A pressure regulating circuit in which by adjusting air pressure to be supplied to a pneumatic cylinder pressure chamber (4), the force counteracting a load of a workpiece (W) attached to a work piston (P) is applied to said work piston (P), comprising:
- a main valve (6) having:
- a main air supply chamber (10) connected to a pressure air source (R),
- a main pressure chamber (8) connectable to said main air supply chamber (10) via an air supply valve member (12) and connected to said pneumatic cylinder pressure chamber (4),
- an main exhaust chamber (14) connectable to said main pressure chamber (8) via an exhaust valve member (16) and connected to the outside air via a main exhaust port,
- a piston rod (26) for maintaining said air supply valve member (12) and said exhaust valve member (16) in a closed position when said piston rod (26) is in a neutral position, for opening said air supply valve member (12) when said piston rod (26) moves in a first direction, and for opening said exhaust valve member (16) when said piston rod (26) moves in a second opposed direction, and
- a pressure control piston (20) for reciprocating and displacing according to a difference in pressure between a main control chamber (22) connected to said main pressure chamber (8) and a piston pressure chamber (24) opposed to said main control chamber (22), thereby raising and lowering said piston rod (26);
- a control valve (40) having:
- an auxiliary air supply chamber (46) for receiving pressure air from said pressure air source (R),
- an auxiliary pressure chamber (42) connected to said piston pressure chamber (24) and connected to outside air via a control orifice (84),
- a control valve member (48) for connecting and disconnecting said auxiliary air supply chamber (46) to and from said auxiliary pressure chamber (42) according to a rise and fall of pressure in said main control chamber (22), such that air pressure from said pressure air source (R) is reduced to a regulating pressure predetermined according to a weight of said workpiece (W) before being supplied to said piston pressure chamber (24),
- an auxiliary control chamber (52) being connected to said main control chamber (22) and said main pressure chamber (8) of said main valve (6),
- a control diaphragm chamber (54) being opposed to said auxiliary control chamber (52),
- a control valve diaphragm (58) for opening and closing said control valve member (48) based on a difference in pressure between said auxiliary control chamber (52) and said control diaphragm chamber (54), and
- a control spring (50) attached to said control valve member (48) for urging said control valve member (48) to a closed position;
- a pressure reducing valve (62) being interposed between said auxiliary air supply chamber (46) of said control valve (40) and said pressure air source (R) for reducing air pressure from said pressure air source (R) before supplying the reduced air pressure to said auxiliary air supply chamber (46), said pressure reducing valve (62) having:
- a pressure reducing air supply chamber (66) connected to said pressure air source (R),
- a pressure reducing pressure chamber (64) connectable to said pressure reducing air supply chamber (66) via a pressure reducing valve member (68) and connected to said auxiliary air supply chamber (46),
- a pressure reducing control chamber (72) connected to said pressure reducing pressure chamber (64),
- a pressure reducing diaphragm chamber (74) opposed to said pressure reducing control chamber (72) and connected to said piston pressure chamber (24),
- a pressure reducing diaphragm (78) for opening and closing said pressure reducing valve member (68) based on a difference in pressure between said pressure reducing control chamber (72) and said pressure reducing diaphragm chamber (74),
- a pressure reducing spring (70) attached to said pressure reducing valve member (68) for urging said pressure reducing valve member (68) to a closed position, and
- a pressure reducing diaphragm spring (80) attached to said pressure reducing diaphragm (78) for urging said pressure reducing diaphragm (78) toward said pressure reducing control chamber (72);
- a relief valve (86), provided at the side of said control orifice (84) open to the outside air, for maintaining a difference in pressure between the side of said control orifice (84) connected to said auxiliary pressure chamber (42) and the side of said control orifice (84) open to the outside air within a predetermined range, said relief valve (86) having:
- a relief pressure chamber (88) provided at the side of said control orifice (84) connected to the outside air,
- a relief exhaust chamber (90) connectable to said relief pressure chamber (88) via a relief valve member (92) and connected to the outside air via a relief exhaust port,
- a relief control chamber (96) connected to said piston pressure chamber (24),
- a relief diaphragm chamber (102) opposed to said relief control chamber (96) and connected to the side of said orifice (84) connected to said relief pressure chamber (88),
- a relief diaphragm (100) for opening and closing said relief valve member (92) based on a difference in pressure between said relief control chamber (96) and said relief diaphragm chamber (102),
- a relief spring (94) attached to said relief valve member (92) for urging said relief valve member (92) to a closed position, and
- a relief diaphragm spring (104) attached to said relief diaphragm (100) for urging said relief diaphragm (100) toward said relief control chamber (96);
- and
- a regulator (60) connected between said pressure air source (R) and said control diaphragm chamber (54).