Dissecting a Bilge Pump

I recently took 5 bilge pump based thrusters off of a previous rov to use with a new robot. To my dismay I noticed some discoloration under the surface of each pump. My first thought was that water had gotten in and corroded the internals. The propeller on one of them wouldn’t even turn a full revolution at first. I connected each one to a power supply and surprisingly they all still work, though they don’t sound very good. I figured this would be a good opportunity to take one apart and not only figure out the problem but also see how a bilge pump works. These pumps are a few years old and have been used in two competitions (both times going down to 13 feet, the first time for only a few minutes, the second for half an hour). Other use has been limited to backyard swimming pools. Do note that these are cheap bilge pumps (the brand is Seachoice), so the internals may be different than more expensive (and hopefully better quality) pumps available.

A pipe cutter works very well for cutting into a bilge pump.

Almost the entire end of the pump is corroded. The shaft seal seems to consist of an o-ring type seal on the outside of the plastic casing followed by some sort of goop (part of the goop is on the left of the output shaft).

This is inside the base of the bilge pump. There is a metal plate holding the motor to the plastic housing.

This is the bottom portion of the pump. Here you can see the metal bracket securing the motor to the casing. On the right side of the case is the sealing for the wires. There is some corrosion in this portion of the pump, though it doesn’t seem as bad as the other side.