>The oilless types I have seen have use a piston
>fitted to a diaphram. The diaphram is trapped
>between the head and the cylinder and held to
>the top of the piston via a plate.
>The piston is supported by the diaphram and does
>not touch the cylinder wall, this is why it does
>not need lubrication. The rod is connected to
>the crankshaft via a roller or ball bearing.
I have seen another type of oilless compressor, that uses teflon rings in
place of steel rings, and I believe also uses a roller bearing for the
crankshaft. This type tends to wear out the cylinder badly if it gets full
of dust. (this is also somewhat true of the oil type), I think the diaphram
type is quite tolerant of dust (except for the valves-but that is not usually
what fails)
Scott M Ryan
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