Monday, December 9, 2013

Onga JM100 Pump Teardown

The pressure pump connected to our rainwater tank failed the other day.  It didn't stop working, it just sounded really wrong and got too hot for the short amount of time it was running.  I'd previously replaced the motor run capacitor on this particular pump and was reasonably familiar with its operation.  As a first step I checked the things I know best, the electrical components.  The 10 uF motor run capacitor was fine, it was reading a perfectly acceptable 9.8 uF.  The winding resistances were however way out of whack.  When I last repaired the pump I took note of the readings, and they had changed significantly since then.  They were now about one sixth of what they used to be.  If some of the windings are shorted it pretty much means it's beyond repair, but I decided to pull it apart for fun, and to see if there was something obvious that could be causing the problem.  So even if the pump can't be repaired there's at least a guide that others can use if they need to pull their pump apart.

Warning - This article describes equipment and circuits that operate at high voltages.  Don't attempt to repair any high voltage circuits if you're not trained to safely work with electricity.  You may be seriously injured or even killed.  For further information read the blog's Terms Of Use.

I hadn't done anything like this before so I tried to find some sort of service manual.  Although not an exact match but the parts diagram in this manual was a fairly accurate representation of how the pump was constructed.

I started by removing the pump head and taking off the fan cover.

Fan cover removed

Pump head removed
At this point I took a moment to inspect the impeller on the motor and the diffuser in the pump head for any signs of wear.  Everything looked fine.

Brown diffuser in the pump head
The next step is to remove the pump stand from the bottom and disconnect all the electrical wiring.  If your not sure how to reconnect everything take lots of photos for reference.  Removing the fan at this stage is a good idea.  It may take some doing, but it can be pried off with a flat bladed screw driver.

With the fan removed, a screwdriver can be used to lock the shaft in place while the nut holding the impeller on to the shaft is removed.

Pump stand removed
Removing the impeller seemed to disturb a colony of ants inside the motor.

Ants inside the motor
After removing the impeller you'll be faced with the layout in the image below.  To remove the black plastic plate the seal on the shaft needs to be removed.  Once again it may take a while to figure it out, but it can be pried off with a flat bladed screwdriver.

Seal on the shaft
Ignoring the ants for the moment, all that's left to do now is to remove the end plate of the motor.  There's another rubber seal on the shaft that can be removed easily.  Once this is done the bolts holding the plate on can be undone.  To remove the plate, gently tap the other end of the shaft where the fan used to be attached, this will push the plate off.

Motor end plate
You now have access to the rotor, bearings, and stator coils.  Apart from the ants, I couldn't see anything out of the ordinary here.  The bearings seemed to turn freely and there was no obvious damage to the motor windings.

Disassembled motor
I used a compressor to clear all the ants out and then reassembled the motor.  It didn't sound any worse, so I'll take that as a win.  I'm still not entirely sure what caused it to fail though.  It could have just been a random breakdown of the winding insulation, that caused part of the motor to heat up causing the insulation on other windings to break down.  Maybe the ants damaged the winding.  Who knows.  One thing is for certain, this motor has reached the end of its life.


  1. Very helpful thanks! I wanted to replace the bearings, but I couldn't see how to remove the fan. Your photo clarified this.