Balanced and Standard Globe Valves Operating Load Profiles With Flow Over the Discs/Plugs

Abstract

Standard globe valves have one disc and are used for the majority of valve applications in flow isolation and modulation services. However, as the size of the valves get bigger, such as 8 inches or greater; the operating load requirements get much bigger by the square of the plug/disc diameter. The bigger the operating loads, the larger are the actuators, which increase cost. At some point, it makes sense for economic reasons to utilize balanced globe valves to reduce the operating loads and thereby reduce actuator cost. Balanced globe valves have more than one plug/disc. Generally, balanced globe valves have an inner disc often referred to as the pilot and an outer disc often referred to as the main disc. The pilot is used to balance the differential pressure across the main disc which allows the main disc to open at a lower differential pressure and hence results in reduced force to open or close the valve. In this paper, the variation of balanced globe and standard globe valve required operating load profiles in the forward flow over the seat flow direction, are presented. The relationship of the pilot disc area to the main disc area is presented to show how this relationship affects valve performance. The impact of the operating load reversal during valve closing on electric motor actuators will be discussed and recommendations provided to guard against valve stalling during closing. The parameters that can affect the occurrence of peak loads as percent of valve travel for the pilot and the main seat will be discussed. The effect of pilot to main disc area ratio on valve factor will be presented. The results of the studies on the balanced globe valves will be compared against the performance of a standard globe valve (i.e., not balanced) with flow over the disc/plug particularly in area of valve factors.