Abstract: A method and apparatus for inducing a controlled, axial load on the stem of a rising-stem, power-operated valve; and for testing the operator response in driving the valve stem against the load. The induced load is controlled both in magnitude and rate while data is collected to determine the operator's mechanical efficiency and its stem load handling capability. The methods, apparatus, and data collected can be used both for intial operator testing and for a periodic test and surveillance program for installed valve operators.

Abstract: An evaluation unit accurately measures the elapsed time between two events. The two events mark the start and stop points of a switching device, such as a motor-operated valve, as it is switching between a first state and a second state. This elapsed time, when compared to a base-line elapsed time or a previously measured elapsed time, provides an indication as to whether the performance of the device has degraded to the point where maintenance or replacement of the switching devices required. The unit includes electro-optical means for individually sensing the occurrence of each event, logic means for selecting the occurrence of either event as the starting or stopping point for the time measurement, and a timing circuit for performing and displaying the time measurement.