SHURflo Bilge Pump Conversion

 

SHURflo makes a bilge pump with magnetic coupler between the motor and the impeller.  This avoids the use need for a seal around a moving drive shaft or a dynamic o-ring seal.  Of course they never intended anyone to submerge there pump in 180 feet of water but I they build a pump that should be able to do just that.  SHURflo was kind enough to provide me with one of their Mag Drive Bilge 1000 pumps, model number 1780-120-010.  Here are the specifications: Volts:  12  DC; Amps: 3.75; Fuse Size 6.0 amps; Open Flow: 1000 GPH (Gallons Per Hour with no lift. These pumps are only indented to lift water 3 to 6 feet.)  Duty Cycle: Continuous (Meaning it should not burn up if left running).

Click any image to enlarge it.
4 screws hold the motor and impeller in the housing and also attach the cover for the float switch.
The is a flow switch is a plastic donut with a magnetic ring at the top and a hall effect switch in a sealed plastic tube.  I will reinforce the seal where the wires enter the tube with epoxy.
The electronic control for the float switch is in a sealed compartment above the motor.  The power supply wires also enter this housing.  There are 3 power feed wires:  1 positive, 1 negative and another positive that can be used to turn  on the pump without the float switch.  I will reinforce the seal around the wires with epoxy on the inside and outside.  Since there are only 2 screws applying pressure on the o-ring seal, I will also epoxy the two parts back together being careful not to get any epoxy on the motor.
1 screw hold the impeller on, but it is really not needed because the impeller is glued to the magnet and that actually holds it in place.  The impeller's magnet fits loosely over a spindle in a cup.
The cup and spindle can be removed to reveal a second larger magnetic ring inside.  The cup and spindle are sealed to the the motor housing with another o-ring. This one I will not seal with epoxy because it would be nice to be able to clean the impeller if needed. 
This is the same pieces turned to face downward, which would be their working orientations.  The magnets are both rings about 1 inch tall and both have 4 north polls evenly spaced around the ring.  Surprisingly there is nothing more than a light coating of grease on the plastic spindle.  The impeller's magnet simply rides against the bottom of the cup.
  I have not tested these yet, but I bet they survive 200 feet which will make it the perfect bilge pump for the sub a good and easy thruster for home built ROV projects.  The bad part about the ROV potential is the price.  The SHURflo Mag Drive pumps retails for about $64 each.