How many stop valves are required between boilers having a manhole opening when connected to a common steam header?

The requirement of two stop valves between boilers having a manhole opening when connected to a common steam header is primarily a safety and operational consideration. Having two stop valves ensures that each boiler can be isolated independently from the common steam header. This is vital for maintenance, as it allows for safe access to the boiler without interrupting the operation of the other boiler connected to the same header.

In addition, using two stop valves provides a reliable means to prevent backflow and ensure that steam can be effectively controlled and monitored from each boiler. The installation of two valves also complies with industry best practices and regulations, which are designed to enhance safety by creating a barrier that can be closed off in case of maintenance or in the event of a safety issue.

The number of stop valves is significant because if only one were installed, that single valve would be responsible for isolating the entire system, which could lead to operational risks and complications during maintenance. This reinforces the necessity of having double valves in such configurations to maintain the integrity and safety of the entire system.