Gate Valves for LNG & Cryogenic Service

A cryogenic valve extended bonnet serves a critical function: it keeps the packing gland at or above ambient temperature while the valve body is at cryogenic temperature (–162°C for LNG, –196°C for LN₂). This is necessary because: (1) most packing materials (PTFE, graphite, soft elastomers) lose their sealing ability at cryogenic temperatures — they become brittle and rigid at –160 to –196°C and cannot maintain the compression and sealing contact needed to prevent leakage; (2) if condensation or atmospheric moisture freezes on the stem packing, the stem may bind (freeze-seized); (3) extended bonnet design creates a thermal gradient along the bonnet length — the valve body is at –162°C, but by the time the cryogenic fluid vapour rises through the bonnet column, it warms and the packing area stays above –20°C where standard PTFE packing remains effective. BS 6364 specifies the minimum bonnet length as a function of the test/operating temperature and the valve nominal size. The bonnet length for an LNG (–162°C) gate valve is significantly longer than for a –46°C low-temperature service valve. Always specify the operating temperature on your enquiry for cryogenic valves — the bonnet length is determined by this temperature, and bonnet length affects the overall installed height of the valve (critical for platform/vessel space planning).