> On the other hand my work project is to attempt to emulate something
> very similar consisting of a piston to pump helium gas in a cooler.
> The piston moves about 4 to 5 mm at max movement, and has an LVDT
> attached to provide positional feedback. The whole thing also gets
> bogged down in drying to minimise the vibration of the mechanical unit
> to stop the satellite it will be on from vibrating and spoiling the
> nice pretty pictures the camera will be taking.

Two identical opposed pistons and valving machined in the cylinder walls
as slits ? (see boxer motors and Jumo 205 WW2 era aircraft diesel engine).

Peter

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