In what positions will the air-operated...

In what positions will the air-operated regulating valves, shown in the illustration, be in when the steam in the gland seal supply line is excessive? See illustration SE-0020.

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🔍 Key Concepts

• Review how an air-operated diaphragm control valve responds to increasing control (regulating) air pressure: does more air tend to open or close each valve in this sketch? • Think about the different functions of the supply pressure control valve (on the left) versus the excess steam unloading valve (on the right). One maintains set pressure to the glands; the other protects against overpressure by dumping steam. • Note where the controlled pressure sensing line from the gland seal header goes back to each pilot controller, and how a rise in that sensed pressure would change the pilot air output to each valve.

💭 Think About

• If the pressure in the gland seal line rises above the setpoint, what correction is needed from the supply side? More steam into the header, or less? How would that affect the position of the supply valve? • At the same time, what should a protection/unloading valve do when pressure is too high: admit more steam to the glands or send excess steam somewhere else (e.g., condenser)? How would that affect its valve position? • Compare the direction of action of the two valve actuators: which one is drawn to fail-closed and which to fail-open, and why would that make sense for safety and gland sealing needs?

✅ Before You Answer

• Be clear which valve body in the illustration is the supply pressure control valve and which is the excess steam unloading valve before deciding. • Trace the operating air path from each pilot controller to each valve actuator and think through what happens to that air signal when sensed pressure is above setpoint. • Verify that your final choice is consistent with the basic control idea: high gland seal pressure should result in reduced steam supply to the header and a path for excess steam to be relieved.

🔍 Key Concepts

💭 Think About

✅ Before You Answer