Maintaining the position of an electro-hydraulic servo valve controlled device upon loss of position command

摘要

A valve that keeps a electro-hydraulic servo valve (EHSV) controlled device such as a fuel metering valve or actuator at the last commanded position upon loss of input command in the EHSV is described. The valve fixes the position of the positioning device within a tolerance of the position the positioning device was at prior to the loss of the position command. Upon loss of the input position command, the valve moves from its spring-biased default position to a position that keeps the positioning device at a position within a tolerance band of its last commanded position as a result of the differential pressure created when the EHSV loses its input position command