In a high-pressure boiler installation, where must shutoff valves be located?

• A. In the supply line only
• B. In the return line only
• C. In both the supply and return lines
• D. In the fuel line

Answer: (C)

Isolating a high‑pressure boiler safely requires stopping flow on both sides of the boiler. Placing shutoff valves in both the supply and return lines lets you completely isolate the boiler from the piping system for service, testing, or emergencies. If you only close the valve in the supply line, the return line can still circulate water back to the boiler, keeping it pressurized and hot. If only the return line is shut, the supply can still feed the boiler. A single valve cannot fully de-energize the boiler and make it safe to work on. The fuel shutoff stops fuel, but it does not prevent water/steam flow, so valves on both lines are needed to ensure complete isolation.