A valve 28 is positioned in the upper portion of the interior space of the bellows 10. A flow of low pressure air is induced inside the bellows when the valve elements 40 move away from the air inlet openings 38. When high pressure air is moved into the central portion of the valve housing 30, the valve elements 40 tend to move radially outwardly to block the air passages 38 and 42, thereby terminating the suction applied to the bellows.