The guard valves upstream of the turbine throttle valves serve primarily to do what during a fault?

• A. Stop steam flow to the turbine.
• B. Increase steam flow.
• C. Vent steam to atmosphere.
• D. Cool the turbine.

Answer: (A)

Guard valves are fast-acting isolation valves placed upstream of the turbine throttle valves. In a fault, they close quickly to stop any further steam from reaching the turbine. This isolation protects the turbine from damage due to excessive pressure, thermal shocks, or abnormal conditions, and allows the system to depressurize safely. They aren’t used to vent steam to atmosphere, cool the turbine, or increase steam flow, which is why stopping the steam supply is the correct function.