Sliding-stem valves include globe valves, angle valves, and axial flow valves. Of all the control valve types, the sliding-stem, globe style valve is the most common. As shown in Figure , the major components of a sliding-stem, globe style valve include the valve body, bonnet, trim, gaskets, and packing.
- A sliding stem valve with a diaphragm actuator and digital positioner should have a precision (deadband, resolution, and threshold sensitivity) of less than 0.2%. Even the best rotary valves usually have a precision that is twice as large
- A sliding stem valve has a direct connection between the actuator shaft and the internal flow element trim (e.g., plug). The motion is linear and direct. There is no backlash from shaft connections, translation from linear to rotary motion, linkages, or rotary element seals (e.g., ball and butterfly seals).
- Sliding stem valves offer a better installed characteristic than that of rotary valves. The installed characteristic for rotary valves tends to become too flat at upper valve positions (i.e., more open); valve gain becomes too low. Sliding stem valves also offer more choices for inherent trim characteristics.