Effect of valve lift and disk surface on two-phase critical flow at hot water relief valve

Critical flows through disk-type relief valves with different disk surfaces and lifts were investigated experimentally. The disk surfaces used were fouling brass with calcium scale, mirror-finished brass and clean Teflon. The critical flow rate obtained from the experiment was sufficiently higher than that calculated by the empirical correlation which is often used for calculation of valve capacity. From the comparison with data and a nonequilibrium homogeneous model, nonequilibrium effect was smallest in a valve using a disk of fouling brass and highest in a valve using a disk of mirror-finished brass. The nonequilibrium state was affected with flashing characteristics of valve disks and effects of lift were relatively small.