Development of soft seal and experimental investigation of soft seated safety relief valves for cryogenic applications

Cryogenic propellant servicing of any advanced propulsion system before launch is very critical due to complex two phase flow during chilling, transient heat transfer, pressure and temperature management. Metal seated safety valves are generally prone to seat leakage due to surface roughness and even small degree of leak across seat is not acceptable for usage in cryogenic applications. In this study, the seat leakage across metal seated valves is mitigated by designing and developing a unique soft seal to replace metal seated safety valve seat. An experimental investigation is carried out to validate the developed soft-seated valve with ambient gases such as nitrogen and highly sensitive mass spectrometer test with gaseous helium. Liquid nitrogen tests are conducted to validate the performance of the developed soft seated valve at cryogenic temperatures. In addition, semi-empirical computations have been done based on contact surface characteristics and deformation analysis to assess seat leak rates with gaseous helium. The experimental test results indicated that the seat leak rate improved with increased cyclic operations compared to metal seated valves. The sealing characteristics improved to 0.61 x 10⁻⁶ mbar.l/sec from 4.72 x 10⁻⁵ mbar.l/sec at liquid nitrogen temperature. The computations of leak rate obtained by semi empirical computations was compared to that of experimental results and are found to be in close agreement. The results indicated the developed soft seated valve meets the leakage class requirements for cryogenic applications and can be applied to metal seated valve.