Small bilge pump to keep it dry.

zz4gta · #1 (**permalink**) 05-12-2010

I'm looking at installing a small bilge pump to keep the boat dry during the week when I'm not around. I like the auto on/off pumps that have a float switch built in. Rule makes one, however, the float switch doesn't come on until the water level reaches 2-3/4" high. Are there any pumps out there that'll switch on around 0.5-1.0" of water depth?

JohnRPollard · #2 (**permalink**) 05-12-2010

ZZ,

There are some pumps that don't use a float switch, but instead switch on at a set time interval. If they detect water, they cycle until it's gone. If they don't, they shut off immediately.

If this is not your "survival/emergency" pump, I would suggest you go with the smallest size possible and install a check valve in the line (to prevent backwash)..

kwaltersmi · #3 (**permalink**) 05-12-2010

I just installed a Rule-Mate 750A and have been happy with it so far. It does have internal "solid-state water sensing technology" so a float switch isn't needed. But you're right, the water level does have to be 2.75" before the pump will kick on. So far, the very bottom of my bilge stays wet because of this.

klem · #4 (**permalink**) 05-12-2010

You will have a lot of trouble getting a bulge pump to actually pump with less water than that. It will difficult to keep the pump from sucking air. When the pump has good suction, it will draw the water down quickly enough that it won't be replenished and will suck air. Once it sucks some air, the water will catch up but then it will have trouble pumping because of having air in the pump. If the pump does get airbound, it will draw down your batteries as it sits there and does nothing.

Do I dare ask why you need to have a pump run on a regular basis? Is there something that is leaking? If it is something like a leaky porthole, it is probably easier and better to fix that.

Gene T · #5 (**permalink**) 05-12-2010

Different ways to do this. You can mount a self priming pump with pickup hose to the lowest part of the bilge through a check valve. Use a float switch mounted very low to start it. Or you can just use something like a Rule automatic, they run every 2.5 min to check for water. You can put a check valve on the outlet if you wish, although this is not a good application for them as they tend to stick and these pumps don't have enough pressure to unstick them. I have both types of these pumps. The automatic Rule drove me nuts when trying to sleep on the boat. I use it now to keep my dinghy dry. Works great for that.

Gene

Maine Sail · #6 (**permalink**) 05-12-2010

Quote:

Originally Posted by zz4gta

I'm looking at installing a small bilge pump to keep the boat dry during the week when I'm not around. I like the auto on/off pumps that have a float switch built in. Rule makes one, however, the float switch doesn't come on until the water level reaches 2-3/4" high. Are there any pumps out there that'll switch on around 0.5-1.0" of water depth?

I have one... it's called a Turkey baster....

L124C · #7 (**permalink**) 05-12-2010

I installed a Diaphragm pump (as opposed to the usual Centrifugal Bilge pump) for my maintenance pump. Unlike Centrifugal pumps, Diagram pumps can be run dry without damage (which is why Centrifugal switches don't kick on until the water is 2.5" high), and have check valves built in, so the water doesn't flow back into the bilge. However, they don't pump the volume required for an emergency, so I have a regular bilge pump with a float switch as well. I used a electric switch which senses the water level for the maintenance pump, attached to a ON/OFF switch. This setup keeps the water level in my bilge to about half an inch on Automatic. Unfortunately, my old diesel apparently leaks a small about of oil into the bilge. The oil coats the electronic switch thereby connecting the two sensors. So, unless I wipe off the sensors, it is no longer shuts the pump off automatically. So I use it in manual mode once a week and it still keeps the water level much lower than the float switch would. If you don't have and old diesel that sits midships directly above the bilge, this shouldn't be an issue. I posted a thread here when I installed it if you want to search for it.