Refer to the drawing of a water storage tank and level control system (see figure below) that have just been returned to service following replacement of the drain valve actuator.
Unfortunately, the original direct-acting actuator was mistakenly replaced with a reverse-acting actuator.
Given:
• The drain valve will now fail open if operating air pressure is lost.
• The level control system uses a direct-acting proportional-integral level controller with a setpoint of 15 feet.
• The level controller receives input from a direct-acting level sensor.
• The level controller is currently in manual control, with an operator maintaining the tank water level at 14 feet.
• Tank inlet and outlet flow rates are currently equal with the drain valve 50 percent open.
If the level controller is shifted to automatic control, the tank water level will…
A. increase and stabilize at 15 feet.
B. increase and stabilize slightly higher than 15 feet.
C. decrease until the tank nearly empties.
D. increase until the tank overflows.
Show Answer
Answer: C
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