Abstract: A compressed air rotary motor includes high and low pressure rotors having peripheral helicoidal threads. The rotors are sandwiched between a circular plate and end wall while an intermediate wall separates the two rotors. Fluid passageways in the plate and two walls control the flow of compressed air initially to a single gap between two threads of the high pressure rotor and thence to at least two gaps between a plurality of adjacent threads of the low pressure rotor following which air is delivered to an annular channel in the end wall prior to exiting the motor.