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post #21 of 51 Old 11-14-2012 Thread Starter
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Re: Bilge pump non return valve.

Lots of information here. The factory manual bilge exits out the stern. I installed the automatic electric bilge and placed the discharge high in the cockpit so I could see if there was a problem causing the pump to run. If water gets in the discharge hose I have much bigger issues. I test it occasionally to insure it works properly. During a test is when I discovered that the check valve was malfunctioning.
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Re: Bilge pump non return valve.

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Originally Posted by MastUndSchotbruch View Post
Of course you are entirely right, as far as boats and bilges are concerned.

I know I may be a bit off-topic here, this being sailnet, but as I mentioned, my application is not on a boat. I need to pump some water uphill but in my case there is no possibility that a siphoning situation develops. My problem is only that the hose is long, and the water that runs back will cycle the pump again. If I can prevent the hose emptying (or at least slow it down significantly), that will solve the cycling problem.

Seems to me that for my particular situation, a check valve close to the top end might solve the problem. Glad I read this thread, I never had thought about it.
Mast, you should install a check valve at or close to the pump. This is the kind of application I mentioned in my earlier post. This is a typical sump pump installation. This one threads directly into the outlet of a Little Gian sump pump:

Another very common example is a condensation pump on an air handler in a location that has no path for a gravity drain line.

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Re: Bilge pump non return valve.

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Mast, you should install a check valve at or close to the pump. This is the kind of application I mentioned in my earlier post. This is a typical sump pump installation. This one threads directly into the outlet of a Little Gian sump pump:
Well, I tried that. And what happened is exactly what MaineSail and other have predicted: the small Rule (centrifugal) pump could not open the valve against the water column. Probably some crud played a role there too since it actually worked when I cleaned everything nicely and wiggled the flap (this is a bronze valve from West Marine, with a metal flap pivoting on a horizontal axle). But after a day or two, it was stuck and the poor little pump was just whirring away.

I am not sure if mounting it as the top of the hose will work but it seems worth a try.
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Re: Bilge pump non return valve.

Quote:
Originally Posted by MastUndSchotbruch View Post
Well, I tried that. And what happened is exactly what MaineSail and other have predicted: the small Rule (centrifugal) pump could not open the valve against the water column. Probably some crud played a role there too since it actually worked when I cleaned everything nicely and wiggled the flap (this is a bronze valve from West Marine, with a metal flap pivoting on a horizontal axle). But after a day or two, it was stuck and the poor little pump was just whirring away.

I am not sure if mounting it as the top of the hose will work but it seems worth a try.
Mast, check valves can be bad news and are usually not required.. and, personally, I wouldn't use a heavy bronze check valve with a little pump. That is simply asking for trouble.

For your application (and the information of others) the majority of check valves sold for bilge pump applications are not air tight. Installing it at the top of the hose does not stop the water in the hose flowing back into the bilge once the pump stops - nor do you necessarily want it to.

If (for some reason) you want to hold the water in the hose, you need to buy a more expensive vane or diaphragm pump - a centrifugal pump is not designed to do this.

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Re: Bilge pump non return valve.

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Mast, check valves can be bad news and are usually not required.. and, personally, I wouldn't use a heavy bronze check valve with a little pump. That is simply asking for trouble.

For your application (and the information of others) the majority of check valves sold for bilge pump applications are not air tight. Installing it at the top of the hose does not stop the water in the hose flowing back into the bilge once the pump stops - nor do you necessarily want it to.

If (for some reason) you want to hold the water in the hose, you need to buy a more expensive vane or diaphragm pump - a centrifugal pump is not designed to do this.
You may well be right. But I now have everything and I will play around with it a bit more.

In case anyone is interested, the application is to eliminate a puddle on my deck behind the house. The reason why the backflow is annoying is that the hole in which the pump (and float switch) live is pretty small. The water in the hose is enough to fill the hose up to the level where the switch is closed, leading to cycling of the pump. The check valve solves the problem perfectly but only for a day or so. Next time it rains, the puddle is back, the pump sucking empty the battery but not sucking in the puddle . It only takes a little wiggling of the valve and everything works again but I don't want to do that each time it rains.
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Re: Bilge pump non return valve.

Quote:
Originally Posted by MastUndSchotbruch View Post
You may well be right. But I now have everything and I will play around with it a bit more.

In case anyone is interested, the application is to eliminate a puddle on my deck behind the house. The reason why the backflow is annoying is that the hole in which the pump (and float switch) live is pretty small. The water in the hose is enough to fill the hose up to the level where the switch is closed, leading to cycling of the pump. The check valve solves the problem perfectly but only for a day or so. Next time it rains, the puddle is back, the pump sucking empty the battery but not sucking in the puddle . It only takes a little wiggling of the valve and everything works again but I don't want to do that each time it rains.

Here's a trick, but please don't do this on a boat. On the hose right after the pump, but just before the check valve, drill a small hole on the bottom of the hose. You may need to experiment with hole diameter. This small hole acts like a "relief" and can allow the pump to create enough pressure to open the check valve by not just sitting there spinning and cavitating. Yes it will spit some back into the puddle but not much..
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Re: Bilge pump non return valve.

I work with centrifugal pump design every day. What's missing here is our basic tool, the pump curve supplied by the manufacturer. A centrifugal pump always runs on the pump curve, for every head condition along the curve there is a corresponding flow rate. The left end of the curve is the maximum head at zero flow, called shutoff. If you look at a pump curve you'll gain a whole new appreciation for the difficulty in applying centrifugal pumps.

You can learn a whole lot about your bilge pump by putting an open hose on it and running it in a shallow pan. Start with the open end down low and watch how much flow you get. Slowly raise the open end and watch how fast the flow rate falls off. At the height water stops coming out of the hose you have reached shutoff head. Measure the flow into a bucket and draw the curve for the pump. Some pumps have relatively flat curves downward to the right. A small amount of additional head pushes the pump back on the curve to the left and flow falls off very quickly. I attached a pump curve just to show what they include, curves for different impellors, efficiency points, horsepower curves etc.

I see here talk about having a loop well above the heeled water line. The fact is you want the loop as little above the waterline as will gaurantee you won't back flood when heeled. Any more greatly reduces the flow that you can actually pump. You might notice they rate bilge pump flow at about 2 feet of head. Lifting water 3 feet can cut the flow in half or more, and you might not get any flow at 4 feet!

There is also talk about venting the loop, to prevent a back siphon. This is true, however a forward siphon from a loop well above the water line to a discharge point above the water line actually will increase the pump flow a lot. So a tall vented loop can defeat your pump as well. When you do the test above trying raising the middle of the hose way up in the air with the open end near the ground. You'll see that the pump will move a lot of water way up high as long as the siphon on the downhill side pulls the water along. Drill a tiny hole in the top of that loop and the flow will fall way off.

A really important point missed here is discharge hose size on the pump. When you have only 2 feet of head to work with you really must avoid any friction losses. So jumping a 3/4" pump discharge up to 1" or even 1-1/4" can make a big difference, especially if it must run more than a couple of feet.

The comment about a small hole in the hose right at the pump discharge is a good one. In the instructions no one reads for commercial submersible pumps there is always a statement about drilling a 1/8" hole to prevent air locking. A bubble of air forms in the pump housing and the impeller can't grab enough water to build pressure enough to push water up the pipe. In a 44 story building in Manhattan I had to pull two pumps out of 18 foot deep tanks to drill the two holes that no one thought was important because those pumps air locked all the time!
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Re: Bilge pump non return valve.

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Originally Posted by GaryHLucas View Post
I work with centrifugal pump design every day. What's missing here is our basic tool, the pump curve supplied by the manufacturer. A centrifugal pump always runs on the pump curve, for every head condition along the curve there is a corresponding flow rate. The left end of the curve is the maximum head at zero flow, called shutoff. If you look at a pump curve you'll gain a whole new appreciation for the difficulty in applying centrifugal pumps.

You can learn a whole lot about your bilge pump by putting an open hose on it and running it in a shallow pan. Start with the open end down low and watch how much flow you get. Slowly raise the open end and watch how fast the flow rate falls off. At the height water stops coming out of the hose you have reached shutoff head. Measure the flow into a bucket and draw the curve for the pump. Some pumps have relatively flat curves downward to the right. A small amount of additional head pushes the pump back on the curve to the left and flow falls off very quickly. I attached a pump curve just to show what they include, curves for different impellors, efficiency points, horsepower curves etc.

I see here talk about having a loop well above the heeled water line. The fact is you want the loop as little above the waterline as will gaurantee you won't back flood when heeled. Any more greatly reduces the flow that you can actually pump. You might notice they rate bilge pump flow at about 2 feet of head. Lifting water 3 feet can cut the flow in half or more, and you might not get any flow at 4 feet!

There is also talk about venting the loop, to prevent a back siphon. This is true, however a forward siphon from a loop well above the water line to a discharge point above the water line actually will increase the pump flow a lot. So a tall vented loop can defeat your pump as well. When you do the test above trying raising the middle of the hose way up in the air with the open end near the ground. You'll see that the pump will move a lot of water way up high as long as the siphon on the downhill side pulls the water along. Drill a tiny hole in the top of that loop and the flow will fall way off.

A really important point missed here is discharge hose size on the pump. When you have only 2 feet of head to work with you really must avoid any friction losses. So jumping a 3/4" pump discharge up to 1" or even 1-1/4" can make a big difference, especially if it must run more than a couple of feet.

The comment about a small hole in the hose right at the pump discharge is a good one. In the instructions no one reads for commercial submersible pumps there is always a statement about drilling a 1/8" hole to prevent air locking. A bubble of air forms in the pump housing and the impeller can't grab enough water to build pressure enough to push water up the pipe. In a 44 story building in Manhattan I had to pull two pumps out of 18 foot deep tanks to drill the two holes that no one thought was important because those pumps air locked all the time!
Also the voltage makes another HUGE dent in performance of these pumps. Suffice it to say that a Rule 2000 when installed in a sailboat may not even pump 25% of its face value rating... Many of these pumps are rated at "open bucket" (which means NO HEAD) and at charging voltages... Often times the little diaphragm pump with the $hitty GPH rating will outperform the centrifugal pump when "installed"...
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Re: Bilge pump non return valve.

Quote:
Originally Posted by MastUndSchotbruch View Post
Well, I tried that. And what happened is exactly what MaineSail and other have predicted: the small Rule (centrifugal) pump could not open the valve against the water column. Probably some crud played a role there too since it actually worked when I cleaned everything nicely and wiggled the flap (this is a bronze valve from West Marine, with a metal flap pivoting on a horizontal axle). But after a day or two, it was stuck and the poor little pump was just whirring away.

I am not sure if mounting it as the top of the hose will work but it seems worth a try.
Mast, when I replied to your previous post, you said your question was NOT a boat application, that you wanted to pump water uphill, and not have it flow back when the pump cycled off. You DIDN'T say you were actually using a Rule bilge pump.
The solution to your problem is to get the right pump. Note: the right pump will have a power cord that you will plug into a 120 volt receptacle. It will have sufficient head to pump the height you need to pump to and overcome the head losses from the discharge hose, turns, bends, and check valve, if used. It will likely be 1/6th hp, perhaps 1/4, impossible to say without knowing all the specifics.

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Re: Bilge pump non return valve.

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Originally Posted by Maine Sail View Post
Also the voltage makes another HUGE dent in performance of these pumps. Suffice it to say that a Rule 2000 when installed in a sailboat may not even pump 25% of its face value rating... Many of these pumps are rated at "open bucket" (which means NO HEAD) and at charging voltages... Often times the little diaphragm pump with the $hitty GPH rating will outperform the centrifugal pump when "installed"...
You are right, and rating a pump at charging voltage constitutes fraud in my book. I didn't think about the voltage when I was writing, I seldom see anything other than 480 volts 3 phase, and voltage is seldom a problem!

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