If a boiler in battery has a tube rupture, the automatic nonreturn valve will _______.

• A. Prevent steam flow from the steam header into the ruptured boiler
• B. Open to relieve pressure
• C. Shut off the fuel supply
• D. Isolate the feedwater line

Answer: (A)

The automatic nonreturn valve in a boiler battery acts as a one-way gate between each boiler and the common steam header. Its job is to let steam flow from a boiler into the header but prevent any flow back from the header into that boiler. If a tube rupture occurs, pressure in the header could push steam back toward the ruptured boiler, potentially causing more damage or dangerous conditions. The nonreturn valve stops that reverse flow, isolating the ruptured boiler from the header while steam continues to be supplied by the other boilers.

This device is not meant to relieve pressure, shut off the fuel supply, or isolate the feedwater line, which are handled by other safety systems and valves.