Abstract: A sliding-vane rotary compressor includes an intake pressure control valve disposed within a cylinder head of the compressor and located between an intake passage for a fluid to be compressed and a low pressure chamber. The control valve comprises a pressure responsive element such as a vacuum bellows or diaphragm actuatable in response to either the pressure in the intake passage or the pressure in the low pressure chamber, a pilot valve connected to the pressure responsive element, a pilot passage adapted to be opened and closed by the pilot valve for developing a difference in pressure, a main or differential piston movable in response to the pressure difference developed, and a throttle mechanism responsive to the movement of the piston for varying the area of an orifice through which the intake passage communicates with the low pressure chamber.