In a non-rising stem gate valve, the threaded section of the stem and the stem nut are located inside the valve body and remain in contact with the medium; the stem undergoes only rotational movement without vertical displacement. Also known as a rotating-stem or non-rising wedge gate valve, this device controls fluid flow through stem rotation. It utilizes a design where the trapezoidal threads at the base of the stem engage with the gate's guide slots, converting rotational motion into the vertical lifting of the gate; in the fully open position, the gate rises to a height equal to the nominal bore diameter. The key distinction from rising-stem gate valves is that the stem rotates without shifting position and the threaded shaft remains enclosed, making it suitable for installations with limited space. The valve body is typically constructed from ductile iron or cast steel, while the stem employs 2Cr13 stainless steel paired with a high-hardness nut assembly; operation follows the clockwise-to-close principle, with torque limited to 240 N·m.
The primary advantage of this design is that the stem does not rise during opening, requiring minimal installation space; consequently, it is frequently used for large-bore applications or in space-constrained environments, such as underground piping or compact equipment assemblies. Its disadvantages include the susceptibility of stem threads and related components to corrosion from the medium and the difficulty of lubrication; furthermore, unlike rising-stem valves, the degree of opening cannot be visually gauged by the stem's extension, necessitating the installation of an opening indicator.
