Valve position indicator and method

Abstract

Disclosed is a method and apparatus for indicating the position of a hydraulically actuated device by measuring the volume of hydraulic fluid flow in and out of the hydraulic actuator together with separate measurement corrections to compensate for the hydraulic system elasticity and transient flows and for the mechanical clearance or slop in the linkage between the actuator and the device. In a preferred embodiment of the method, the compensation for hydraulic system elasticity and transient flows is preferably made by measuring the relaxation reverse flow when the actuator is depressurized and using this measurement to offset an equal amount of the measured forward flow when the actuator is repressurized in the same direction. Further, the compensation for mechanical clearance in the linkage between the actuator and the device is applied only when the actuator direction is reversed; the amount of such compensation is empirically determined and may increase with wear and tear on the linkage. This compensated hydraulic fluid flow measurement as a position indicator is especially advantageous in indicating the position of a sliding gate valve used for teeming molten steel. The high temperature and corrosive environment about such a sliding gate valve preclude use of prior-art valve position indicators. However, the present invention permits the entire measurement apparatus to be located at a distance from the sliding gate valve.

Dependencies are inferred from the claim text.