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  #1  
Old 12-22-2008
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Bilge pump issue

Hello,
I have read quite a bit on this issue on previous threads but I'm still confused...
Here it is:
This recently purchased O'Day 30 had an electric bilge pump with no float.
So, I decided to replace with an automatic one (rule-mate 750).
The problem is regarding the backflow...
The outlet hose has to go about 4 feet up and 7 feet back on the way out.
So, when the float senses no water, the pump stops, everything in the hose makes its way back in the bilge (which is narrow, not much surface area) and the whole process obviously starts again and never ends until the battery dies.
The easy solution is to raise the pump quite a lot to be above the constant remaining water, but then I have constant remaining water, and quite a bit of it.
My thoughts were to put in a non-return valve just past the pump outlet, but some people on this board advise against that.
What is the reason why such valve is a bad idea??
And if so, what is the solution.
I read about the two pumps set up, but I don't believe that will help my problem considering the elevation issue.
Any idea?
Thanks.
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Old 12-22-2008
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Install a check valve in the hose. A loop in the hose would also help.

Defender has them in 3/4" and other sizes.

S-
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Old 12-24-2008
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What I generally recommend, if you want to do the bilge pump setup properly is the following:

First, install a small "maintenance pump" as low in the bilge as possible, using relatively small diameter hose. This pump's job is to keep the bilge relatively dry from the water that routinely gets into it—the stuff that comes down a keel-stepped mast, the water from the packing gland on the prop shaft, etc. This should have a bilge pump counter on it, so that you know how often it is kicking off... if the number of times it is kicking off per day increases dramatically, you have a problem.

The reason you want a small diameter hose for this is to reduce the amount of water that backwashes when the pump shuts down. BTW, a diaphragm pump would also work, and wouldn't backwash.

Put a loop in the drain hose for this to reduce the backwash.. the high point should be as close to the pump side and as far from the output side as possible.

Not a big fan of check valves. If it bothers you that much, get a diaphragm pump instead of an impeller one.

The next bilge pump should be a high-capacity one, with a high-water alarm, and it should be mounted an inch or two higher than the first pump. This is a dewatering pump...

Quote:
Originally Posted by JSailer View Post
Hello,
I have read quite a bit on this issue on previous threads but I'm still confused...
Here it is:
This recently purchased O'Day 30 had an electric bilge pump with no float.
So, I decided to replace with an automatic one (rule-mate 750).
The problem is regarding the backflow...
The outlet hose has to go about 4 feet up and 7 feet back on the way out.
So, when the float senses no water, the pump stops, everything in the hose makes its way back in the bilge (which is narrow, not much surface area) and the whole process obviously starts again and never ends until the battery dies.
The easy solution is to raise the pump quite a lot to be above the constant remaining water, but then I have constant remaining water, and quite a bit of it.
My thoughts were to put in a non-return valve just past the pump outlet, but some people on this board advise against that.
What is the reason why such valve is a bad idea??
And if so, what is the solution.
I read about the two pumps set up, but I don't believe that will help my problem considering the elevation issue.
Any idea?
Thanks.
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Old 12-24-2008
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SD, you advise against a check valve but you don't say why. Then you say you can use a diaphram pump as they don't need a check valve. The truth is a diaphram pump doesn't need an external check valve because there is an internal one built in. So if a check is bad on a centrifugal pump, why is one ok on a diaphram pump?

It sounds like the OP needs a float with more deadband, so that the water gets a bunch higher in the bilge before it pumps it out, and it pumps it to a lower setting. I am not sure if the floats for boats are adjustible in that way.

If it were me, I might try a checkvalve, a size bigger than the hose size if I could (1" check on a 3/4" hose). The worst that can happen would be some debris gets in there and it's stuck open.

Eric
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Old 12-24-2008
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Here's my logic for not using a check valve.

With a check valve installed near the pump, the hose will remain full of water. In my case, that will freeze in the winter and make the hose burst.

I have a Rule "automated" pump. It has an internal sensor that makes it come on when the water level rises, but it stays on for 20 seconds after the sensor is satisfied, getting out more water. In my case, this is enough to reduce the amount of backwash so it doesn't make the pump come back on.
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Old 12-24-2008
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A vented loop will minimize the backflow and insure no back siphoning. Run the pump outlet as close to straight up to the vented loop as you can to minimize the amount that flows back.
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Old 12-24-2008
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gc1111 has it right....

Quote:
A vented loop will minimize the backflow
I had the same problem and nearly sunk the boat. The PO had a large capacity Rule pump in the bilge, a check valve, and then a run of 15' to the exit at the transom. With this installation, I had a recurring problem where the pump would run, but nothing would exit the boat. We ended up draining the batteries after a tropical storm passed, the bilge filled (rainwater draining trough the mast to the bilge), and the pump ran and ran....

Investigation here on Sailnet and elsewhere led to the solution......

As sailingdog implies, centrifugal pumps pumps are high capacity, but don't have much power. When the exit hose is filled with water, there is enough backpressure that the pump can't push new water past it, so the pump just runs.

The solution is simple - install a vented loop (readily available) as close to the pump as possible and make sure that the top of the loop is the highest point in the route. In our case, this fixed the problem permanently and inexpensively. I wonder why the PO lived with this mickey mouse installation for so long.....
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As pointed out by others, most of the common bilge pumps are impeller based, and as such, don't generate much pressure. A hose filled with water can prevent the pump from priming and pumping properly. A diaphagm pump doesn't technically have a check valve, but functions as one due to the design. Also, a diaphragm pump generates a lot more pressure than does a centrifugal pump does.
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Old 12-25-2008
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Thank you for all the advice/explanation.
It looks like diaphragm valves are quite expensive.
I believe my problem is made worse by the fact that I've installed a Rule 750 with a 3/4" outlet, into a 1" hose (the existing set up), so therefore I lose some pressure and I have more backflow than desired.
I think I might try to change to a Rule 1100 which has a 1 1/8 outlet, and by going into the 1" hose I would increase the pressure a bit.
SD, as the flow capacity of the 1100 vs 750 increases, is there much difference in the pressure the 1100 puts out vs the 750?
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Jsailer—

None of the RULE bilge pumps creates much pressure. The ratings for most impeller based bilge pumps are based on zero hose resistance and zero head or lift on the output side...

Personally, for the maintenance pump, I'd go with as small a pump as possible, using the smallest diameter output hose as possible. 1/2" hose does just fine for a "maintenance" pump, since, it really doesn't require high-throughput.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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