Backflow Valve in Bilge Pump Drain - Good Idea?

[zboss]

We clean our bilge out bone dry and free of stuff about once a year. Its amazing the crap that ends up in there after a season of sailing - left over ends from zip ties, coins, screws, bolts, nuts, o-rings, little pieces of wire...

We use a wet/dry vac to suck it all up and give it a good mopping with some degreaser. In the interim, I will periodically hang a magnet into the bottom to see what I can pick up.

[Dockhead]

Originally Posted by RaymondR

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.

Clogging and debris is something you find out about in a real emergency, or a practice one. When the the water gets up to levels in your bilge it does not normally reach, it flushes out tons of stuff you never imagined was there, no matter how clean you think your bilges are. If you don't believe me, just talk to anyone who has ever been through a flooding emergency. This is a really serious problem which sinks boats.

Never ever put different pumps on the same outlet. Reasons are discussed above. This is extremely bad, dangerous practice. The slightest clog or stuck check valve or blown out check valve and you have no pumps.

Manual pumps by nature are much less likely to clog. But the realistic amount of water they can shift is very small compared to a large electric one.

Sent from my D6633 using Cruisers Sailing Forum mobile app

[rwidman]

Originally Posted by zboss

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?

Documentation from one of the major bilge pump manufacturers has been posted stating that check valves should not be used. They engineered these things and know what they are talking about.

We don't need to know what clogs them we only need to know not to use them.



To answer your question - debris.

[missourisailor]

Just for clarification, the Whale Supersub Bilge pump,
Whale Marine - Products
or
http://www.whalepumps.com/marine/sit...eDatasheet.pdf
come with a discharge check valve.

No saying that I installed it, but there is at least one major manufacturer that doesn't have a problem with a discharge check valve.

[zboss]

Originally Posted by rwidman

Documentation from one of the major bilge pump manufacturers has been posted stating that check valves should not be used. They engineered these things and know what they are talking about.

We don't need to know what clogs them we only need to know not to use them.



To answer your question - debris.

My Johnson L4000 has a built in check valve so please explain that.

Also, there is nada about using an additional check valve in our manual... check it out here:

http://www.spxflow.com/en/assets/pdf...1600-L4000.pdf

[Terra Nova]

Originally Posted by missourisailor

Just for clarification, the Whale Supersub Bilge pump,
Whale Marine - Products
or
http://www.whalepumps.com/marine/sit...eDatasheet.pdf
come with a discharge check valve...

Nowhere did I see any reference to this "extra" check valve coming with the pump.

[missourisailor]

Look at the second link (*.pdf file).

Middle lefthand side of first page.

Also, I can assure you that it came with one.
Looks like a tri-joker valve.

[Terra Nova]

I've looked over the linked info and cannot find any mention of this. Are you sure it isn't a spare part?

[RaymondR]

What we have here is a serious conflict of design philosophies, very common where there are numerous options.


It is quiet common in industrial settings to have a number of pumps piped into a single pipe line and it is not uncommon for each of the pumps to have a check valve on their discharges in case one of the pumps shuts down otherwise there would be back flow through the shut down pump.


My experience with check valves is that they are far more likely to get jammed open, or leak because something is caught between poppet and flap and seat, than stuck closed. In decades of experience I don't think I can remember one getting stuck closed.


My extensive experience with pumping all sorts of thick, rubbish riddled fluids on drilling rigs was that filters like the ones they put on the end of suction lines are pretty useless - they never have a large enough filter area. The next most useless are the ones you find on the suctions of submersible pumps for the same reason.


The most effective filters are the line type suction filters which generally have a large effective screen area. The best of these have bucket type screens which can be lifted out to empty the rubbish. I have seen double systems with valve manifolds which allow alternate usage so that there is no interference to production whilst cleaning screens.


The most effective systems I have seen for really trashy fluids are those set up using dewatering pumps (which use a vacuum pump to suck fluids into a chamber from which it is pumped using high volume centrifugal pumps) with paralleled large screens on the suction. One of these tandem systems had lever action dump hatches on the bottom of the filters so that the collected trash could be dumped into trash hoppers rather than lift out baskets.


My DIY sea water strainer is cylindrical, 8" in diameter, and 4" deep. It has a 2" inlet and in 20 odd years of coastal cruising has never plugged. Big inlet, big strainer area. It has a 1/2" clear polycarbonate lid fastened down with 5/16" wing nuts so that I can see into it and get the lid off quickly. Never had to do it. Massive overkill works.


The point of the above - you can pump masses of trashy fluids if you either remove the trash before it gets into the pump or you use an open impeller style pump and large discharge lines. Any valves you use with the second option should be the full opening type which in the case of check valves would be the flapper type or the rubber duckbill types.


Dogma has no place in boat design.

[Dockhead]

Originally Posted by missourisailor

Just for clarification, the Whale Supersub Bilge pump,
Whale Marine - Products
or
http://www.whalepumps.com/marine/sit...eDatasheet.pdf
come with a discharge check valve.

No saying that I installed it, but there is at least one major manufacturer that doesn't have a problem with a discharge check valve.

I have two of those. They are small, very good, maintenance pumps. Not primary pumps. I use the non return valves in these. But never in your main pump.

[Dockhead]

Originally Posted by RaymondR

What we have here is a serious conflict of design philosophies, very common where there are numerous options.


It is quiet common in industrial settings to have a number of pumps piped into a single pipe line and it is not uncommon for each of the pumps to have a check valve on their discharges in case one of the pumps shuts down otherwise there would be back flow through the shut down pump.


My experience with check valves is that they are far more likely to get jammed open, or leak because something is caught between poppet and flap and seat, than stuck closed. In decades of experience I don't think I can remember one getting stuck closed.


My extensive experience with pumping all sorts of thick, rubbish riddled fluids on drilling rigs was that filters like the ones they put on the end of suction lines are pretty useless - they never have a large enough filter area. The next most useless are the ones you find on the suctions of submersible pumps for the same reason.


The most effective filters are the line type suction filters which generally have a large effective screen area. The best of these have bucket type screens which can be lifted out to empty the rubbish. I have seen double systems with valve manifolds which allow alternate usage so that there is no interference to production whilst cleaning screens.


The most effective systems I have seen for really trashy fluids are those set up using dewatering pumps (which use a vacuum pump to suck fluids into a chamber from which it is pumped using high volume centrifugal pumps) with paralleled large screens on the suction. One of these tandem systems had lever action dump hatches on the bottom of the filters so that the collected trash could be dumped into trash hoppers rather than lift out baskets.


My DIY sea water strainer is cylindrical, 8" in diameter, and 4" deep. It has a 2" inlet and in 20 odd years of coastal cruising has never plugged. Big inlet, big strainer area. It has a 1/2" clear polycarbonate lid fastened down with 5/16" wing nuts so that I can see into it and get the lid off quickly. Never had to do it. Massive overkill works.


The point of the above - you can pump masses of trashy fluids if you either remove the trash before it gets into the pump or you use an open impeller style pump and large discharge lines. Any valves you use with the second option should be the full opening type which in the case of check valves would be the flapper type or the rubber duckbill types.


Dogma has no place in boat design.

Your sea strainer sounds excellent

And of course -- everyone is free to design his pump system as he likes, as no law that I know of requires you to fulfill classification requirements (insurance is a different matter, however).

There are different "design philosophies" for sure. But there is good design and then there is bad design.

And I submit that it is not just bad design, but horrendously bad design, increasing risks by orders of magnitude, to pump against TWO check valves -- one which must remain open and unclogged, and one which must remain closed, in order for the pump to work -- just so that you can avoid installing a second outlet.

This "design philosophy" is so bad, that it is forbidden by all classification rules which I know of, for bilge pumps.

For drill rigs or industrial processes is one thing -- never heard of a factory sinking. But for boats -- it's just unsuitable. That's not "dogma".


And if you sink your boat as a result of such a -- sorry, cockamamie pump configuration -- I can just about guaranty that your insurance will not pay for it.

[Dockhead]

Originally Posted by Terra Nova

I've looked over the linked info and cannot find any mention of this. Are you sure it isn't a spare part?

No, the non-return valve is there. And I actually use it in the two Supersubs I use for maintenance pumps.

It's not a big deal on the Supersub, because that has a rather fine screen on the pickup which does a pretty good job of protecting the valve.

That screen clogs instantly any volume of water has to be moved. As in, when I hose out my bilges. You have to take the debris off the screen every 5 minutes to keep it pumping. That's a trick on my boat as the main bilge is quite deep. Usually I hang in the bilge with someone holding my legs. Not something you'd want to be doing in an emergency.


As mentioned, it's a joker valve, not a flapper valve, and this is inherently more reliable. But this considerably restricts flow rate, another reason why this is not suitable for a main bilge pump.

[missourisailor]

Just my two cent's and that is all this is!

RaymondR is correct about industrial pump set ups.
Very common to have the primary and backup pumps plumed into the same discharge pipe. Only separated but a couple of isolation valves and check valves.
It is much more economical to run one 8", 12", 16", 24" or what ever size pipe, than two. And trash pumps can handle an incredible amount of debris. And still pump!

Also when a discharge check valve sticks open (most common but they do stick closed too), some of the effluent does go back to the source, but the restriction of the non operating pump (and the partially blocked open check valve), makes it so that it is not an "open pipe".

And yes, our plant "sinks" at least once a week because some dumbass operator won't do his/her job!

But as Dockhead pointed out, our plant is not a boat. When we flood, all we have to do to be safe, is go outside. Not quite so on a boat.

I can fully understand wanting to save precious space and time by only routing one hose. But really, is your and yours lives really worth that little amount of space and/or time?

Also, the argument about not having an available thru hull for the discharge is, IMO, hog wash!
It takes all of 5 min's to bore a 1 1/4"~2" hole in the transom of a glass boat. And another 5 to 10 min's to prep the area, bed the thru hull and tighten the nut. Most of the time you don't even need a second person. And best of all, you can do it with the boat in the water.

True you'll need two lengths of hose...but bilge pump hose is pretty cheap.

IMO...I really think that it is penny wise and dollar foolish to run two pumps, to one hose...on a boat at least.

[Gone2long]

Originally Posted by Tikka

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 am pretty sure that "air lock" was the problem.

In any case, once I cleared the line for a second time, I have not had any problems. The problem, once I installed the manual pump, may be that I ran it when there was only minimal water in the line and I forced to much air into the line, as a result.

Regards,

G2L

[Gone2long]

Originally Posted by zboss

We clean our bilge out bone dry and free of stuff about once a year. Its amazing the crap that ends up in there after a season of sailing - left over ends from zip ties, coins, screws, bolts, nuts, o-rings, little pieces of wire...

We use a wet/dry vac to suck it all up and give it a good mopping with some degreaser. In the interim, I will periodically hang a magnet into the bottom to see what I can pick up.

Shoot, I been doin' all that stuff about once a month : )

Magnet's a great idea, me thinks.

G2L