Abstract: Although a workpiece can be elevated or lowered according to the invention, the workpiece is prevented from rising or falling abruptly. When the workpiece is elevated with an external force, air supplied from the side of an auxiliary air supply chamber pushes down a pressure control piston. Since a difference in pressure between the side of a piston pressure chamber and the side of an auxiliary air supply chamber is small, air is prevented from flushing from the side of the auxiliary air supply chamber into the piston pressure chamber. When the workpiece is lowered with an external force, the pressure control piston is pushed up, thereby increasing the pressure in the piston pressure chamber. At the same time, a relief valve is opened and the piston pressure chamber is exhausted. By the provision of a relief valve, excess air is not exhausted from the piston pressure chamber. The pressure control piston is prevented from rising abruptly, and the workpiece can be gradually raised or lowered.

Abstract: A pressure regulating circuit in which the piston of a pneumatic cylinder can attain a balanced condition without requiring any adjustment to a workpiece. In the pressure regulating circuit, the pressure in an oil pressure chamber of a pressure reducing valve equals the pressure in a pressure sensitive oil chamber of a workpiece retention member. The pressure in a pressure sensitive chamber of the pressure reducing valve equals the pressure in the oil pressure chamber. Therefore, the pressure in a piston pressure chamber of a main valve connected to the pressure sensitive chamber equals the pressure in the pressure sensitive oil chamber. When the pressure in a control chamber of the main valve and the pressure in a working chamber of a pneumatic cylinder are respectively balanced with the pressure in the piston pressure chamber, the piston P can attain a balanced condition.