Abstract: When a solenoid has been turned on by supplying current to a coil thereof, the solenoid operation is checked by temporarily ceasing the supply of current to the coil to temporarily deenergize the solenoid. The current flowing in the coil is detected while the solenoid is temporarily deenergized, and the characteristics of the thus detected current are used to discriminate the position of a movable iron core of the solenoid. On the other hand, when the solenoid has been turned off by ceasing the supply of current to the coil, the solenoid operation is checked by temporarily supplying current to the coil to thereby temporarily energize the solenoid. The current flowing in the coil while the solenoid is temporarily energized is detected, and the characteristics of the thus detected coil current are used to determine the position of the movable iron core of the solenoid.

Abstract: A proportional electromagnetic valve includes a valve main body having a valve member, a solenoid to drive the valve member, and an amplifier unit to control the solenoid. The solenoid is attached to one or both side portions of the valve main body. The amplifier unit has a size which is almost equal to a size on the unit attaching surface side of the valve main body and solenoids. The casing of the amplifier unit has an enclosing space large enough such that single printed board having all of drive amplifiers attached there to placed in the casing of the amplifier unit.

Abstract: A differential pressure regulator is arranged in series on the inflow side of a variable throttle for adjustment of a flow rate. An inlet pressure of the variable throttle is led into a primary pilot chamber of the differential pressure regulator. A constant flow control valve is provided in an oil passage connecting an oil passage on the inflow side of the differential pressure regulator with a secondary pilot chamber in order to allow a fluid of a constant flow rate to flow. The inflow side of a sequence valve is connected to the side of the secondary pilot chamber of the differential pressure regulator. The outflow side of the sequence valve is connected to the outlet side of the variable throttle or a tank. The inlet passage of the variable throttle is led into the primary pilot chamber of the sequence valve. An outlet pressure of the variable throttle is led into the secondary pilot chamber of the sequence valve. Further a check valve or a throttle is connected in parallel to the sequence valve.