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Old 05-03-2016, 16:10   #46
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Originally Posted by Maine Sail View Post
If those of you using check valves in centrifugal pumps could only see the tens of thousands of dollars in ruined batteries or damaged cabin soles or engines etc. that I have seen as a result of improperly installed check valves you may think twice about ignoring the manufacturers advice.

In a well designed bilge system you would install a diaphragm "nuisance pump" to deal with nuisance water and let the Rule/centrifugal pump deal with oh $hit level water....

This was from the Rule Pump web site before the changeover to Xylem.

"The Rule Pumps FAQs:

Q: Can I install a check valve on the pump discharge?


A: Check valves are not recommended

Why doesn't Rule Pumps want check valve on the pump's discharge?

A: Check valves are prohibited by the American Boat & Yacht Council for use as an anti-siphon device-and with good reason: They're notorious for failing in both the open and the closed position, which respectively leads to flooding or failure to pump. If the valve is close to the pump, the pump may not be able to overcome the weight of the water on the other side of the valve, rendering the pump ineffective.

Q: Why does my automatic Rule Pump turn off if I install a check valve on the discharge of the pump?

A: The automatic bilge pump turns on about every two and a half minutes to "check" for high water. If water causes resistance on the pump, it continues to pump until the resistance lowers. With the check valve installed at the pump, it can't feel the weight of the water, and shuts off, allowing the bilge to fill with water!"



Rule does not recommend a check valve on their centrifugal pumps. You can always do what you want on your boat but you would be ignoring the advice of the manufacturer of the pump, and creating a potential safety issue. The first priority of a good bilge pump system design is to design a good system that is safe.

Just because DIY's and builders do it, to save money, does not make it a correct or necessarily safe installation.

A prudent installation on a sailboat, where you want to prevent flow-back, is to either to install a diaphragm pump, the ideal solution, or to get a float switch with a delay or install a smaller "nuisance water pump". The delay will not always solve the problem however so a diaphragm pump, that can handle a check valve, or has the check valve feature built in, is the proper & safe solution to prevent flow-back.

A check valve in a centrifugal pump is not a good solution to flow-back, it is a potentially dangerous installation.

If you want to solve the problem in the correct manner then you'll want to install a diaphragm pump. If you want to go against the sage advice of the manufacturer, by all means, use a check valve....

Other than what I posted above. Here's one of the responses Rule sends out when you ask this question. This was sent to one of my customers who chose not to believe me. He then got really angry when his cabin sole was ruined and tried to blame it on Rule sending them a rather terse letter. I had already warned him not to install the check valve but he ignored the installation instructions and my advice based on experience.. The whole shebang cost him nearly 4k for a new cabin sole...




In that last sentence Rule nails it.... That is a proper bilge pumping system which has no check valve in the centrifugal pump discharge....

If you want to prevent back-flow use a two pump system a "nuisance pump" (diaphragm) and a "emergency" pump (Centrifugal) you could even go further with engine driven oh $hit pumps too... If I had a dime for every bank of batteries a stuck check valve has murdered on a centrifugal pump......................

If you want a check valve please use a rotary vane or diaphragm pump that has the ability to deal with the head pressure of the standing water, or air locks, and to push open a sticky check valve. Most small boats can't swing the loads of a rotary vane pump so a diaphragm pump is the way to go.

Centrifugal pumps with check valves often just make neat little bubbles and the water remains in the bilge. Seen this far too many times to count and the damaged or sunk boats that go along with it..

I am the guy replacing the batteries that the bilge pump killed when the check valve stuck and the float switch remained ON.........

That said you can design a bilge pump system safely but it would not include a check valve on a centrifugal pump that is not specifically designed for one.
Thanks for all the details. Well appreciated.

G2L
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Old 05-03-2016, 16:54   #47
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

Another way to keep the bilge dry is to use a 3 pump system.....this requires a bit of explanation:

Have a small 2 gallon grey water tank with its own discharge pump (pump number 1).
Pump number 2 is a tiny pump which pumps bilge water into the grey water tank through a 1/4" hose, pump 2 has its own switch. This keeps the bilge as dry as possible since there will be very little runback through that tiny 1/4" hose. When the grey water tank water level is high enough the grey water tank pump activates, any runback goes into the grey water tank again. No check valves required.
Pump number 3 is the normal large bilge bump.
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Old 05-03-2016, 17:03   #48
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

I find it hard to believe a check valve can get stuck closed by something that is not big enough to even get into the hose in the first place. The grates on my pump are maybe 1/4" and my bilge pump hose is 2.5".

What usually clogs check valves?
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Old 05-03-2016, 18:06   #49
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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Originally Posted by Singleprop View Post
Another way to keep the bilge dry is to use a 3 pump system.....this requires a bit of explanation:

Have a small 2 gallon grey water tank with its own discharge pump (pump number 1).
Pump number 2 is a tiny pump which pumps bilge water into the grey water tank through a 1/4" hose, pump 2 has its own switch. This keeps the bilge as dry as possible since there will be very little runback through that tiny 1/4" hose. When the grey water tank water level is high enough the grey water tank pump activates, any runback goes into the grey water tank again. No check valves required.
Pump number 3 is the normal large bilge bump.
In other words, why use 2 pumps, which you can get the same results with 3? Plus a tank?

A great idea if you're convinced your systems aren't nearly complicated enough, and you're determined to do something about it!
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Old 05-03-2016, 22:59   #50
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

It makes perfect sense if you already have the grey water tanks, I have them in 3 sections of my boat. Just add the tiny pump and a switch. and feed the water to the tank. Cheap, easy and not complicated at all.
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Old 06-03-2016, 03:37   #51
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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Originally Posted by zboss View Post
I find it hard to believe a check valve can get stuck closed by something that is not big enough to even get into the hose in the first place. The grates on my pump are maybe 1/4" and my bilge pump hose is 2.5".

What usually clogs check valves?
Debris in the water (and there's always debris in bilge water, especially in a flooding situation) catches in the check valves, as that is the main restriction in the line. The debris which gets caught there, causes them to stick open, or sometimes closed, or clogs form there.

Probably the bigger they are, the less the risk. 2.5" is a pretty good sized line.
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Old 10-03-2016, 13:50   #52
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

It is very important to understand why and when the check valve is used.
1/narrow deep bilge , a check valve is a must, because amount of water drains back is enough to activate pump again.
- check valve is perfectly OK to use in any installation providing , it's always submerged to prevent air lock. The bilge pump is not capable manage air lock, and water back pressure hold it close...system would not work.
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Old 10-03-2016, 14:40   #53
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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Originally Posted by Tikka View Post
It is very important to understand why and when the check valve is used.
1/narrow deep bilge , a check valve is a must, because amount of water drains back is enough to activate pump again.
- check valve is perfectly OK to use in any installation providing , it's always submerged to prevent air lock. The bilge pump is not capable manage air lock, and water back pressure hold it close...system would not work.
Not just narrow deep bilge but also long discharge lines.

Right after the pump will minimize the amount of back flow. Probably the best way to guard against air locking is to drill a small hole in the discharge line between the pump discharge and the check valve to allow the trapped air to escape. This will return a small volume of the pumped water into the bilge but if the hole is kept fairly small the volume of water returned is of no consequence.
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Old 10-03-2016, 15:14   #54
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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Originally Posted by Tikka View Post
It is very important to understand why and when the check valve is used.
1/narrow deep bilge , a check valve is a must, because amount of water drains back is enough to activate pump again.
- check valve is perfectly OK to use in any installation providing , it's always submerged to prevent air lock. The bilge pump is not capable manage air lock, and water back pressure hold it close...system would not work.
I beg to differ. Air lock is by far not the only thing which can make a check valve fail or clog. That's one of about 10 failure modes.

Check valve is not a "must". On the contrary; it's a "don't". A separate maintenance pump is what is a must, if you have problems with bilge pump cycling. It's all explained pretty well further up in the thread.
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Old 10-03-2016, 15:33   #55
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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I beg to differ. Air lock is by far not the only thing which can make a check valve fail or clog. That's one of about 10 failure modes.

Check valve is not a "must". On the contrary; it's a "don't". A separate maintenance pump is what is a must, if you have problems with bilge pump cycling. It's all explained pretty well further up in the thread.
+1
Clear concise and simply explained.!!
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Old 10-03-2016, 22:17   #56
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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I beg to differ. Air lock is by far not the only thing which can make a check valve fail or clog. That's one of about 10 failure modes.

Check valve is not a "must". On the contrary; it's a "don't". A separate maintenance pump is what is a must, if you have problems with bilge pump cycling. It's all explained pretty well further up in the thread.
So we should remove all the manual bilge pumps as each of them generally has an inbuilt suction and discharge valve which in each case is a check valve????

The correct solution if you are concerned with debris clogging the valves in a bilge pump is to install a decent sized screen so that the debris is screened out before it has a chance to make mischief.

The only realistic solutions to the back flow induced cycling of the submersible pump are either to increase the hysteresis of the switch, which is generally not possible with off-the-shelf float style switches, so that a greater volume of flow back is acceptable or put in a check valve.
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Old 11-03-2016, 04:52   #57
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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So we should remove all the manual bilge pumps as each of them generally has an inbuilt suction and discharge valve which in each case is a check valve????

The correct solution if you are concerned with debris clogging the valves in a bilge pump is to install a decent sized screen so that the debris is screened out before it has a chance to make mischief.

The only realistic solutions to the back flow induced cycling of the submersible pump are either to increase the hysteresis of the switch, which is generally not possible with off-the-shelf float style switches, so that a greater volume of flow back is acceptable or put in a check valve.
Indeed not -- a screen fine enough to prevent clogging of a check valve will itself clog even faster. Even a normal strum box is a problem in an emergency. This is no solution at all. A pump set up like that will be useless in an emergency.

The realistic solution to back flow induced cycling is to use a maintenance pump at the bottom of the bilge, ideally a diaphragm pump, but can be a small impeller pump with a check valve. Then locate the main, water-moving pump higher up, with NO CHECK VALVE, so that it is not activated at all with normal amounts of water.

The strum box should be only as fine as necessary to prevent clogging inside the pump itself. FINE SCREENS ON BILGE PUMPS DISABLE THEM. Better yet, use a KM Bilge Predator pump which is macerating and needs no strum box at all.


Concerning manual pumps -- these are DIAPHRAGM pumps, which are quite tolerant of back pressure and relatively tolerant of imperfect priming. Unlike impeller pumps, which are very finicky. But even with this tolerance, manual bilge pumps are notorious for not working when you need them -- exactly because of the various things which can go wrong with the valves. You don't want any valves, obstructions, clogging points, or screens in that pump which you depend on to shift large volumes of water.
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Old 11-03-2016, 21:28   #58
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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Indeed not -- a screen fine enough to prevent clogging of a check valve will itself clog even faster. Even a normal strum box is a problem in an emergency. This is no solution at all. A pump set up like that will be useless in an emergency.

The realistic solution to back flow induced cycling is to use a maintenance pump at the bottom of the bilge, ideally a diaphragm pump, but can be a small impeller pump with a check valve. Then locate the main, water-moving pump higher up, with NO CHECK VALVE, so that it is not activated at all with normal amounts of water.

The strum box should be only as fine as necessary to prevent clogging inside the pump itself. FINE SCREENS ON BILGE PUMPS DISABLE THEM. Better yet, use a KM Bilge Predator pump which is macerating and needs no strum box at all.


Concerning manual pumps -- these are DIAPHRAGM pumps, which are quite tolerant of back pressure and relatively tolerant of imperfect priming. Unlike impeller pumps, which are very finicky. But even with this tolerance, manual bilge pumps are notorious for not working when you need them -- exactly because of the various things which can go wrong with the valves. You don't want any valves, obstructions, clogging points, or screens in that pump which you depend on to shift large volumes of water.
It does not need to be a fine screen. All of the submersible pumps I have used on the boat have a screen incorporated in the base. The screen mesh need be no finer than these. Using a large surface area screen of the same mesh size as on the submersible pump will assist in preventing it from clogging.

The maintenance pump is a fine solution, and my double bilge system has this arrangement but, the smaller pump has smaller inbuilt suction screening and is itself prone to plugging, and all of these pumps has to have either it's own discharge line overboard or include check valves to prevent back flowing through the non working pumps. Since I have four bilge pumps and prefer to discharge back through the transom it would require a lot of plumbing and hull penetrations. Sharing with check valves is a much more practical solution.

My manual bilge pump has 1 1/2" suction and discharge and a 10" diameter diaphragm and I am fairly confident it would pump marbles through without clogging. What do you keep in your bilge that would cause such a severe clogging problem anyway?

As I age I am tending to become more paranoid. After I put the permanently running centrifugal under the engine to hold off the next bout I intend to put a stand in the middle of the boat onto which I will put my 9.8HP dingy outboard. The propeller will blast bilge water into a fixed shroud with a 6" discharge hose back out through the transom. With all the electric bilge pumps going, the main engine pump and outboard both at full revs, and me pumping on my giant manual pump like mad, if I can't keep the boat afloat I just deserve to perish.
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Old 11-03-2016, 21:33   #59
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

Oops, I forgot the 1 1/4" 800W AC electric sump pump and 2.2kW genset I also have.
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Old 11-03-2016, 22:11   #60
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Re: Backflow Valve in Bilge Pump Drain - Good Idea?

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It is very important to understand why and when the check valve is used...
Yes, it is important to understand check valves should never be used in a bilge pump system.
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