Experimental evaluation of restricted lift effects on pressure relief valve stability and system dynamics

Restricting the lift of relief devices is seen as a solution to various challenges associated with installing pressure relief valves (PRVs), particularly in addressing high inlet pressure drops and meeting criteria set by standards such as API STD 520. Previous studies and industry presentations have suggested that restricted lift can mitigate issues related to oversized valves and excessive inlet losses. However, there is ongoing debate regarding its impact on PRV operational stability. This paper presents comprehensive test data showing that restricting the lift of a direct spring‐operated relief device does not improve valve stability in vapor/gas service. The data further indicate that stability is not influenced by the required relief rate. While restricted lift reduces capacity, it does not alter the valve's dynamic characteristics. These findings are consistent with earlier work reporting negligible effects on blowdown and valve performance when lift is restricted. Data from over 1500 tests suggest that the reduction in lift can help mitigate some negative system effects caused by valve instability. These results underscore the importance of understanding the trade‐offs involved in applying restricted lift as a strategy to address PRV installation challenges without assuming improved stability.