Abstract: 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 However, when the piston is withdrawn from the chamber, the pressure in the chamber decreases.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.