I went to aircraft maintenance school in 1975. The school was Clover Park Voc. Tech. in Tacoma, WA. I was a farm boy that loved airplanes and I had learned to fly 5 years earlier when I was in High School. I’ll save the story about how I decided to leave the farm to pursue a career in aviation for another time. The school I went to was pretty unique at the time because students worked on the flight school airplanes as well as customer aircraft under the supervision of our instructors.
One of the first things you learn is to watch out for the trailing edges of the ailerons of a Cessna. They were just the right height to put a waffle print in your forehead. The second thing I learned was that some jobs were going to be messy. One of those jobs was servicing landing gear struts with fluid. There was no good way to tell if a strut was low on fluid or not unless you went through the process to ensure that the struts are full.
The method was pretty much the same for all the aircraft we worked on regardless of the manufacturer. I would have to drag out a set of jacks, provided that they were not already in use by someone else, and get the plane jacked up high enough to get the tires off the ground with the struts extended. Then, I’d have to release the pressure in the strut, which always sprayed some oil around. Now it was time to get oily. The idea was to connect a hose to the top of the strut, run that hose into a container of hydraulic fluid and then physically lift the tire to compress the strut. This would force all the air and foam out of the strut. Pulling the tire back down was supposed to pull fluid back into the strut. Do this another time or two on each strut then compress the strut fully and disconnect the hose. Usually there was oil running down the strut, dripping on the tire or brakes. This is how all the service manuals said to do it. Who was I to question it?
Once I got my own shop started in 1983, I discovered that it was tough to get enough billable time. I flat rated inspections and normal maintenance items so any way I could save time saved me more money. I built the first 16M- SST Strut Service Tool for my own use. It was simple and saved time by making the process clean. I would not spill any fluid so there was no clean up and I didn’t have to disturb the Schrader valve. Slow leaks caused by leaking Schrader valve gaskets or valve cores were eliminated. Quality went up and time required went down. I was more productive. At some point we began selling the 16M-SST to our customers.
The next evolution was the 16M-SST2 Pro Series Strut Service Tool. This was an improvement because it incorporated two tanks and a frame to hold them. One contained clean fluid and the other collected the overflow, foam and excess. It was also
easier because it incorporated check valves that let me use longer hoses and the unit could set on the floor while I manipulated the landing gear. It was safer, clean and a bit faster than the standard 16M-SST. This became the choice for our customers that were professional mechanics.
One day I got a call from one of those professionals. He told me that he loved the Pro Strut Service Tool except that he couldn’t get it to draw fluid into the strut when the strut was completely dry after replacing the seals. The empty strut could not develop enough suction to pull the hydraulic fluid into the strut. This got me thinking!
Why must we suck the fluid into the strut? What would be wrong with pushing the fluid into the strut under pressure instead? I rigged up one of our commercial hydraulic pumps with the proper fittings and fluid and headed to a local FBO to test the theory. It worked great and it was so fast. I could extend the strut under pressure and let the weight of the aircraft push the excess fluid out. We did not need any jacks. There was no clean up. The aircraft was never in danger because it never left the ground. The commercial pump had some limitations though. It didn’t have enough oil capacity and I still had to use the 16M-SST to release the pressure and capture the excess fluid. I thought we could do better.
We took the idea of the pump and then combined it with the Pro Series Strut Service Tool to create the 16M-PSF Pressurized Strut Filler. This gave us more than a gallon of clean hydraulic fluid on the supply side and a separate tank to collect the excess fluid. It only required one connection and a couple of minutes to service a strut. You won’t even have to remove the valve core. This is a great solution and will greatly increase efficiency. Please watch our video that shows just how much simpler, safer and cleaner this new system is.
The 16M-PSF is a new product for us but it is now available direct through Bogert Aviation or through our distributors. For those of you that have the 16M-SST2 Pro model, we offer a bolt on modification to turn your unit into the new pressurized strut filler.
A patent application was filed on the new process and the 16M-PSF tool.