A normally-open, solenoid-controlled valve includes a stationary valve-seat spindle and a cylindrical valve sleeve encircling and slideable along part of the valve-seat spindle. FORGED STEEL VALVESThe valve-seat spindle has an annular control edge and the valve sleeve includes a pressure-responsive surface which is reciprocably moved into and out of valve-closing contact with the control edge.Bellow Seal Valve The valve-seat spindle includes a flow passage therein extending to and discharging into a plenum region formed radially inward of the control edge between the spindle and the sleeve. The pressure-responsive surface of the valve sleeve is a substantially continuous frustrum of a cone whose apex extends in the direction of the valve opening and which extends radially outward from a sleeve inner diameter A to an outer diameter C (point C) of discontinuity in that surface. Instrumentation Ball Valves Point C is radially outward of the spindle and sleeve centerline at least as far as the point of intersection, B', with that frustoconical pressure-responsive surface of a line normal to the surface and extending through the control edge D when the sleeve is fully-open. The minimum radial positioning of discontinuity point C is a function of the angle of the pressure-responsive surface and the stroke of the sleeve. The high pressure plenum is structured to enhance the valve-opening rate. A solenoid valve driving device includes a bypassing current path of which one end is connected to a point between a first switching device and a first solenoid valve and another end is connected to a point between a second switching device and a second solenoid valve, and an element disposed in the bypassing current path and having a characteristic that causes current to flow from the first switching device side to a second switching device side. By adopting the above described constitution, through current generated when the first switching device is switched from an OFF-state to an ON-state during duty control of the first switching device can be suppressed by the inductance of the second solenoid valve. In this way, one solenoid valve among a pair of the first and second solenoid valves, which is not operated, has a function of suppressing the through current.

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