When connecting two or more high-pressure boilers to a common steam heater, how many stop check valves are required near each boiler with a manhole opening?

In the scenario of connecting two or more high-pressure boilers to a common steam header, the requirement for the number of stop check valves is determined by the need to ensure safe operation and maintenance of the system. When a boiler has a manhole opening, it is essential to isolate the boiler from the common steam header for maintenance or repair work without affecting the operation of other boilers in the system.

Having two stop check valves near each boiler allows for a dual isolation point: one valve can be closed to isolate the boiler while the other remains open, ensuring that pressure does not drop unexpectedly in the system. This setup also helps to prevent backflow and allows for safer servicing of the boiler.

By employing two stop check valves near each boiler with a manhole opening, it ensures that both operational efficiency and safety protocols are adhered to, allowing for maintenance work to be conducted safely without the risk of steam escaping or pressure issues affecting the overall system.