Abstract: A rotor (23) is mounted for rotation in a housing (10) having a pressure chamber (31) and an exhaust chamber (33) formed about the rotor. The rotor is provided with slots (36 and 37) which are moved sequentially in pairs into alignment with plungers (48 and 68). When a plunger (48) partially overlays a slot (36), pressurized air passes from chamber (32), through an exposed portion of a slot (36), through plungers openings (49, 44, and 43) to one end of an air cylinder (12) while exhaust atmospheric pressure is presented from chamber (33), through an exposed portion of a slot (37), through a plunger openings (71, 67, 64, and 63) to the opposite end of the air cylinder (12) to permit movement of a piston (83) to drive some external mechanism.