What type of valves are permitted between the boiler and the water column?

The inclusion of O.S. and Y valves or stopcocks between the boiler and the water column is based on safety and functionality requirements in steam systems. These types of valves allow for isolation of the water column for maintenance while still enabling visibility and accessibility to the system. O.S. and Y valves provide a reliable means for throttling flow or completely shutting it off, and they are designed to support the operational needs of a water column by offering a clear and robust method for connecting and disconnecting the water column from the boiler.

Moreover, these valves are specifically constructed to withstand the pressure and temperature conditions found in boiler applications, ensuring effective operation without the risk of leaks or failures. They are designed with the capability for visual confirmation of the valve's position, which adds an additional layer of safety for operators, communicating whether the path is open or closed without needing to remove the valve from service.

In contrast, other types of valves listed, such as ball valves, gate valves, or check valves, may not offer the same level of reliability, appropriate operational capabilities, or safety features required in this particular application. They could introduce risks or functionality limitations that are not compatible with the critical role of the water column in boiler operation. Thus, the requirement for O