Pond Boss Forums AERATION Systems questions Rebuilding Pondmaster AP100 pump

In the case of the Pondmaster (I think the same pump is sold under multiple names) the two diaphragms are what holds the armature in the center of the stator coils. As you know in a linear motor the armature moves in a back and forth motion rather than in a rotary motion like a regular motor. The diaphragms are also what limits the travel of the armature.

As pressure builds the armature resists the pull of the stator fields and when the motor is at stall pressure hardly moves at all. It basically de-strokes as the pressure builds and maximum pressure is determined by the power of the coils ability to push-pull the armature against the pressure created by the diaphragm. Or at least that is my layman's understanding by observing the construction of the device.

But I digress and am not addressing the self destruction part. From my experience when a diaphragm fails the armature goes off center and the permanent magnet in it just attaches to one or the other of the stator coils. It just stops. The armature just stays still so no further damage is done. The coils continue to hum with the 60 Htz AC but to a much less degree than when the pump is actually running and the armature is moving the diaphragms back and forth. I have never had any problem with the pumps self destructing. They just stop working. Rebuild them with new diaphragms and they start working again. I've never had a motor fail (although I do question if they can become weak because of my problems with them not developing full pressure after a couple rebuilds).

One thing I will say is that you do not want to pick them up or move them while they are plugged in and running. The armature runs pretty close to the stator, centered only by the two rubber diaphragms, and if you bump them you will hear the moving armature hitting the stator. Probably not a good thing.

From my research before initially buying my first pump is that this type pump is one of the most efficient there is turning electricity into air flow at their optimal design air pressure. But they gain that efficiency by being not as durable and shorter life between rebuilds than rotary vane or rocking piston pumps. They work exceptionally well in certain applications such as aquariums or shallow ponds, but they are not the most trouble free choice and they are not a good choice as pressure requirements (depth of pond) get near their design limits. That is the way my non-expert experience sees it.