apparatus for selectively creating a vacuum or increasing pressure or for converting pressure forces into mechanical motion includes a pair of substantially cylindrical housings , each having an airtight chamber therein . a length of a flexible sheet - like material has each end spirally wound around an axle in each of the chambers and extends out through openings in the housings . the sheet - like material functions as a piston and an airtight seal is formed between the material and the opening in each housing . as the axle in one chamber is turned to draw the piston into that chamber , the pressure within the chamber increases . however , when the piston is withdrawn from the chamber , the pressure in the chamber decreases . alternatively , pressure in one of the chambers can be changed from an outside source thereby drawing the piston into and out of the chambers . this causes the axles of the chambers to rotate . other structural embodiments of the invention are also disclosed .