When a high pressure boiler plant only has one boiler which statement would be true?

In a high-pressure boiler plant with only one boiler, the need for certain equipment is dictated by the operational and safety requirements of that boiler system. When there's a single boiler at work, an automatic non-return valve is typically not necessary. This is because a non-return valve, which prevents backflow, is often used in systems with multiple boilers or other components where flow direction is a concern to maintain safety and efficiency.

In a single boiler setup, the risk of backflow into the boiler is minimal, since there are no other sources or paths for reversed flow. The boiler itself is designed to operate under specific pressure and flow conditions, and when it is the only one in the system, the flow dynamics are simpler. Thus, the absence of a non-return valve does not compromise the system's safety or performance in this context.

The other options present equipment that either does not fit the operational needs of a single-boiler system or contradicts safety practices. For instance, a manual valve’s installation isn't typically required just because there is one boiler, and removing a safety valve would be unsafe and against code. In a properly designed system, safety valves must always remain installed to protect against overpressure conditions.