Bilge Pumps and back flow

[preservedkillick]

So I tear the Rule 2000 out and the hose before the refit. I flicked the switch and it ran for a few seconds..no further thought.

18 months later and I'm putting the pump back in, all cleaned up and tested in a bucket. Looks great. Dump some water in the bilge and the thing starts cranking. Really moves water..until the float shuts off, then the sizable hose full of water flows back to the bilge. Just enough for the pump to turn on, fill the hose then shut off, over and over.

What am I missing? No check valve, would rather not have one. I can't put a high point in the hose any nearer the pump.

Killick

[jarcher]

That happens. You need to raise the float switch high enough that a tube full of water dumped back into the bilge does not trigger the float.

[jfdubu]

Why not put the check valve in? I have one one each of my bilge pumps and it eliminates the back flow problem. The check doesn't need to be at the high point of the hose, just someplace where you can get to it.

John

[scottyt]

jfdubu check valves are considered bad. a rule type pump can not produce a lot of pressure, if the valve gets even minorly stuck the bilge pump does not produce enough pressure to open it. also if you are using one with an underwater discharge from the pump to keep the ocean out, if it gets stuck open then the boat sinks.

[sailingdog]

The check valve, if located low enough in the hose to prevent any significant backwashing from occurring is likely to have enough water above it in the hose to prevent the rule pump from being able to force it open again.

Originally Posted by jfdubu

Why not put the check valve in? I have one one each of my bilge pumps and it eliminates the back flow problem. The check doesn't need to be at the high point of the hose, just someplace where you can get to it.

John

[jarcher]

It occurred to me That another solution to your problem is to put a high point in the hose shortly after the pump, if you can. So the hose would come from the pump, go up 12 inches, come down, go to the thru hull, up 12 inches above that, then down to the thru hull.

This is not ideal, as anything that makes the pump have to work harder reduces flow, but it is better than a check valve, which reduces flow even when it works properly.

However, if you need as little water in the bilge as possible, then this might be a viable solution for you.

Oh, if the thru hull is high enough - at least 12 inches above the water line when your boat is on its ear, then you can avoid the 12 inch rise at the thru hull.

[preservedkillick]

Today I tried putting a high point in the hose as close to the pump as possible, then a the hose was downhill to the through-hull. It was better, but still cycled a number of times until it eventually stopped.

Looking at it, I think that my bilge is part of the problem. Alberg's have fairly deep bilges with straight sided walls. I'd need to raise the float switch 18 inches until the sides of the bilge flair out.

Not sure I can fix this w/o a check valve, or a getting a much smaller pump that uses a much smaller hose diameter.

[Sabreman]

Sailingdog is correct as always. I'll be blunt. Do not install a checkvalve. Most bilge pumps are centrifugal and do not have enough power to push past the backpressure on the checkvalve. The proper solution is to install a vented loop as close to the pump as possible. he top of the loop must be above the highest point of the hose run. The vent breaks the backflow suction.

Case in point - When I purchased our current boat, a checkvalve was installed about 6 inches from the pump. For 3 months, I couldn't figure out why the pump couldn't evacuate the line. A tropical storm came by, dumped a bunch of rain, some of which came down the mast and emptied into the bilge. The pump came on ran until the batteries died. The power in the marina went out and the batteries were shot.

I ripped out the valve, installed a vented loop, and we've been problem free for 5 years.

Listen to the Dog - he's right!

[SteveInMD]

Reducing the diameter if the hose will reduce the amount of back flow too. Of course this also reduces the pumping rate. Some people install a small pump at the bottom of the bilge with a small diameter hose, and then install a larger pump a bit higher with a larger diameter hose. The larger pump only operates if the small one can't keep up. However, this may be a bit complex for a 30 foot boat.

[jfdubu]

As always There are many ways to solve a problem and yes most check valves do require a lot pump head pressure to open, But this one,

46835K32

$7.10

From Mcmaster Carr, opens with .5 psi which is very close to the pressure drop you get with a 12" loop. Both my bilge pumps have these valves and they work fine and the pumps are the cheap Rule 800 gph pumps. These have been in and working maintence free for 5 years. My bilge pumps out of the boat thru a port 6-8" up from the water line so I am not worried about my boat sinking from a failed check valve