Bilge pump back flow preventer?

[Concordia...41]

I have a Rule 1500 (well, two actually), but the primary one has always run too much for my taste because each time it pumps and turns off the water in the hose (approximately 10' run aft and then above the waterline and back down to the thru-hull) runs back down into the bilge and causes the pump to cycle again.

If the secondary one is running I have worse problems... :rolleyes:

When we first set up the system, I argued for some kind of flapper valve at the bilge pump or at a low point in the line to keep the pump from this semi-constant state of pushing water up the 7' or so run only to have it run back down and trigger the float switch all over again...

Seems like this would be a pretty common problem? :confused: Which would, by rights, have a pretty common solution. :)

Thanks!

(I'm off to the boat for a couple of hours now... :))

- Margo & Sarah

[Dave Davis]

Can you get the above the waterline part right after the discharge to the pump rather than just before the thru-hull? That way you're only dealing with a couple feet worth of water rather than the additional 10 feet.

Alternatively there are one way valves (check valves) available that you could put in the line.

http://www.nibco.com/cms.do?id=2&pId=160

http://www.connectworld.net/plast/check_valves.html

[SchoonerRat]

It may not be the absolute solution, but a check valve in the output hose should help a lot. In theory a check valve will only allow water flow in one direction; in practice I find that they usually leak a bit.

[BarnacleGrim]

A check valve would probably reduce the performance of your bilge pump. My advice is to either move the float switch further up, or get a smaller bilge pump.

[sv Lorelei]

A check valve will seriously reduce the output max gpm of the pump and introduces a component into the system that is likely to fail or clog introducing a maintenance problem. Flapper valves are somewhat better but the pump still has to work against the valve and they will also eventually clog with bilganium. I'm assuming the exit loop from the bilge is already as short as possible, but running a loop as straight as you can upward above the waterline before you head it off to the exit may be a way of reducing
the volume of backwash. Another method I've seen used is to plumb a smaller primary pump with a separate float switch and a very small line (1/4 inch or so). It won't pump you out as fast but the line diameter will seriously reduce the amount of backwash. Pump run time will be longer per cycle, but the number of cycles will probably be reduced, so energy-wise it should work out as a wash.

[CundysHarbor]

Please do not install a check valve. It will, trust me on this, eventually get stuck. If it sticks in the open position, you have no check valve. If it sticks in the closed position, you have no pump. A little water in the bilge never hurt anything.

[Ian McColgin]

First safety:

A high loop is fine so long as the through-hull remains above the waterline. As soon as it happens below the waterline and the automatic bilge pump runs one last time before the battery dies alltogether, it's the perfect siphon and down she goes. So, a high vented loop as you have in a head, is safer.

Diaphram pumps (there are automatics but they are pricier than the Rule type) essentially have two check valves built right in. Given the incredible durability of diaphram pumps, the prejudice against check valves seems hard to fathom until one realizes that all too often people get check valves at the hardware or plumbing supply joint rather than a proper marine flapper.

A proper marine check valve will be more impervious to jamming than the pump itself and add no noticable resistance to the flow. Coupled with a proper loop you about have the issue solved.

G'luck

[Concordia...41]

Thanks all.

If this (from one of the above links) is the correct gizzy do - http://www.nibco.com/assets/T480FP.pdf I'll use those specs check & the local marine supply place (or order one).

My only question is that the literature states it takes 1/2 lb of pressure to open. I guess that's not too much :confused:

OK, my break's over... back to the boat :)

[Gary E]

One measurement that the nibco site does not tell you is how much flow each check valve is capable of and how much pressure drop when at that flow rate. Wonder if they can tell you.

[sv Lorelei]

You're really more concerned with flow (gph) than pressure (psi). Generally speaking, the rule style centrifugal type pumps are generally rated at the output port pumping on the level. Every lbs of additional head reduces the output of the pump. Increasing hose size for instance will decrease total resistance per cubic inch, but the additional weight of the water will also increase the head that the pump has to overcome in order to start moving water out. The same is true with any other component you put in the system, the more resistance to flow the produce, the less efficient they're going to be. So you could conceivably have a 1500 GPH pump that would only be capable of moving 500 GPH overboard yet be working right in it's operational parameters. In positive displacement pump such as a diaphragm pump this isn't as much of a factor since backflow limitation is inherent in the designs, and the diaphragm will keep pushing until either the diaphragm or the valves fail. But the fact is there is no magic bullet that is going to be 100 percent efficient and get you 100 percent dry and be 100 percent reliable.

[SV Papillon]

I'm guessing you are using the rule float switch? I had the same problem with this type of float switch. The volume of water pumped in the switches circut is only the height of the switches swing. The float comes up and the mercury rolls back closing the circut when the float comes down the mercury rolls out and opens the switch. This is fine for a on off scenario but only gives you several inches of volume to pump in a tight bilge. If you look in sailing magazines or online there are solid state proximity switches with built in timer circuts. In my opinion the ideal setup for your primary pump is a level switch set at pump level on a timer. There are lots of different scenerios depending on the size of your bilge and the how the pump sits in it having a timer will help eliminate the short cycling by running the pump long enough so the water in the line coming back won't restart the pump. If you have a secoundary pump you can use your standard float switch set higher than the normal level you are dealing with. I have tried check valves, the only ones that will seat properly in this application are in line spring ball checks, they come in bronze or you can get white pvc ones. from most plumbing places. But unless everyone on board has alapicia they will plug with hair or any other stuff that eventually makes it to the bilge. Johnson pumps have a little rubber check flap that is part of the discharge nipple. so far so good on the one I'm using.

Jake

[Dave Davis]

I don't think the linked valve will work with your Rule 1500, but you might try this one: http://www.whalepumps.com/portable_sanitation/product_list/114/0/

Or Beckson's: http://www.jamestowndistributors.com/userportal/show_product.do?pid=13817&familyName=Beckson+In-Line+Check+Valve

Designed more to support your use.

[John B]

Where does the pump water exit the hull Margo?

[Concordia...41]

The thru-hull is about 4" above the waterline. As such, if I ever took on water and when we're on a starboard tack it is submerged. So not only does the discharge line make a turn at the highest available point above the water line, it is vented.

By design, Concordia bilge pumps discharged into the cockpit just above the cockpit drain. Theory being that made you more aware of the how often the pump was running, and if your socks got wet you obviously had a problem. SARAH's system had been changed before my tenure, and we simply ran to the same thru-hull.

Going to a simpler system is tempting, however, I'd still have this back-flow problem. There would be a couple less foot of hose height as we wouldn't have needed to get over the waterline and build in the syphon break. But there would still be a 4-5' run aft and upward.

Anyway, the thru-hull was there and now the system is in place. I just need to get a moderately efficient system to stop the back wash. Anything at this point would be a gain... :(

Some of these arguments against a flapper valve and check valve are why we didn't put one in the system to start, but while I agree that debris would cause a flapper valve to stay open, the damn thing runs nearly constantly as is, and if a piece of debris got hung in it, well, I'd be exactly no worse off than I am now. And I find the odds that a piece of debris would somehow keep the flapper valve closed to be astronomical.

As to the pump running harder with a check valve, the thing cycles roughly 12 times then quiets for a few minutes and then starts the process again. That can't be good for the pump.

As mentioned, it's the float switch kicking back on when the cup or so of water that's in the run comes back down the line as soon as the pump stops.

Edited to add that just as I've been working this through in my mind as I typed this out. I'm going to put a check valve in the primary pump's line and leave the secondary alone. That will cut down the wear and tear on the first pump and the second is always there in case of emergency. Also, I may very well go back to the cockpit drain option. I'm at least a year away from the planned rebuild / overhaul of the galley - engine box area and as those final cabinets go into place, it will be the perfect time to make changes in that area.

Thanks for the advice. You all are the best!

[Ian McColgin]

As clarification to a point in #14: Head, height of lift, is a matter of PSI and is not affected by the diameter of the hose. It takes no more or less effort in PSI to push up 4' whether the hose is 1" or 2" or 6" unless the hose diameter is too small to accomodate the pump's capacity. What is different, and in terms of backflow can make a whopping difference, is the volume of water static in the hose.

There is little benefit to making the hoses and seacocks notably larger than the pump's exit.

With diaphram pumps more than others, one can increase capacity (within limits) simply by increasing the entrance and exit ports and attendent hoses. My Edison diaphram had nearly a gallon per stroke but shoving that gallon through the 2" hose is much faster than the slightly cheaper and more common 1-1/2" units that have the same diaphram.

[John B]

I think you should put or have a non return valve at or past the siphon break and fairly close to the high point .Double clamped and fixed so that if the connection broke it would remain well high.
As to the head water issue , I think you should accept that... what , a cup or two of water.. and raise the switch slightly to accomodate it.
As I've said here before, we found this out the hard way so for us its empirical even if its only anectdotal for you :D( see bilge thread:))

On motoring to Kawau in no wind one day Kirsty decided to give the pump a run. The system and exit is like yours but no siphon break and the exit is an old exhaust skin fitting about 18 inches above the w/l.
When we nearly were at our destination Kirsty noticed the sole was swimming so I backed off the throttle and zipped down for a look. there was no leak.
What was happening was by running the pump motoring at 6.5 knots the fitting was under, when the pump was turned off it syphoned back and ran a 3/4 hose worth of water for two hours into the boat. Of course it ceased when I backed off and slowed the boat.
Maybe the syphon break would have fixed the problem but I'm not so sure I trust them either. Anyway with a break and a non return valve you get redundancy eh.

[Ian McColgin]

Depending on the shape of the bilge, raising the float switch may or may not help. The float operates of the same verticle distance - typically a couple of inches - no matter where placed. A deep bilge with nearly verticle sides takes a bit less back flow to get back to switch-on than a flatter catboat bilge with shallow wide bilge.

But really, neither should make much difference.

[Gary E]

So after you have figggerd out how to remove most of the water, here is a system that will remove ALL of the rest, right to the last drop.
http://www.aridbilge.com/

[The Bigfella]

My primary bilge pump is a tiny little thing - tucked down beside the keelson - but it sits right next to a big monster. I've got two separate pumps running off different switches and different batteries. The smaller one obviously has a smaller pipe - so less volume of water comes back after the switch off. It gets the water much lower than just the big pump - which only ever gets to work (hopefully) when I test it.

[Dan McCosh]

FWIW, we have a four-foot lift to the waterline with a Rule 3800 gpm pump. A flapper-type check valve at the pump has been trouble-free for a decade or so. It was installed to cure the same cycling problem. It's in a 1.5 ins. line, however, and as a result the back pressure seems to set it quite solidly, with little or no back leakage. The outlet is via the cockpit scuppers, with a T-connection just under the cockpit floor. Also, we set the float to keep the pump inlet well under the level of the bilge water, as a check against any oil leakage being pumped out--this is a critical issue in these waters.

[kulas44]

Been here done this. Get a good Jabsco diapram bilge pump, strainer, and a WaterWitch pump switch. A small sump is a big help. The WaterWitch switch runs the pump for several seaconds after "no Water" and the diaphram pump will keep sucking, removing ALL of the water. I've tried everything and this works. You still need crash pumps, and a Rule 1500 ain't it, maybe a 4000 gph as a minimum.

[py]

If you can get your high point and vent/syphon break as close as possible to the bilge pump, rather than near the discharge end, more water will drain overboard, and less back down into the bilge. Shouldn't matter if you have a 20' run of pipe, provided it all just drains outboard rather than back into the bilge.

[leaotis]

just give the manual pump a couple of licks daily and keep the electric pump from coming on.