<p>A vane compressor has a communication passageway extending between a discharge pressure chamber and vane back pressure chambers. A valve is formed of a ball received within a ball-receiving bore and displaceable for opening and closing the communication passageway depending upon discharge pressure, a coiled spring urging the ball toward a valve opening position, and a stopper for stopping the ball in the valve opening position. The ball-receiving bore has an axial length smaller than an inner diameter thereof such that part of the ball is projected from the ball-receiving bore into the discharge pressure chamber when the ball is in the valve opening position.</p>
