Pond Boss Forums AERATION Systems questions Koenders Diaphragm Repair or "Thanks, Bill Cody!"

After lasting an uncomplainably long 6 1/2 years, the diaphragm on my Koenders windmill passed on about a month ago (leaving me wondering if it had experienced any degraded performance over the Winter that may have contributed to the partial fishkill I had under the ice ???).

Our own Bill Cody had always stated he could provide help on how to replace a diaphragm, so I asked him for assistance. Bill was able to identify which era of Koenders I had (mine has a Serial Number, but no Model Number, posted on it) from my description and a photo. And although he virtually never mentions it here, he can also provide replacement diaphragms and check valves, as well as rubber membrane diffusers (an upgrade for me, since my windmill came with a less efficient airstone) for Koenders windmills at the lowest price I could find. Throw in some useful tips, and I was glad I asked Dr. Perca for help.

For the record, here are some steps to follow that may be useful to any Koenders owners needing to replace their diaphragm:

1. Pick a day with a little wind, enough to turn the mill slowly. Dead calm would be OK to work in, but makes it hard to see the results of your efforts. Really windy days are poor times to try to control a windmill and hold it still for maintenance.

2. Lasso the tailfin and tie it off to something (in my case, the fence that keeps grazing cattle from trashing my windmill) so the upper assembly of the windmill cannot turn as the wind changes direction. I tied it at an azimuth angle that let some, but not all, of the wind's force keep turning the vanes slowly, a position that let me lean a ladder flatly against one side of the triangular tower and access the upper assembly easily.

3. Use a good ladder. I am lucky to have a good solid fiberglass and aluminum 10 foot step ladder which was just the right height for working at the top of my 12 foot tower. Extension ladders work OK as well, provided they can be set short enough to lean on the tower, not the rotating windmill/pump/tail assembly (I did this for an inspection once, and it is disturbing, to say the least, to have the ladder try to turn with the upper assembly even AFTER you have done your best to secure the upper assembly with a rope). I tied the top of my ladder to the tower to eliminate any surprises.

4. Tie off the vanes to keep them from spinning. I have in the past managed to lasso the vanes from the ground, but if you have secured the upper assembly as mentioned above and the vanes aren't rotating too fast, it is easier to do this from the top of the ladder. Tying them to the top of the tower also lets them be untied without climbing down, nice for checking restored air pump function while at the top of the ladder. I would not want to check this while I was at the top of the ladder if there were enough wind to spin the vanes very fast, though.

5. The actual mechanical repair is fairly simple. For my windmill, it consisted of removing the top cover on the "can" that houses the pump assembly to expose the diaphragm, then removing the inner cover that holds the diaphragm (2 reinforced rubber pieces, a large outer "doughnut" and a smaller "doughnut hole" that goes in the center") and the check valves. Cody had provided me with new parts that were indistinguishable from the originals, except that they were brand new. The only surprise here was that the inner cover was secured by screws needing a square-shanked driver (what I think of as a "security" bit), S3 sized. Fortunately, I had an S3 bit in a multi-tip screwdriver set.

Remove the old diaphragm parts (and check valves; if you are replacing them, it is done at the same time), put the new diaphragm parts back in the same position and reassemble in reverse order. This is where I had the most difficulty, as the clearance between the rubber diaphragm parts and the screw holes is minimal and it took a few tries (and about 10 minutes spent speaking in mostly Anglo-Saxon terms) to first get all four screws on the inner cover started (and then tightened) and then to position the piston (with the new diaphragm on it) so that the twelve bolts for the top cover could be started as well. I found marking the locations of the four inner cover screws with a piece of yellow keel (construction crayon - pencil would have worked as well) to be very useful, since the inner cover obscures these four positions. Without the markings, you are working by feel (and four letter words) only.

THIS IS ALSO ONE PART OF THE JOB WHERE YOU WANT THE VANES SECURED, NOT ROTATING, EVEN IF THERE IS ABSOLUTELY NO WIND! Once the old diaphragm is removed, there is nothing to hold the air pump piston, which attaches to the vanes via the cam that moves it up and down as the vanes turn, centered in the can. Turn the vanes and let the piston drop, and it flops off to the side and requires re-centering before it can be lifted (by rotating the vanes) back into position to install the new diaphragm. There is sufficient clearance to allow for finger pinching, cutting, or worse (?) between the heavy steel piston and the heavy steel can. I didn't get hurt when I untied the vanes to examine how the pump worked at this point in the process, but if the wind had come up suddenly I might not have escaped with my fingertips intact.

6. This is an excellent time to check the many nuts and bolts on the top end of the windmill for tightness. These should be examined periodically. Mine are nice and tight, thanks to locknuts and minor corrosion.

7. I also took this opportunity to grease the base of the upper assembly where it turns on the tower. We added a second ladder to one of the other sides of the tower, and Fish Wife greased the bottom and top of the shaft the upper assembly rotates on, the latter as I lifted the upper assembly by a couple of inches. Lifting the upper assembly pulled the shaft off the air hose which attaches to it's bottom, so we greased the outside of the air fitting there before we put the air hose back on it (this is also a rotation point).

8. Given the large variety of screws, nuts, bolts, and assorted phantasmagoria that make up a Koenders windmill, in combination with the remote location many of them are installed at, probably the best advice I can give for this job is BRING LOTS OF TOOLS WITH YOU. I only have a 250 yard walk from the windmill back to the house/workshop to get more tools, but some folks may have to go much farther than that.

Once reassembled the windmill pumped just fine. I had plenty of time left to replace my old airstone with a rubber membrane diffuser I also got from Bill. Smaller bubbles from a diffuser mean more efficient water lifting than with an airstone. I will note that farm supply stores such as TSC are an excellent place to find tubing-to-pipe thread adapters, especially at this time of year when they are stocked up for field sprayer repairs.

After the new diffuser was placed in the pond, I waited in our canoe for a few minutes for the wind to blow so I could hear the Don Ho music ("Tiny Bubbles") coming up from under the water. I was slightly worried that the month long period without forced air aeration might have stratified the pond and allowed some bad decomposition gases to build up near the bottom, but a smell check on the boil coming from the diffuser revealed no rotten egg or other nasty smells. Spring water temps and winds have probably kept the pond pretty well mixed since the old diaphragm failed.

I add this picture to the Forum collection of "Strange Objects Used for Diffuser Bases". In addition to the garbage can lids and snow saucers previously posted by others , behold the Old Kitchen Range Exhaust Hood:


Thanks, Bill!

Theo, That looks like a job well done. Its always a surprise to see those 4 bolts requiring the square driver. If you have the brass 3/4 inch hex on the top outlet centered on the 12 bolt cover there is an O-ring in where the top check valve went that is can be bad. Since you have a diffuser that may give some additional back pressure compared to the standard stone you may find leakage at that threaded point if the oring is bad. You can also thread tape (seal) that bushing and seal if it does leak.This will give you another reason to get the ladder back out prior to another 6-7 years diaphram replacement