Abstract: Disclosed is a solenoid type electromagnetic operating device which needs a relatively large current only for a limited short period at an excitation start initial stage and is adapted to achieve the speeding up at an excitation start stage and an improvement in responsiveness as well as power saving without increasing a power load on each of a drive circuit and power supply.

Abstract: A variable displacement piston pump of the type in which the hydraulic pressure in a pressure chamber of an output flow variable element is controlled by a proportional electro-hydraulic control valve to control the displacement of the variable element against a spring to vary the output flow within a range between a maximum output flow and a full cut-off and the output pressure or both the output pressure and the output flow of the pump are controlled electro-hydraulically through a closed loop.

Abstract: A control circuit for a proportional electro-hydraulic fluid control valve in which during a transient condition with a feedback control signal varying rapidly the control loop is changed to an open loop to change the transient characteristic of the valve to prevent the occurrence of an abnormal surge. The control circuit includes a control loop changeover circuit designed so that when the error signal is greater than a predetermined level, the control mode of the magnitude control of a control output signal is changed from a closed loop control in accordance with the feedback signal to an open loop control in accordance with an input signal.