Abstract: A precision valve control for an hermetically sealed hydraulic valve system which operates with a solenoid driven magnetic actuator. The magnetic actuator forms a toroidal magnetic force field of varying strength which causes controlled movement of a core rod linked to a pilot. The pilot, in turn, causes actuation of the main disc to the desired valve position. Actual valve position is remotely ascertained, by position of the magnet (or core) within the magnetic field, by means of a Linear Variable Differential Transformer (LVDT). The LVDT creates variable voltages predeterminately related to position of the rod within the magnetic field. The LVDT voltage is compared, by an electronic comparator, to an input command voltage, calibrated to a specific valve position. Deviation between the LVDT voltage feedback signal and input command voltage signal causes generation of an error signal which is amplified and applied to the solenoid to vary the magnetic field to correct the valve position.

Abstract: The valve assembly for the control of flow of liquid from a source of liquid at high pressure to a place of use has at least one restrictive orifice adjacent a movable valve member and valve seat to provide pressure drops in series in the liquid each of which pressure drops is of a magnitude sufficient to maintain the liquid pressure above the vapor pressure of the liquid at the inlet of the valve assembly so that cavitation does not occur. The restrictive orifice varying in flow area automatically in direct proportion to the variable flow area between said movable valve member and the valve seat.