Variable pressure recovery

Control valves have been classified into two broad categories according to the nature of the pressure recovery inside the valve: low recovery valves (typically globe style) and high recovery valves (typically rotary style). This relates to the difference between the lowest absolute pressure at the vena contracta in the valve and the downstream pressure in ratio to the actual pressure drop across the valve. With some new developments in rotary control valves this classification has become insufficient and a new concept variable recovery - needs to be brought into wide usage to be able to evaluate the performance of these designs. In a global style control valve, the pressure recovery is fairly constant throughout the valve opening range. The liquid pressure recovery factor, F/sub L/, can be used as an indicator of how low the pressure recovery in the specific valve is, so that high F/sub L/ factors indicate low recovery and vice versa. Globe valve F/sub L/ range between 0.7 and 0.9 for standard designs depending on the valve style, and stay constant at all valve openings when we use the flow-to-open configuration. Globe valves are typically labeled low recovery. On the other hand, the rotary style valves have,more » for example, an F/sub L/ factor of 0.55 at full (90/sup 0/) opening for a ball valve and 0.65 at 70/sup 0/ opening for a butterfly valve. These valves typically have been considered high recovery.« less