Old 01-05-2011 Thread Starter
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I had a check valve but got rid of it for the reasons already mentioned, besides which those things do leak a bit so it would just slow down the cycling. I had thought of necking down the output to the 3/4 hose I had before but figured there must be a reason for the larger size and did not want to increase the backpressure on that pump. And yes, the small one is there for just the little bit of water that comes in sometimes - I think mostly rainwater down the mast from various openings in the frequent tradewind showers we get here.
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post #5 of 11 Old 01-05-2011
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I don't think the back pressure really matters. As far as the pump is concerned, any back pressure from a smaller outlet is just like having it mounted so that it had to pump against a relatively large head.
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post #6 of 11 Old 01-05-2011
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Generally, the best option is to have the float switches/bilge pumps mounted at different heights. The lowest one should be the 500 GPH "maintenance" pump... this one is the cheap, heavily used, easily replaced model that does most of the pumping. Then you have a much higher-capacity one mounted about an inch or two higher than this one... that does the "dewatering" for emergency situations.

This keeps the amount of water in the bilge at a minimum, since the 500 GPH pump can use a much smaller hose, and will have less backflush than a larger pump....

This is much the same as what SlowandSteady has previously posted...but clarifies that the small maintenance pump should be mounted as the lowest in the bilge....

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post #7 of 11 Old 01-05-2011 Thread Starter
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Quote:
Originally Posted by sailingdog View Post
Generally, the best option is to have the float switches/bilge pumps mounted at different heights. The lowest one should be the 500 GPH "maintenance" pump... this one is the cheap, heavily used, easily replaced model that does most of the pumping. Then you have a much higher-capacity one mounted about an inch or two higher than this one... that does the "dewatering" for emergency situations.
That is how mine are set up now, more or less...
I mounted everything to a 3/16 piece of 1" SS flat bar. The 500 gph pump at the bottom, then the float switch for the 500gph, and then the 2000 gph above that. I can then lower the whole assembly into the Keel/bilge about 3 ft down and secure it with a wing nut on a stud I put there for that purpose.

I guess I'll just use a 3/4 hose instead of the 1 1/8 and see how it works out. Was thinking of replacing the float switch with one of those electronic switches like the Johnson Optima and might have enough room to have that side by side with the small pump.

Thanks for your thoughts on this issue...
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post #8 of 11 Old 01-05-2011
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After reading this post

After reading this post I may hold back on our bilge pump plans.
We have a Rule 2000 and the original belt driven bilge pump ( Jabsco 36600 Series Bilge Pump 8 gpm).
We just bought a new 1 ľ inch ID through hole and elbow and valve.
We have a deep bilge.
Our bilge is generaly dry.
The rule sits at the bottom of the bilge and the float sits about 6 inches higher than the bottom of the pump. This keeps it from cycling. The hose is 1 ľ as Rule says it should be 1 1/8 but I did not find a hose that size. Anyway we were about to make the original through hole bigger to accommodate the Rule 2000.
Then we were going to use an old macerator through hole for the original bilge pump.
We are installing a new through hole for the macerator as we got a new macerator and the original through hole is above the water line. Pew!
But after reading this thread:
Now I think we may just re-build the original one and keep the plumbing the way it is as it is setup for that pump. Then either make the macerator through hole bigger or just keep it the size it is (not sure what size but it is bigger than the bilge pump through hole) and run the Rule 2000 to it and have it turn on with a manual switch (by us) if the bilge alarm goes off.
We could put a big loop in it as it not 12 inches above the water line. Says Rule.
Rule also says no check valve.



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post #9 of 11 Old 01-05-2011
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Originally Posted by SlowButSteady View Post
I don't think the back pressure really matters. As far as the pump is concerned, any back pressure from a smaller outlet is just like having it mounted so that it had to pump against a relatively large head.
Actually back pressure is just about EVERYTHING when it comes to small centrifugal bilge pumps! The flow falls off so fast with any back pressure that you wouldn't believe it. It is not unusual to get less than 25% of the rated flow just because of restrictions in the discharge piping.

Gary H. Lucas
Working as waste water system designer reading pump curves and picking pumps all the time, and I still screw it up now and then!
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post #10 of 11 Old 01-05-2011
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Quote:
Originally Posted by GaryHLucas View Post
Actually back pressure is just about EVERYTHING when it comes to small centrifugal bilge pumps! The flow falls off so fast with any back pressure that you wouldn't believe it. It is not unusual to get less than 25% of the rated flow just because of restrictions in the discharge piping.

Gary H. Lucas
Working as waste water system designer reading pump curves and picking pumps all the time, and I still screw it up now and then!
My point was that the flow rate may be lowered, but the pump shouldn't be otherwise effected. As long as there is some flow, the bearings of the pump itself will be fine. And, since these pumps get used on the order of a few minutes per month, or less, doubling, tripling, or quadrupling the run time per cycle is trivial.

BTW, as I mentioned in another recent bilge pump thread, it's a good idea to install a cycle counter on your automatic bilge pump circuit to keep track of how often it has to cycle.
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