Trying to figure out bilge pumps

[Marc_H]

Was wondering if some of you could help me figure out what is going on with my bilge pumps.

What I’ve got - 2018 Lagoon 400S2, Rule 800 bilge pumps, one on each side.

What is happening -

Every 3 months or so, I check the high water alarms that I have installed and also dump in a bucket of water in the bilge to make sure the automatic feature of the bilge pumps are working. When the bilge pump is fully covered up, I can hear the pump turn on but it doesn’t pump any water Basically it cavitates and will not prime. What I do is put some dawn dish detergent in the bilge and mix it a little. Once I do this, the bilge pumps start pumping just fine. After I do this once, and let the bilge pump empty the bilge of water, I can fill it back up and it will pump it out with no problem. Now if just one side were doing this, I would replace the pump and be done with it but both sides ????

It’s as if there is surface tension on the bilge pump and putting in a surfactant gets rid of the surface tension and allows the bilge pump to prime itself.

This ain’t gonna work when there is a real problem and I start taking on water.

Has anyone else had this problem or know what I should do about it.

Thanks in advance

Marc

[Neptune's Gear]

Ive found that centrifugal pumps do this quite a bit. If you just turn it off and on a few times, does it go??

[jefjo]

Weird but surface tension isn't your problem. Sounds more like your'e not getting a good seal around the impeller for some reason and the dish soap acts like a grease allowing the pump to prime until it dissolves and you check the pump again. It doesn't sound like you're air locked but it can't hurt to check the discharge lines for dips. What made you think of putting dish soap in the water??

[Marc_H]

Jefjo . Thanks for the reply.

The only reason that made me think of using dish soap was because of the way the pump sounded when it came on. You could tell that the impeller was spinning freely without a load on it. As if it were trapped in it's own bubble of air. Surface tension came to mind so I grabbed the dish soap and added maybe 10-15 drops and then mixed it up a bit.

I just put a gallon of water in the starboard bilge and the pump is doing the same thing. I wanted to eliminate the dish soap as a variable, so I agitated the water aggressively by hand without the dish soap and could not get the pump to prime. I then put in a squirt of soap and let it sit, no prime. Put my hand in to stir the soap up and immediately, the pump primes and empties the bilge.

It's puzzling to me that both the starboard and port side bilge pumps are doing this. Make me wonder if there is a design flaw with the Rule 800 pumps that came from the factory.

Later today, I'm going to make a video of what is happening and post it here. Maybe that will help in determining the root cause.

Thanks
Marc

[stormalong]

Do you have a check valve in your pump exhaust line? I have one and find that sometimes the pump cannot produce enough force to open it against the pressure on the water standing in the hose - about a six foot lift. Switching the pump on and off a few times usually gets it working. My theory is that the initial pulse of power is just enough to get the check valve to open,

[Qayaq]

I've found that if you have a check valve the pump tends to get an air bubble in the fan, i have drilled a tiny 2mm hole in the outlet. This tends to spray a little water out when the pump is pumping but the pump works fine and it cures the air lock issue.

[Sailmonkey]

I’d bet the soap is foaming in the impeller and allowing the centrifugal pump to start slinging reduced density water against an air lock.

Check your discharge lines to see if you’ve got a low spot that holds water and creates a trap that the pump cannot initially pimp past

[coastalexplorer]

I think that your action of stirring water about a bit. May be the effective action of priming the pump: Much more so than anything to do with the soap liquid. Which of course IF it makes soap bubbles within the strainer basket might be effective in assisting prime.



Quite frankly Rule pumps are not very effective at removing such small quantities of water. However the action of turning them on and off quickly can stir water up enough for it too surge and prime.


Though I have not used it for some time, (long story I will not go into) I have a four meter day boat that has a 3,500 gallon per hour Rule pump which in theory could clear the open cockpit after taking a wave in 90 seconds.



The boat construction was Glass Reinforced plastic over a urethane foam core. and the floor GRP over plywood. Hence with the difference in height between the inside surface of the hull and the top of the floor creating part of the essential buoyancy chambers. Thus when I created the pump tank immediately behind the transom, I cut out a small recess and made good around it with 'D' shaped fiber glass molding with 60 degree sides; the radius of this being only about I inch greater than that of the strainer basket. The 'Flat side of the 'D' facing forward had a very short tunnel under the rear seat too an opening in the floor ahead of it. approximately 3" X 6".



Thus water would flow aft and drop down the hole, pass through the tunnel and totally surround the pump strainer. The pump was powered from a large deep cycle lead acid battery with a Cole Hersee press button switch. Whenever a green wave was taken over the Bow The pump would prime instantly and eject every time.


As time went on the seal around the Dagger-board box leaked, and the wood in the keel rotted. So I opened it up and put in two parallel pieces of wood thus making a four foot long trough to the pump which I thought would feed the pump better. I glassed it all in and poured in water to test it. The result was total failure. The pump would not self prime. I have the same problem that you describe with your Catamaran. On the list of unfinished projects is to box it in and recreate the previous design.



IF you put a Rule pump in a bucket with a bottom only a couple of inches larger than the pump strainer basket, then add water I am sure it will self prime instantly.

[jefjo]

Originally Posted by Sailmonkey

I’d bet the soap is foaming in the impeller and allowing the centrifugal pump to start slinging reduced density water against an air lock.

Check your discharge lines to see if you’ve got a low spot that holds water and creates a trap that the pump cannot initially pimp past

Yup. Follow the lines and look for a dip. I don't think it's coincidence that both are doing the same thing.

[Madehn]

The answer is that your pumps are holding a bubble of air in the impeller area- simple way to keep it from happening is to mount them on a small piece of starboard that is angled so that they are not sitting level- this gives them a "bite" on the water and allows the air to displace - sounds weird but it works

[Mike Banks]

It sounds to me as though there is a dip in the discharge line which contains a head of water similar to the depth to which your pump is immersed. This is preventuing any water from entering the pump impeller. Solution is to make sure there is a hump, not a dip, in the line and all should be well. It does not need much of a dip to starve the pump. This of course assumes no one-way valves in the line. If there are, remove them and replace them with siphon breakers.

[Marc_H]

Solved

Qayaq

You are the man. Yes I do have a check valve in both hulls. It was air lock at the pump that was causing the problem. Drilled a 1/16 hole in the discharge line and sure enough, both pumps will prime and pump water. The 1/16 hole allows just a little water back into the bilge but not enough to matter.

It's good to know now that when I start taking on water, at least the pump will join the fight.

Thanks everyone for your inputs.

Marc

[coastalexplorer]

IF those of you who believe than an air vent in the line is the solution? Why wouldn't you install a I/8" NPT barbed fitting in the hose where you have drilled your hole and run a clear plastic hose from there to above the deck or back into the hose at the outlet?


I still believe that the correct installation requires creating a sump situation, with walls surrounding in close proximity, providing a depth of water sufficient to immerse the filter basket. but with a totally unrestricted flow too it both horizontally and vertically this is the best solution. The only volume of water left by the time the pump stops with be the liquid capacity of the sump.