Oil-free compressors: what wears out?

I would guess the teflon piston rings first.


The pump used by California Air Tools does not use a traditional piston and ring. It is a knock off/variation of a Thomas WOB-L pump. Very similar to any piston pump but with two exceptions.

There is no wrist pin ! The piston is directly connected/cast to the rod. The "big end" is as usual, ridding on a bearing on the crank.

The piston is attached to a "rubber" membrane (diaphragm) that is attached to the sides of the cylinder. As the piston moves up, it tilts to one side. As it moves down, it tilts the other way. Reed vales in the head. The "stroke" is very short so the amount of air moved per rotation is very small which is also why these are usually direct drive. The small amount of air moved per stroke also keeps the noise down. Also because the diaphragm seals the top from the bottom, this type of pump can be used for medical purposes, both vacuum and pressure (extra filters required).

Best of all, the diaphragm is easily and cheaply replaceable !