The working principle of the J21W-250P DN20 needle valve is similar to that of the J23W and J23H needle valves, as follows:

When the handwheel is rotated clockwise, the valve stem rotates via the thread, causing the valve core to slowly press against the valve seat end face, thus sealing and achieving the closing function. When the handwheel is rotated counterclockwise, the valve core slowly moves away from the valve seat, achieving the opening function.

It should be noted that although the specific working principle of J21W-250P is not directly described in the search results, it can be inferred from the working principles of the J23W and J23H needle valves that the working principle of J21W-250P is similar. Furthermore, the J21W-250P uses a butt-welded connection, is suitable for a working temperature range of -29℃ to +538℃, has an engineering pressure ≤10000Psi, and is suitable for non-corrosive media such as water, oil, and gas, as well as corrosive media such as nitric acid and acetic acid.