Refer to the drawing of a 30-foot water storage tank and its level control system (see figure below).
The level control system has 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 air pressure is lost to its actuator.
• The level control system uses a direct-acting level sensor and a direct-acting
proportional-integral level controller with a setpoint of 15 feet.
• The tank water level is stable at 16 feet with the drain valve 50 percent open.
• The level controller is in Manual control.
If the level controller is shifted to Automatic control, the tank water level will…
A. increase until the tank overflows.
B. decrease until the tank almost completely empties.
C. initially increase, and then decrease and stabilize at 15 feet.
D. initially decrease, and then increase and stabilize at 15 feet.
Show Answer
Answer: A
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