Boilers in a battery equipped with what must have two main steam stop valves and a free-flowing drain between them?

The configuration of having two main steam stop valves and a free-flowing drain between them is crucial for ensuring safe and efficient operation in a battery of boilers. This system allows for isolation of individual boilers for maintenance and repair without disrupting the entire system's operation. When manhole openings are present, they provide access for inspection and maintenance of the boiler itself.

The positioning of stop valves on either side of these manholes ensures that if maintenance is required, the valves can be closed to prevent steam leaking into the work area, enhancing safety for personnel. The free-flowing drain is essential, as it allows any residual water or condensate that collects between the valves to be safely removed, eliminating potential hazards and maintaining proper boiler operation.

Thus, the presence of manhole openings necessitates this specific valve arrangement to comply with safety standards and operational protocols in boiler management.