Structural and Technical Features of Cryogenic Valves

Optimization of Valve Body and Stem Structure

Special attention is given to the wall thickness and diameter of the valve body and stem during the design of cryogenic valves to ensure strength and reliability under extreme conditions:
Minimum Wall Thickness Design: The wall thickness of the valve body and bonnet is not determined by the ASME B16.34 standard but is selected based on the specific valve type and application:
Gate Valves: The wall thickness of the valve body and bonnet must not be less than the requirements of the API 600 standard.
Globe Valves: The wall thickness of the valve body should meet the minimum requirements of the BS 1873 standard.
Check Valves: The minimum wall thickness should comply with the BS 1868 standard.
Stem Diameter: The stem diameter must be designed to meet the requirements of API 600 or BS 1873 standards to ensure sufficient bending strength and wear resistance under cryogenic conditions, coping with the load and wear caused by frequent operation.
Packing Box, Packing, and Gasket

The design of the packing box and packing is critical to the sealing performance of cryogenic valves:
Packing Box Position Design: The packing box is usually placed at the top of the extended bonnet to avoid direct contact with the cryogenic section, allowing the packing to operate at a relatively higher temperature. This design improves sealing effectiveness and reduces packing wear.
Double Packing Structure: For cryogenic valves with a nominal diameter of ≥DN300, a double packing structure with an intermediate metal isolating ring is recommended to enhance sealing and service life.
Packing Material Selection: Flexible graphite packing with 304 stainless steel wire braiding or lip-type PTFE packing (suitable for media temperatures above -73°C) is typically used to maintain good sealing performance in cryogenic environments.