Split wedge and double disc gate valves must be installed:

The correct choice emphasizes that split wedge and double disc gate valves should be installed with the stem vertically up to ensure proper operation. This configuration prevents the potential for debris to accumulate in the valve body, which can affect its performance. When installed with the stem in the vertical position, both types of valves benefit from gravitational forces that help keep the sealing surfaces clean and reduce the risk of obstructions that could prevent the valve from closing tightly.

In addition, mounting the valve this way ensures that the mechanical components work effectively, allowing for reliable opening and closing actions. Proper alignment and orientation of the stem are crucial for achieving optimal sealing and extending the lifetime of these valves in a piping system.