| 摘要 |
PURPOSE:To reduce the time when a prescribed pressing pressure is attained and to maintain the stable pressure with inexpensive parts by interposing a flow control valve to a bypass circuit provided between a pump and a selector valve and providing a stop valve which operates the bypass line at the lower limit of a control pressure. CONSTITUTION:When a change-over valve 19 is opened toward a pressing side by a command for pressing, the entire oil quantity Q1 discharged from a hydraulic pump 16 is supplied through a check valve 18 and the valve 19 to an operating cylinder 15, by which the pressure in the cylinder 15 is sharply increased. When the pressure in the cylinder 15 attains the lower limit of a control pressure, a stop valve 22 is opened by the signal from a controller 26 to operate a bypass circuit 20 and therefore the flow Q3 set by a flow rate control valve 21 is returned through the circuit 20 to a tank. The remaining flow Q2 is therefore supplied to the cylinder 15 and the pressure in the cylinder 15 rises gently from the lower limit of the control pressure until the pressure attains the upper limit of the control pressure, when the valve 19 returns to neutral and the galve 22 is shut off so that the entire oil quantity Q1 from the pump 16 returns through the valve 19 into the tank. |
