Backflow Valve in Bilge Pump Drain - Good Idea?

[rwidman]

Originally Posted by SaltyMetals

You could be right about "when" but there is also the manual bilge pump, .............. .

You should install a second float switch a bit higher than the first and rig it to send you a text message so you can rush down to the boat and use that manual pump.

The information Maine Sail posted from Rule is a good read. When the manufacturer recommends no check valve, it's probably a good idea to follow their advice.

[Dockhead]

Originally Posted by 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...




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.

A bit of thread drift --

Do you think the discharge line loop needs to be vented, or not?

[Maine Sail]

Originally Posted by Dockhead

A bit of thread drift --

Do you think the discharge line loop needs to be vented, or not?

If the discharge can ever dip below max heeled waterline then yes because it can start a back-siphon.. If always above waterline no need for one..

[pcmm]

One thing that the OP mentioned that concerns me more than the check valve is that their install goes over a beam for the engine mounts before exiting the boat, seems to indicate to me that 1) the bilge pump probably exits near the waterline which is dangerous! and 2) there isn't much of a loop to prevent water from back flowing in in the event that the boat is sitting low in the water. fix that first. bilge pumps should exit the boat near the shear line not the waterline!

[Terra Nova]

Originally Posted by RaymondR

...The reason I will install a check valve is that the large submersible pump shares a large diameter discharge with the manual bilge pump...

Huge no-no's! NEVER share bilge pump lines.

NEVER install a check valve in a bilge pump line.

[leftbrainstuff]

Originally Posted by Gone2long

I have a Rule, Model 24, 360 GPH bilge pump, with a 3/4" exit tube that I connected to a brass backflow valve using a two inch length of garden hose. The other end of the backflow valve is connected to a 1" drain hose which leads to a through hole above the waterline - perhaps two feet above the pump.

I recently replaced the pump, and reading the instructions, I noticed that they seemed to suggest that there should be no backflow valve in the line. Does anyone know why this is, and if having the valve in the drain line could cause me problems.

Also, the seems to be clogging rather frequently, but I will address that issue in a separate post.

Thanks to all for your help.

G2L

Its preferable to not have restrictions in your bilge pump circuit. Especially for centrifugal pumps which cannot pump against suction or discharge pressure drops.

However if you have the potential for backflow or reverse flow siphoning through the bilge pump outlet then a backflow preventer will be needed.

Correctly routed siphon break on the bilge pump outlet to the hull mounted outlet will usually not require a backflow preventer.

It's tricky to fit suction screens to bulge pumps. Better to minimise the chance of crap entering the bilge in the first place.

I would also not relay on a single float switch activated bilge pump. We have four, an audible high water alarm and a float switch per bilge pump. The fifth bilge pump is a manual diaphragm type.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[Gone2long]

Originally Posted by RaymondR

Depending on where you have the check valve(backflow valve) it may prevent the pump from priming and this rather than blockages might be the reason it does not always work. It's better if the water remaining in the line drains completely back into the bilge to ensure there are no airlocks trapped in it when the pump restarts. Run a loop all the way up under the deck and remove the backflow valve and see if that fixes your problem.

I thought about that, but the original pump ran for more than a year without clogging, so that is why the situation is a bit confusing. In fact, I replaced it because I thought it was failing, but after later testing, found out that it was OK, and the problem was some aspect of the way the drain was set up. That, or millions of shrimp - see my related post - "Shrimp Fry Clogging My Bilge Drain"

Thanks,

G2L

[Gone2long]

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.

You know, this makes sense to me. My original pump was discharging back into the bilge quite a bit of water. It wouldn't immediately re-cycle, but it would do so frequently. That is why I added the backflow valve.


Also, the backflow valve I have seems to have a bleeder on the top, for such purposes, and, after reading this, I think I know why I am getting the "fizzing" or hissing sound in the line, when I start taking it apart. Got a feeling that this is trapped air, and a partial vacuum or air block. Will check to see if it actually is a bleeder


Thanks a lot,


G2L

[Gone2long]

Originally Posted by rwidman

No check valve in the bilge pump discharge hose, no garden hose and no "brass" in anything that involves seawater.

Get rid of the check valve and garden hose and do it right.

That's exactly what I am trying to figure out, "What, exactly would be the right". One should also understand that I am in a 3rd world country, which is why I am using garden hose.

Keep talkin' to me. I appreciate the "do it right" perspective, though I can't always implement it.

G2L

[Gone2long]

Originally Posted by Rough Magic

Ditto on the removal of the check valve. But try switching to smooth wall hose. All the coreggations in the standard bilge hose slows down the flow, and can fill with debris. That tip came from a guy that builds boats for a living, and worked for me.

Makes sense. Thanks.

G2L

[Gone2long]

Originally Posted by sammyo

I was thinking of adding a small extra pump just for the last inch or so that would be on a separate on demand when I wanted to fully dry out that last annoying bit without leaning stretching way down with a sponge.

Yeah, I DEFINITELY know the feeling : )

Fair winds,

G2L

[Gone2long]

This thread is starting to sound like one on guns or anchoring : ) Guess I'm good at starting controversies. : )


Thanks for your input,


G2L

[Gone2long]

Originally Posted by 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.

Thank you,

Moving the check valve won't work with my setup, but it certainly helps me understand the situation. Again, this back pressure and or air seems to be causing the problem, and perhaps not clogging. There is definitely a lot of water that gets stored in the "loop" which I discussed earlier.

The line goes from the pump, 2" to the backflow valve, then over a beam which is actually about 9-10 inches high (not 6, as I previously noted). On the other side is an unavoidable loop dropping the hose down a bit, but where is used to drop the full ten inches, I have elevated it so there is less loop in the line. This seems to have helped, at least for the short term.

Thanks again,

G2L

[Gone2long]

Originally Posted by rwidman

You should install a second float switch a bit higher than the first and rig it to send you a text message so you can rush down to the boat and use that manual pump.

The information Maine Sail posted from Rule is a good read. When the manufacturer recommends no check valve, it's probably a good idea to follow their advice.

My situation is much simpler than most of those noted on this thread. The replacement pump is actually "manual" in that I must switch it on (12v). I chose the manual replacement because I got tired of hearing my automatic pump turn on and off. As noted up the thread, I have already shortened and straightened the line (did most of that before writing this thread).

I could also take out the backflow, as suggested, and will ponder that idea further. Have two real MANUAL (hand driven) pumps that handle 1 1/2 inch hose, if I ever need them. The bilge pump only handles water coming in from the packing on the drive shaft, and there is actually very little.

Thanks for your insights,

G2L

[Dockhead]

Originally Posted by Gone2long

This thread is starting to sound like one on guns or anchoring : ) Guess I'm good at starting controversies. : )


Thanks for your input,


G2L

Actually, there is practically ZERO controversy on this thread, for once Just about a perfect consensus, a rare thing on here

How to "do it right" --

* Two new holes in the boat for two new and completely separate discharges. Separate all bilge pump discharges.

* Buy a diaphragm pump for maintenance, put in a check valve in that one. Mount it lower, as low as possible.

* Mount the bigger pump higher so it won't run unless something overwhelms the diaphragm pump. No check valve.

* Loops in every discharge line high enough to eliminate any chance of siphoning.

AND . . . . . .

Bob's your mother's brother.

It's not actually rocket science.

Good luck and let us know how you get on.