Backflow Valve in Bilge Pump Drain - Good Idea?

[RaymondR]

Originally Posted by Dockhead

The easy solution to this is multiple pumps. I have a Whale Supersub as a maintenance pump. It came standard with a check valve. It has a decent strainer and has not clogged so far.

For shifting water - which is a different job, requiring a different tool, than keeping the bilge dry --, I have a pair of the large Rule 4000s. No check valves for all the reasons stated above.

Nothing wrong with a check valve provided it's not in the main pump.

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I have two separate bilges with a overflow between them. The smaller one has a small submersible pump with a 3/4" discharge back through the transom. The larger bilge has a 1 1/4" pump also with a discharge back through the transom.

At the moment I am converting the engine cooling system from raw water to keel cooled and have flushed the keel cooling tubes and hoses and dumped a lot of water into the bilge.

The large pump has been installed for a number of years and was put in for high volume water removal however it has never been used to as normally the smaller system keeps the bilge clear.

I heard the large pump cycling and found that there is sufficient volume in the large and fairly long discharge line to refill the bilge sufficiently to trigger the float switch. The pump starts, bilge empties. pump stops, backflow - starting the cycle again. Obviously the system needs a check (backflow) valve just after the pump to stop the cycling.

I will install the valve and drill a small air bleed hole between the pump discharge and the valve to bleed away any air locks.

[Terra Nova]

Originally Posted by RaymondR

...Obviously the system needs a check (backflow) valve...

Wrong conclusion.

NEVER install a check valve in a bilge pump line.

The correct conclusion is that the bilge pump system was amateur-installed. Likely the float switch is mounted too low. And the pump is likely a centrifugal that is not designed to dry the bilge. Also the outlet line probably doesn't have a vented loop at its high point, which also probably isn't close above the pump.

Don't view check valves as magic Band-Aids to fix crappy bilge pump systems.

[Dockhead]

Originally Posted by RaymondR

I have two separate bilges with a overflow between them. The smaller one has a small submersible pump with a 3/4" discharge back through the transom. The larger bilge has a 1 1/4" pump also with a discharge back through the transom.

At the moment I am converting the engine cooling system from raw water to keel cooled and have flushed the keel cooling tubes and hoses and dumped a lot of water into the bilge.

The large pump has been installed for a number of years and was put in for high volume water removal however it has never been used to as normally the smaller system keeps the bilge clear.

I heard the large pump cycling and found that there is sufficient volume in the large and fairly long discharge line to refill the bilge sufficiently to trigger the float switch. The pump starts, bilge empties. pump stops, backflow - starting the cycle again. Obviously the system needs a check (backflow) valve just after the pump to stop the cycling.

I will install the valve and drill a small air bleed hole between the pump discharge and the valve to bleed away any air locks.

I killed a set of batteries via this phenomenon.

Don't install a check valve. Install the large pump a good bit HIGHER in the bilge (mines a good 20cm higher). Then the small pump (with check valve if you like) will deal with anything regurgitated by the big pump.

But the big pump will never operate, anyway, except when you test it.

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[a64pilot]

And on the big pump wire a buzzer in so that if that pump comes on, the alarm will sound telling you somethings wrong.
Real simple to do and can be any 12V buzzer.


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[Captndave1]

A check valve at the pump holds all the water in the line all the way to the thru hull. This creates enough back pressure that the pump cannot overpower it, therefore appearing to be a blockage. One solution is to install the check valve halfway between the pump and the thru hull.

[Dockhead]

Originally Posted by a64pilot

And on the big pump wire a buzzer in so that if that pump comes on, the alarm will sound telling you somethings wrong.
Real simple to do and can be any 12V buzzer.

Exactly!

[TheThunderbird]

Bilge Pump 800W
Minor sump pump, floating switch
Portable 220V 600W pump
Additional 12V pump, with T-valve reaching different bilges

Under tension also when batteries are off.

Fishermen have engine-driven mechanical pump, but almost impossible to install it on a cruiser

[CaptainMurph]

There are plenty of ways to skin a cat, but this setup seems to have lots of merit:

1. Install a larger (2,000-4000 gpm) pump higher in the bilge and make this manual (switch controlled only)
2. Install a smaller 360-800 gpm pump as low as possible in the bilge and make this automatic (auto switch on pump or separate float switch).
3. Reduce the output hose on this pump from the nominal 3/4 to 1/2 or even 3/8".

This setup will keep the bilge as dry as location allows and the drainback when it shuts off is reduced in volume considerably due to the small output hose. Since this lower, automatic pump is mostly to remove the moisture that makes it way in through the packing gland or rain, it doesn't need to have a high capacity.

Ideally, having a manual pump with pickup down low is also a good idea.

[hsi88]

The backflow valve I bought (for admittedly a smaller bilge pump) is clear plastic. I can easily see if there is a blockage. Will be installing it on the first warm and sunny day. I like the idea of an alarm as well. Those too are inexpensive. Cheap insurance!

[RaymondR]

Originally Posted by Dockhead

I killed a set of batteries via this phenomenon.

Don't install a check valve. Install the large pump a good bit HIGHER in the bilge (mines a good 20cm higher). Then the small pump (with check valve if you like) will deal with anything regurgitated by the big pump.

But the big pump will never operate, anyway, except when you test it.

Sent from my D6633 using Cruisers Sailing Forum mobile app

The high volume pump has been installed in the larger bilge for about four years and last evening is the first time it has ever pumped water from it. The reason it pumped was that I had dumped a large volume of fresh water into the bilge fast enough for it to flow from the small bilge through the high level overflow into the large bilge.

The reason I will install a check valve is that the large submersible pump shares a large diameter discharge with the manual bilge pump (It's about a half gallon a stroke monster diaphragm pump so needs a big discharge line) Since the pump rarely cycles and has a good suction filter clogging should not be a problem.

Without a check valve I have to fiddle with the manual isolation valves otherwise when I use the manual pump it flows back through the submersible.

I would prefer not to have a check valve in the line but running another large diameter line all the way back to the transom or raising the pump would not fix the problem.

The problem is that the volume of the discharge/surface area of the bilge ratio is too small.

Like a lot of things on boats it's a conflict between the perfect and the practical.

[SaltyMetals]

You could be right about "when" but there is also the manual bilge pump, plus the bilge has a substantial wall about 6" high around the top edge to stop rubbish. The boat is very clean so i don't even get bits stopped by the wire mesh wall. I am going to give it a go in its current setup but there is nothing i can do about length of hose from the bilge to the pump. it is what it is (3 metres).

[Blue Stocking]

FYI, Stainless steel mesh for strum boxes and filtering is often available as frying pan grease shields in most large stores. Cut out what you need. The open area of most 14 x 14 mesh is about 42 % per sq. inch.. Laced mine together with Monel safety wire. therefore no blockage of the check valve.

[Dockhead]

Originally Posted by RaymondR

The high volume pump has been installed in the larger bilge for about four years and last evening is the first time it has ever pumped water from it. The reason it pumped was that I had dumped a large volume of fresh water into the bilge fast enough for it to flow from the small bilge through the high level overflow into the large bilge.

The reason I will install a check valve is that the large submersible pump shares a large diameter discharge with the manual bilge pump (It's about a half gallon a stroke monster diaphragm pump so needs a big discharge line) Since the pump rarely cycles and has a good suction filter clogging should not be a problem.

Without a check valve I have to fiddle with the manual isolation valves otherwise when I use the manual pump it flows back through the submersible.

I would prefer not to have a check valve in the line but running another large diameter line all the way back to the transom or raising the pump would not fix the problem.

The problem is that the volume of the discharge/surface area of the bilge ratio is too small.

Like a lot of things on boats it's a conflict between the perfect and the practical.

It's your boat, of course, so you'll decide, but for what it's worth I would say:

1. Sharing a discharge outlet between two pumps is a compromise too far. I would never, ever do it under any circumstances. There are just too many things to go wrong with that, and many people will tell you it's just dangerous. It's certainly against all the classification rules. For one thing, a pump with a shared discharge won't function if the check valve on the other pump fails -- the water will just get pumped into the other bilge. Are you really willing to bet your boat on a failure prone little check valve? If I were you, I would suck it up and add another outlet (or two), as a matter of priority. I added TWO on my boat. A bilge pump can discharge through topsides amidships, not necessarily through the transom. It can't be that hard, certainly not hard enough to be worth risking a sinking.

2. You need two bilge pumps in your big bilge, one maintenance and one power pump, each with its own discharge outlet. The fact that you have an overflow bilge doesn't change that (it merely complicates bilge management, actually). You can put a check valve in the maintenance pump line but not in the power pump line. If you want a really dry bilge (impossible on my boat with large diameter keel-stepped mast -- the rain pours in), you can use a diaphragm pump with remote pickup.

[Maine Sail]

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...

Originally Posted by Rule Pumps Tech Support

Both Rule and our competitors' centrifugal style bilge pumps have very little air vacuum pressure because there is a large gap between the centrifugal impeller and the impeller housing (depending on the pump, it could range between 1/16"-3/16") which allows high flow and some bilge debris to flow past the impeller without damaging the unit.

The negative side of having the large gap between the housing and the impeller is the impeller needs to come in contact with water to pull the water out of the bilge (water being a lot thicker than air).

A check valve in the bilge hose seals air in the hose and will not allow the water to come in contact with the impeller. The pump may be in a few inches of water (or completely submerged) but because of the air pocket, the pump cannot remove the water from the bilge.

If you wanted to remove as much water as possible, you could try installing a diaphragm style pump. The diaphragm pumps have internal check valves and are self priming to at least 6'. The only drawback is that the diaphragm pumps do not have as much flow as the centrifugal pumps. If you mounted the centrifugal pump switch higher than the switch for the diaphragm pump, the diaphragm pump could be used for the daily water seepage and the centrifugal pump could be used for emergency pumping.

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.

[rwidman]

Originally Posted by hsi88

The backflow valve I bought (for admittedly a smaller bilge pump) is clear plastic. I can easily see if there is a blockage. Will be installing it on the first warm and sunny day. I like the idea of an alarm as well. Those too are inexpensive. Cheap insurance!

Read my post #15 if you didn't read it and read it again if you did. Several people here have given you very good reasons why you should not install a check valve in your bilge pump output. Your "solution" of a clear plastic valve is not really a solution.

For anyone who insists on installing a check valve in the bilge pump output, I suggest installing a second bilge pump and discharge with a second float switch slightly above the first. That way, when the check valve fails and blocks the output of the first pump, the second will take over and keep your boat from sinking.