The seat and disc of which valve must be removable without removing the entire valve from the pipeline?

The check valve is designed to allow fluid to flow in only one direction and prevent backflow. One of the key features of certain types of check valves, particularly swing check valves, is that the seat and disc can be removed for maintenance or replacement without requiring the entire valve to be disconnected from the pipeline. This design is crucial for minimizing downtime and costs associated with valve maintenance, as it allows for quick access to the internal components.

In contrast, other types of valves, like gate and globe valves, do not typically allow for the removal of internal parts like the seat and disc without taking the entire valve out of the pipeline. A gate valve requires complete removal to access the gate and its seating surfaces, while a globe valve, which is primarily used for flow regulation, also necessitates complete removal from the pipeline for any internal maintenance. Plug valves operate differently and involve disassembly of the valve body for internal access, making them less efficient for quick maintenance. Therefore, check valves are specifically designed for ease of maintenance without the necessity of removing the whole valve from the pipeline.