Final Answer:
No, the valve stem is not connected to the disc on an automatic non-return valve. Option A is the answer.
Step-by-step explanation:
In an automatic non-return valve, also known as a check valve, the valve stem is not directly connected to the disc. The valve operates based on the flow of fluid. When the fluid flows in the correct direction, it lifts the disc, allowing the flow to pass. However, when the flow tries to reverse, the disc is forced back into the closed position by the pressure, preventing backflow. The design is such that the valve stem and disc move independently, and their connection is not direct. This design ensures efficient and automatic operation of the check valve without relying on a mechanical linkage.
Option A is the answer.