Bilge Pump Non-Return Valve

[Dockhead]

I installed a couple of Rule 4000 bilge pumps last year in my boat to supplement the ones the boat came with. The installation was fairly involved since these big pumps need big hoses and their own through-hulls.

The manual says under no circumstances to install a non-return valve in the line.

But when these pumps come on automatically (Ultra Junior float switches), the large diameter hose retains a lot of water. When the pump switches off, this water goes back into the bilge. Then the pump switches back on. And so forth.

I am no longer on shore power and I'm worried that this endless loop might drain my batteries when I am not on board.

What to do, other than install a non-return valve??!!

[noelex 77]

Non return valves have a high failure rate and provide restriction to outflow, so try to avoid them.
The best practice is to install a small pump low down that will clear out most water and mount the larger capacity pump higher for emergency use.
As an alternative some bilge pump switches, particularly the electronic kind have a separate start pumping and stop pumping points.

[simonmd]

Id say that if your worried about your bilge pumps draining the batteries, you have more important things to worry about.

[doug86]

A check valve in a bilge pump line is not only a bad idea, it could be just the loophole an insurance company is looking for to deny a claim should your boat sink suffer flooding damage.

The previous idea of a smaller pump to finish drying the bilge is the best idea. A Rule 500 would be perfect.

[smurphny]

You probably have a small volume area in which the pump sits. The switch(es) need to be set higher so that the amount of water in the hoses is not enough to refill the area where they sit. There really is no way to eliminate all the water unless you do it by hand. I suspended a "Water Witch" electronic switch on a piece of adjustable s.s. flat stock. This made it possible to get the height just right but some water always remains from the backflow out of the long discharge hoses. If internally switched pumps are placed in a small sump area as in a lot of sailboats they will cycle too much.

The backflow preventers do not seal tight enough, in any case, to stop water from flowing back eventually.

[Dockhead]

Originally Posted by simonmd

Id say that if your worried about your bilge pumps draining the batteries, you have more important things to worry about.

I have a dripless shaft seal and very dry bilges. The problem is not the volume of water coming in, but the hysteresis loop which results from the pump switching back on when a large-diameter hose full of water drains back into the bilge when the pump switches off. See:

"Another arrangement that leads to early pump failure
is one where the hysteresis loop as shown in Figure 1 is
compressed, so that only a small difference in water level
causes the pump to turn on and off. With too small a
difference, a boat with a deep bilge may have a large
amount of water contained in a long discharge hose
rising to the through-hull. When the pump shuts off, this
water can empty from the hose back into the bilge due to
gravity. This additional bilge water can once again activate
the bilge pump, causing an almost continuous cycling

of the pump."

http://www.practical-sailor.com/news...hysteresis.pdf

[bob_77903]

I also have the same situation that you do. I installed a small diaphragm pump that will pump the bilge dry. No water returns down its output hose when its shut off. It is only to pump the bilge dry, and not for safety. The bigger rules (centrifugal) are mounted higher in the bilge so that they will only come on in a case of the bilge taking on alot of water. When my bilge takes in a few gallons of water from rain, or heavy seas, whatever the case, I just turn the diaphragm pump on for a minute or so, and dry bilge

[simonmd]

In that case, adjust the float switch so that any water running back into the bilge doesn't trigger it again. As most pumps like this work on the impellor principal, they are incapable of completely pumping them dry completely, only a proper suction pump can do that.

[Dockhead]

Originally Posted by simonmd

In that case, adjust the float switch so that any water running back into the bilge doesn't trigger it again. As most pumps like this work on the impellor principal, they are incapable of completely pumping them dry completely, only a proper suction pump can do that.

Can't adjust this kind of float valve. It comes on at 2 1/2" above the bottom of it, and goes off again at 1 1/4". Apparently the water in the hose (2" in diameter) is enough to bring the level back up that 1 1/4". Raising the float switch wouldn't help since the bilge sides are vertical -- the same volume of water will raise the water level by the same amount, no matter where in the bilge this action takes place.

I think the solution is going to be to mount a diaphragm pump or a Whale Supersub as a maintenance pump, as others have suggested. Both of these variants will not return water into the bilge (the Supersub has a check valve; diaphragm pumps by their nature). And raise the big Rules up so that they only come on in case the water has gotten up above what the maintenance pump can handle.

Anybody have an opinion on diaphragm pumps versus the Supersub? I am inclined toward the latter, since it pumps much more (1100 gallons per hour nominally) and is much cheaper. Any reason why the much more expensive diaphragm pump would be worth the money? The new Supersubs are logic controlled, too -- looks like a nice unit perfect for this purpose. I would put one of them in place of the small original bilge pump.

[Capn Morgan]

Originally Posted by Dockhead

Can't adjust this kind of float valve. It comes on at 2 1/2" above the bottom of it, and goes off again at 1 1/4". Apparently the water in the hose (2" in diameter) is enough to bring the level back up that 1 1/4". Raising the float switch wouldn't help since the bilge sides are vertical -- the same volume of water will raise the water level by the same amount, no matter where in the bilge this action takes place.

I think the solution is going to be to mount a diaphragm pump or a Whale Supersub as a maintenance pump, as others have suggested. Both of these variants will not return water into the bilge (the Supersub has a check valve; diaphragm pumps by their nature). And raise the big Rules up so that they only come on in case the water has gotten up above what the maintenance pump can handle.

Anybody have an opinion on diaphragm pumps versus the Supersub? I am inclined toward the latter, since it pumps much more (1100 gallons per hour nominally) and is much cheaper. Any reason why the much more expensive diaphragm pump would be worth the money? The new Supersubs are logic controlled, too -- looks like a nice unit perfect for this purpose. I would put one of them in place of the small original bilge pump.

Hi DH

I have a Supersub smart 650 doing this job and it works a treat for maintenance. The 1100 has a non return valve included. Still, a NRV, it can get jammed open or closed. I believe the diaphragm ones practically dry the bilge and suck just about any debris you throw at them (or so they say) but tend to be of lower capacity.

[swagman]

One usually does not place a non return valve in the output line when you fit a pump that is triggered by a pressure sensor - as opposed to a float switch.
Most modern pumps tend to be triggered by a pressure sensor which is supposed to detect water as resistance in the pipe. Inserting a non return valve in the the pipe may lead to the sensor assuming it's resistance is water - and then it will recycle your pump and drain power with zero water on board.

IMHO best option if you've this kind of pump and a long pipe run above is to insert the one way valve to keep a dry bilge - just remove the auto pump option - meaning you can only use the pump in manual switch mode.

If you've one of the pumps activated by a float switch - then personally I'd not hesitate to put a one way valve in the pipe directly above a bilge mounted pump.

And I'd respectfully suggest you forget the scary insurance stories. Anyone ever seen insurance policy wording making it madatory to have automatic bilge pumping...........not me!

Cheers

JOHN

[westsail42]

While I generally don't like non return valves (in almost any application), if you install one for the bilge pump, you can help avoid debris from getting sucked up by fashioning some sort of removable "strainer cage" around the centrifugal pump. Something made out of stainless screen. This at least would help avoid large-ish debris from getting sucked up.

I do have a large cap Rule 3800 centrifugal pump with a NRV, but it is installed in a small walled off compartment in one of the two low points in the bilge. The large number of limber holes draining into this compartment have screens covering them to keep debris out. There is a lower 500GPH pump to help keep things dry.

Mind you, this is a 'crash' pump, that should only come on unless I experience a size-able hole, which should be NEVER. So it will not get regular use (except for testing and inspection where it will get cleaned as well).

As for the other low point in the bilge, as it is not easily accessible, it will have a large capacity inline diaphragm pump, in an easy access location, with a large area strainer as the pickup. Probably a smaller "keep it dry" pump too.

[ggray]

Last winter I installed the big (really big) pump plus little pump system, both with check valves just above the pumps, to replace the original mid size pump, which also had a check valve. Location where hoses can best be run has insufficient height above waterline to allow for a vented loop, hence the original use of the check valve.

However, I have experienced (once anyway) an airlock that prevented the little pump from working. It just sat there spinning without pumping. I assume there was just that tall column of water sitting above a pocket of air in the vicinity of the impeller, but that still doesn't seem like it would incapacitate the pump. Trying to decide what to do next. Probably raise the check valve closer to the thruhull.

Regardless, I think this is one of the objections to check valves in bilge pump hoses.

[David M]

Don't use a check valve to keep all that water from coming back, they can stick. Install a very small scraper pump to rid the bilge of the water that does flow back. Yes, you will have to install an appropriately sized small hose and discharge port. Never feed two or more pumps into a common discharge port.

[Blue Stocking]

I'llstart by saying that I don't like submersible pumps, and wouldn't have one on a boat. I don't believe in having the very thing which is supposed to stop your boat from sinking, submerged in the stuff which is trying to sink you, at the moment it decides to pack up and stop pumping. I am a belt driven, accessable for quick servicing, pump installer.
I make my own large filters out of stepped up PVC Ts with threaded caps to access the strainers that I roll out of Monel screen wire.
Having gotten that off my chest, I opine as follows.
Most (if not All) submersible , centrifugal pumps are sold, rated with a "no head" rating, and actually deliver far less than the advertised gph, if subjected to a lift of 6-7ft. Also the wear on the plastic stripping edge of the pump's volute rapidly reduces the pump efficiency further.
I tested my 1" ITT jabsco bilge pump wit a 7ft lift (by boat's set-up), both with and without a gravity clapper type non-return in a 1 1/4" suction PVC pick-up.
There was very little measurable difference in delivery.
Fire away folks!!