Why is the exhaust valve open before steam supply?

• A. Because the exhaust pipe is not rated for the amount of pressure
• B. To prevent overheating by heating the exhaust
• C. To maximize steam entering the turbine
• D. To vent air from the boiler

Answer: (A)

Opening the exhaust valve before steam supply serves as a pressure relief during startup. If steam is admitted while the exhaust path is closed, the exhaust line and related components could experience a pressure surge beyond what they’re designed to handle. Keeping the exhaust open provides a controlled route for steam (and air) to escape, preventing overpressure and protecting the turbine and piping until the system reaches a steady running condition. This isn’t about heating the exhaust, maximizing steam entry, or venting boiler air—the practical purpose is to avoid overpressurizing the exhaust path.