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Discussion Starter · #1 ·
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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Telstar 28
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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... :)

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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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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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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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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gc1111 has it right....

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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Telstar 28
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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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Discussion Starter · #9 ·
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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A hose filled with water can prevent the pump from priming and pumping properly.
Thanks, Dog....You learn something every day.

Because I have no room for a vented loop and I sometimes forget to close the bilge pump valve when on a stbd tack (seacock is inches above the waterline on the port side), I installed a check valve. The bronze check valve works well in terms of preventing the back flow that cycles the pump. But with one problem solved another cropped up -- quite often the Rule pump won't push water unless I grab the hose and give the pump a hard shake or two. Once it primes, it pushes water out in a big hurry. Now I know why!!

I normally don't use the electric pump -- just when the bilge gets full and I need to clear it quickly. I do strongly recommend a bilge alarm. When it goes off I know something is amiss.
 

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FWIW - A couple of points on check valves in bilge pump hose. That's how I was set up, but have since changed it.

First, it's not easy to get a setup that works. I found no two check valves (at least, those sold at WM) are the same. I tested them by blowing into them. Some required more pressure than my lungs could create to get air to flow. Others of the same model worked easily. I got one of the easy ones. When it works, it does what you want it to do - prevent backflow.

But here's another problem in addition to what has already been said: My bilge hasn't always been the cleanest, for various reasons. When the pump comes on, which is very rarely, the last of the water to be pumped is the dirtiest. What happens is that this sludgy water, being the last to be pumped, is what remains in the hose behind the check valve. The sludge there is (and it doesn't take much) settles and blocks the check valve, preventing it from opening when the pump next activates. Not what you want to have happen. To clear it, I had to remove the hose from the check valve and let the water run into the bilge and clean the valve.

I would test the pump periodically by activating it manually. Also periodically I would remove the hose as preventive maintenance. These measures worked to assure that the pump would be ready to work when needed. But since, I've cleaned the bilge and sealed the deck and ports better. The pump comes on maybe twice a season. I didn't have the cycling problem the OP described, but I didn't like having water in the bilge. What little I have now, I've learned to tolerate.

I like the idea of a smaller pump with a smaller hose. Thatway less will settle back and prhaps solve the OP cycling problem. Sounds like a spring project for Pokey!
 

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I had bad luck with a Rule pump and a check valve - I dont know the physics of why but it seems the Rule would develop an air lock and run but not push water.
I removed it and the Rule works fine. Have not tried a loop but like the idea of the small pump and a larger secondary pump.
 

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" A check valve might initially keep the water from draining back into the bilge, but deposits of debris and detritus from the bilge water will soon prevent the valve from sealing. Besides, a check valve in a bilge pump discharge line is a bad idea because it reduces output and introduces a real risk of blockage."

DON CASEY
THIS OLD BOAT, page 281
 

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When I setup a boat, I try to keep the bilge as dry as possible.

Having a small maintenance bilge pump helps do that. The other advantage of this type of setup is that the small maintenance pumps are relatively cheap and easy to replace—since, if the boat is setup properly and normally fairly dry, the maintenance pump will be the one getting 95% of the use... and will wear out more often than the larger dewatering pumps.
 

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All good points.

A pump should be rated at so many gpm at a stated TDH (total discharge head, which includes both pressure and velocity - why a pump that can move the water might have trouble getting a long run up to velocity); in fact, there should be a whole graph showing performance under varying conditions, know as the performance curve. Generally, folks like West Marine are stingy with this information in the catalog, but, for example, the Rule web site (http://www.rule-industries.com/files/itemdoct4721.pdf) site has the information). A pump without a TDH rating is not truly "rated."

Also be aware that by changing the hose size or using a very long hose, you can run the pumps "off the curve" and reduce it output dramatically. Centrifugal pumps are based on flow, and below a certain flow rate, their ability to develop pressure declines. This related to why the prop on a boat and a pump impellor are different.

Clearly, if you install 2 pumps (small to maintain, large to de-water) a foot valve in the smaller but none in the larger is rational. Sump check valves should be flapper valves, as a rule; a small poppet valve from Home Depot is a big mistake. They are very clog prone as they have a lot of internal structure, and they typically have relatively high opening pressures - I believe a prior poster ran into that problem. Also, remember that check valves have specific mounting rules for each type; flapper valves need to be either vertical up-flow, or horizontal with the flapper up.

The comment of water freezing in the line was very good; if you have freeze weather, no checks.
 

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Another advantage to diaphragm pumps is that they are self priming and can run dry without damage. Also, the pump strainer (water intake) can fit in spaces a bilge pump can't. Then, you can mount the pump almost anywhere (within reason). I'm installing one as a maintenance pump and I'm thinking about starting with a strainer, going to a in line filter (it comes with the pump). I could then install a check valve as it would be kept clean by the filter. However, I'm thinking it might not be necessary if the pump sucks up all the water (to the pump) and then holds it. I'm trying to figure out how to switch it so it will be automatic. I thought one of those electronic bilge switches from West Marine might be the answer. I tested one, and it requires about 21/2 to 3 inches of water before it kicks on. This is about the same as a regular float switch and won't work to keep the bilge dry for maintenance. I thought I might be able to trick it by installing the switch on it's side, but it doesn't work. I'm now thinking about putting foam on the bottom of a float switch, thereby lowering the water level which activates the pump. Since the pump can run dry, I'm also considering some sort of timer. It could run the pump for 30 seconds a day for example. Thoughts??? I'll post again with the results. BTW, I think the reason back flow check valves are not advised for primary bilge pumps is that they can clog or fail. In an emergency, you can't afford to be clearing valves (of course:eek: ).
 

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I use a shop vac to dry mine out every now and then or when on the hard I dry it out and then check it for intrusion.
 

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Some of the check valves sold at West Marine are intended to work under suction. So, they can be placed in line BEFORE a diaphragm pump, not after a typical centrifugal bilge pump. This might be why people in this thread have experienced difficulty with them. A diaphragm pump I just purchased has a valve built in, so hopefully another check valve would be redundant (if the pump sucks the hose before it dry).
 

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I have a Rule pump with a checkvalve to drain my shower sump, and I frequently have the airlock problem, where the pump runs, but nothing pumps. The fix is simple--just pull the hose apart at the outlet of the pump and let it burp, then join it again. But the presssure of the water downstram of the checkvalve makes the Rule pumps very unreliable for an unmanned installation.

I put up with it for the shower sump, but have a diaphragm pump for the bilge.
 
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