Final answer:
When two stop valves are used on a steam outlet line, it is good practice to have one valve that is slow opening. The other valve should be an automatic non-return valve, also known as a check valve.
Step-by-step explanation:
When two stop valves are used on a steam outlet line, it is good practice to have one valve that is slow opening. This is because the slow opening valve allows for a gradual increase in steam flow, which helps prevent sudden pressure surges that could damage the system or equipment.
The other valve should be an automatic non-return valve, also known as a check valve. This valve allows steam to flow in one direction only and prevents backflow, ensuring that the steam flows in the intended direction and doesn't mix with the condensed water or other fluids in the system.
Having these two types of valves on a steam outlet line helps maintain system integrity and safety, as well as optimize the performance and efficiency of the steam distribution system.