Abstract: A screw rotor machine for compressing air or other working fluid comprises a housing including two intersecting bores axes which together define a working space. The pair of intermeshing rotors are rotatably mounted one in each bore. The rotors have helical lands and intervening grooves whereby rotation of the rotors in connecting engagement is effective to compress the working fluid (or to expand the fluid if the machine is used as an expander). A low pressure port and a high pressure port formed in the housing at opposite ends thereof permits inlet and outlet of the working fluid. The grooves of the rotors each have a primary flank and a secondary flank. The tips of the primary flanks of both the male and female rotors are formed by parabolic arcs which generate major portions of one of the flanks of the opposite rotors. A major portion of the secondary flank of the female rotor is also a parabolic arc.

Abstract: In a rotary piston machine the main rotary piston makes sealing engagement with at least one end wall of the main rotor bore and at least one inlet port is provided in that end wall and is located within the compass of the cylindrical portion of the main rotary piston, the main rotary piston is cut-away to open the inlet port to the working spaces of the machine, which are defined by the main and auxiliary rotor bores, the outer peripheries of the rotary pistons and the end walls of the housing, in order to induce working fluid into such spaces.