Mulitple Bilge Pumps/ Single Discharge

[bucky]

proposed: plumbing multiple bilge pumps with single discharge to through- hull above waterline.
pumps: 2] 1200gph 12v pumps w/ float switch control
1] manual
plan "a": each pump gets it's own check valve, all pumps
connect to a manifold/collector and proceed to a
siphon break and then to discharge port [1.25"-1.50"]. check valves
to be hinge type to present the least resistance to limited pressure
produced by small pumps.
questions:
1] should check valves be located as close to pumps as possible to
reduce the possibility of drainback cycling or as high as possible to
reduce the head pressure for the pumps to overcome on start up?
2] is the use of a siphon break redundant considering the use of
checkvalves?
any insight you might have would be greatly appreciated.
bucky

[cal40john]

Check your pump manual. Some centrifugal pump makers state no check valves should be in the line. One reason is you can trap air in the impeller and the water sitting on the valve can provide enough back pressure that the pump will never clear the air and won't pump. They don't even want low spots in the hose to create a slug of water to overcome.

Centrifugal pumps don't like any backpressure. Your collector shouldn't impede the water in any way. Your collected outlet hose should at minimum be twice the area, so if the diameter of one hose were 1 1/8" the outlet for 2 should be more than 1.6". If you want to use the manual at the same time you have to account for that area as well.

Experiment, get a pump and watch the output fall off as you raise the outlet then try some other simple resistance tests to see how quickly the pump performance degrades.

John

[bucky]

j
you have comfirmed my gut feeling about this plan [a]. rethinking plan, hate to saw more hole in my boat , seems wrong.
b

[bucky]

j
read pump manual, states no check valves to be used. why didn't i think of that?
b

[stillbuilding]

The idea of a single discharge line/thru hull sounds good. Survey authorities will allow multiple collecting lines connected by manifold to a pump and the overboard. Usually specifies at least two alternative pumps with different power sources.

So no problem with the multiple lines. No problem with multiple pumps. No problem with common discharge. Just change your arrangement.

Just means only one pump active at one time. Not sure if can use two pumps via a Y connector to common discharge. Hopefully someone more knowledgeable than I will comment.

[Sumner]

We have installed (haven't finished the plumbing yet)...



...two Rule 2000 pumps one over the other, but they will have separate discharge lines. The upper pump will only come on if the lower pump is overwhelmed (we have a major problem).

If these pumps went to a common manifold and then out a single line what would keep the water from getting to the manifold and then trying to go downhill (the route of less resistance) back to the other pump. Only a check valve would prevent that and one isn't suppose to have one of those in the line.

Another hole isn't going to be a big deal as it is going to be above the waterline. At least ours are. Our boat came with one manual and one electric and two discharge hoses. I'll drill the hole and add the third discharge hose.

Here is our install to this point and I'll finish the new discharge lines when we return. Also there will be an indicator light on when the bottom pump is running and an audible alarm if the top pump ever kicks on......

Endeavour Plumbing page 16

Sum

[Cheechako]

I have had less than stellar results tring to combine hoses. Also.... what if you want to run two pumps at once? I suppose you could use a 3 way or 4 way (?) valve.

[GASP]

Here is a small suggestion. I stacked by float sensors so the dual big pumps come on at different bilge levles and discharge to a common hull valve AFTER anti-siphon loop in each hose. I also put in a small positive displacement pump (wash down/water supply pump) with discharge to the cockpit that has a function of coming on at the lowest level, a drip pump if you will. Over a six foot lift to cockpit discharge so centrifical pumps did not function. The drip pump is a early warning system that I have a leak into the bilge. Nothing like getting your feet wet to figure out you have a leak.

[sck5]

I have two hoses and two holes in the hull and no check valves. Keep it simple and clean, at least for the bilge pumps.

[Ziggy]

The Johnson L4000 bilge pump comes with an integrated check valve. The manual states:

The L4000 pump comes equipped with an integrated check valve to minimize back flow of water, however, over time water will seep back into the hull when the pump is not running. The use of flapper check valve will reduce maximum flow performance.

You can find more info here. The L4000 is rated at 4000 gph at zero head, but at a more realistic head it's closer to 2000 gph that you are looking for. Manual diaphragm pumps also have built in check-valves at inlet and outlet.

If the discharge thruhull is located so high above the waterline that it will never be submerged, you don't need a siphon break. But any check valve can get stuck open if a piece of debris lodges inside, so I would not relay on them completely. In your plan a) I would add a manual shutoff valve in the hose from each pump where it enters the manifold, so you could close it off if a check valve fails.

A separate thruhull for each pump would avoid all these complications.

[stillbuilding]

Originally Posted by GASP

Here is a small suggestion. I stacked by float sensors so the dual big pumps come on at different bilge levles and discharge to a common hull valve AFTER anti-siphon loop in each hose. I also put in a small positive displacement pump (wash down/water supply pump) with discharge to the cockpit that has a function of coming on at the lowest level, a drip pump if you will. Over a six foot lift to cockpit discharge so centrifical pumps did not function. The drip pump is a early warning system that I have a leak into the bilge. Nothing like getting your feet wet to figure out you have a leak.

Further to your comment on using the positive displacement pump, I would like to use a PDP to discharge at higher point also (I have large cockpit drains which could be used). Using a strainer is an obvious imperative. These electric pumps are obviously not submersible. Some seem to manage a lift up to 5m but not sure what this would do to capacity but may be good for small volumes as you are doing.

Anyone using a large Johnson flexible impeller pump running off an electric motor as bilge pump with a float switch? Seen them hanging off the main motor or course but that requires attendance.