Key points of selection and maintenance (low-temperature special) 

 1. The key to selection: 

 ● Material matching medium: LNG choose 304L/316L, liquid hydrogen choose Inconel 625, sulfur-containing low-temperature medium choose Monel 400; 

 ● Temperature margin: the actual working temperature should be lower than the rated minimum temperature of the valve (such as -196℃ working conditions, choose the rated -200℃ valve); 

 ● Actuator adaptation: The electric actuator needs to be equipped with "low-temperature explosion-proof type" (Ex d IIB T4 Gb), and the pneumatic actuator needs to be equipped with a "low-temperature filter pressure reducing valve" (to prevent water freezing and blocking in compressed air). 

 2. Maintenance points: 

 ● Sudden cooling and sudden heating are prohibited: the valve must be pre-cooled (pre-cooling rate ≤5℃/min) before opening, and it needs to be slowly heated after closing to avoid deformation of parts; 

 ● Grease selection: "Low-temperature synthetic grease" (such as polytetrafluorovinyl grease, resistant to -200℃) should be used for stem lubrication, and ordinary grease (it will solidify at low temperature); 

 ● Regular sealing test: use the "helium mass spectrometer leak detector" to test the sealing performance of the bellows every 6 months (the leakage rate of LNG valve needs to be ≤1×10−9 Pa・m³/s); 

 ● Anti-icing measures: The outside of the valve should be "cold-preserved and insulated" (such as covering the polyurethane cold-preserving layer) to avoid the moisture in the air from freezing on the surface of the valve body, affecting the operation or corrosion of the valve body.