Abstract: A rotary compressor, expansion engine, or the like. Two interengaging rotors rotate in a casing structure. The optimum number of lobes per rotor is two for pressure ratios up to about three. The first rotor has end plates thereon which open and close larger ports in the end walls. Low pressure dump pockets are formed twice per rotation and these have now been determined to have negligable loss. The first rotor has lobes of small angle so as to reduce a precompression loss. The second rotor has lobes of larger angle so as to improve performance. An interchamber throttling loss has now been reduced. When operating as a compressor machine, the discharge ports start to be uncovered about 15 degrees early for better performance.

Abstract: The machines may function as a rotary compressor, vacuum pump, expansion engine, or the like. Two interengaging rotors rotate within intersecting bores in a casing structure. Two higher pressure ports are located one in each flat end wall of the casing. One rotor opens and closes the two higher pressure ports so as to control the flow of air or gas through same. The optimum number of teeth or lobes for each rotor is two. The port controlling first rotor has lobes of small included angle so as to reduce the effect of a precompression loss. The coacting second rotor has lobes of larger included angle so as to improve performance.

Abstract: A double acting working piston drives a connecting rod and crankshaft. A smaller valve piston is fastened to each end of the working piston. Each valve piston withdraws briefly from its bore so as to introduce scavenge air into a respective annular working chamber. The valve pistons have a centering means and are provided with novel radially restrained piston rings so as to smoothly re-enter their bores without impacting. Other novel features are: inlet nozzle and vanes, rear slide tubes for conducting coolant (such as water) to the pistons, an oil seal which permits the wrist pin to be full floating, and long tie bolts passing through water passages formed in the exhaust port bridges.