Put new diaphragms in one of the AP100 pumps I have and thought I would post some pictures.

I'm going to get away from these pumps. They were marginal in the pressure/flow they will deliver for the depth of my pond and raising the pond level another foot from when I originally started using them did not help. Thread with pressure/flow calculations here for water head pressure

I've also run into another puzzling problem. The pumps specs say they have a max pressure of 6.53 psi. Even after rebuild some of them I can only get 3 psi, which obviously will not work in 8-10 ft deep water. I can find no air leaks in the air box, valve manifold or any other reason for the lack of pressure. These are linear type motors actuating diaphragms on each end and the only conclusion I can come up with is the armatures are weak and not pulling full stroke. They pump air fine, hold pressure fine, just do not build full pressure.

I will probably go to a rotary vane or rocking piston pump later this summer.

At any rate, pictures below of the inner workings and rebuild. Kits are $8-12 depending on where you get them. Pictures will be in two posts because there are several of them.

Edit 4-3-2018 youtube video Rebuilding AP100 pump

Second set of pictures.

Some installation notes:

The white nylon wear washers that keep the diaphragm retaining washers from chaffing the diaphragm are a little tricky. The inner is easy as the plastic pins keep it in place. But the outer one a person needs to keep it manually centered while installing the retaining nut or it will fall down out of place. This is even a problem at the factory because I have rebuilt ones where the washer had fallen out of place during factory installation. It is not hard, just takes some attention to detail.

When installing the flapper valves, diagonal cutting pliers can clip the retaining tab off to get the old ones out and also to clip the excess installation portion off after installation. Take care to put them in the right direction. The valve side goes on the cupped side of the valve body. They pull through a little easier if you spit on the tab first.

The diaphragms are a little tricky to get stretched into place. Have to remove the nylon retaining ring to get the old one out of the body, finesse the new diaphragm into place and replace the retaining ring.

It is not necessary to remove the cover off the motor to rebuild the diaphragm assemblies. But I have found it to be easier in that you can reach in and force the armature toward you to make it easier to get the parts assembled to the motor shaft. Otherwise the motor shaft tends to want to go away from you making it hard to get the parts and retaining nut on the shaft easily.

Clean the intake filter. In the kit they give a new seal for the air box but there is rarely a need to take the air box apart. It can get some debris in it from a failed diaphragm but I see no need to take it apart. I did once just to make sure that was not a source of an air leak, but it was not needed. There is also some filter material in there just to keep rubber pieces from exiting the outlet in case of a diaphragm failure.

They put some odd pieces in the rebuild kit. They put a new seal for the air box, but the air box rarely ever needs to be taken apart. Yet they do not put some parts that I can see might be needed (but so far after a half dozen rebuilds I never have). For example they give you an air box seal yet do not give you one for the valve manifold which is much smaller and more prone to damage and has to be taken apart when you replace the valves.

All in all I have been happy with these pumps going on 3 years now up until now. Now I have three of them I can not get to pump up to over 3 psi, so will not work with the depths I need. This I am disappointed in. They run fine, they pump air fine, they will just not develop the pressure I need for the depth I have so will not work as intended any longer. And I have no idea why, other than the guess that the motor is weak and not pulling the diaphragms to full stroke. I have checked for leaks in the air box, connecting tube and valve manifold assembly.

I was asking a lot from these pumps and they have preformed adequately up till now. But I think it is time to move on to a more robust pump. The diaphragms last about 6 to 12 months of 24/7 running in my experience (summer running, no winter temps). Rebuild kits are readily available. They recommend max depth of 11.5 feet but I would recommend no more than 8 feet. Air flow drops off rapidly with depth due to the nature of the linear actuated rubber diaphragm pump design.

Added to my watched topics.
My diaphragm 120 pump is about 7 months old running 8 hrs a day.
I have a rebuild kit on hand.

I am an absentee pond owner and my pump is on a timer. If the diaphragm fails and it continues to run, will the pump be damaged? Heat build up or some other issue?
Trying to gauge if I should rebuild as a proactive measure.

The few times I have seen blown diaphragms (in industrial settings) the results were massive reduction or complete loss of air flow without any damage to the remaining pump parts. It keeps trying to pump, but to no avail, the rubber has ripped. It would behoove you to reduce the amount of time the pump is running with a compromised diaphragm, but I would think that it could run for days after a diaphragm rip. I think it would be a different story if you removed the diaphragm completely and ran the pump. Even the remaining rubber of a blown diaphragm yields some shock absorption to the moving parts keeping them from self destructing.

Heat and the lack of humidity are likely the worst enemies of the diaphragms. Sun light would be a big killer, but if you have it covered or the diaphragm is not exposed to the daylight it's moot point.

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.

Can someone link me To the inexpensive hiblow rebuild kits?

I'm seeing $100 +.

https://www.septicsolutions.com/septic-parts/septic-air-pump-parts/hiblow-rebuild-kits?gchildcat=hp-100%2f120-parts

Snrub:
Tried to PM you but I think you have disabled the PM feature.

Just got a PM the other day from someone else. I don't always notice my PM's right away but I think it is still working.

I just sent you one.

I was getting "user not found" message when trying to PM you.
I responded to your PM ok.
Gremlins in the software....

Anyhoo,

Can you share your source for inexpensive hiblow rebuild kits?