Seat tightness of pneumatic cryogenic control valve

Pneumatic cryogenic control valves (PCCV) are designed to meet the special requirements for the large cryogenic helium refrigeration system. Polychlorotrifluoroethylene (PCTFE) is adopted as the flat seal material of the valve seat. The leakage rates and compressive strain of the PCTFE gasket with different sealing stress are tested at both room temperature (293 K) and liquid nitrogen temperature (77 K). After 300 open/close cycles, the experimental results show that the sealing properties of the PCTFE gasket are improved. The leakage rates are about 10(-8) (293 K) and 10(-4) (77 K) Pa m(3) s(-1) respectively. Finally, the effects of working pressure on sealing characteristics are discussed. The working pressure has little effect on compressive strain but it has a great influence on leakage rate. The leakage rate is linear with the working pressure of inlet at room temperature, but at liquid nitrogen temperature the leakage rate is linear with the square of the working pressure.