Jawaharlal Nehru Technological University Hyderabad B.Tech III Year SURFACE PRODUCTION OPERATIONS Previous Question Paper (February/March - 2022 - R18)

A direct-acting actuator is a pneumatic or hydraulic device where the control signal pressure acts directly on a diaphragm or piston to oppose a spring force. The primary components include a diaphragm casing, a flexible diaphragm, a stem, a spring, and a valve plug.

In a direct-acting configuration, an increase in signal pressure pushes the diaphragm downward, compressing the spring and moving the valve stem to close (or open, depending on the valve body type) the valve. When the signal pressure is removed, the spring force returns the actuator to its original position.

Key labeled components in a sketch would be: 1) Air Signal Input (top of casing), 2) Diaphragm Casing, 3) Flexible Diaphragm, 4) Actuator Stem, 5) Spring (providing counter-force), and 6) Valve Plug/Seat interface at the bottom.

Level Control: Maintains the liquid level in a vessel within a specified range. It typically uses a level transmitter (e.g., displacer or radar) to send a signal to a controller, which adjusts an outlet valve to balance inflow and outflow. This is critical in separators to prevent gas carry-through or liquid carry-over.

Temperature Control: Regulates the thermal energy of a process fluid. A temperature sensor (e.g., RTD or thermocouple) monitors the fluid, and the controller adjusts the flow of a heating or cooling medium (such as steam or cooling water) through a heat exchanger to maintain the setpoint.

Flow Control: Manages the volumetric or mass flow rate of a fluid through a pipeline. It uses a flow meter (e.g., orifice plate or turbine meter) to measure the actual flow, comparing it against the desired setpoint. The controller then modulates a control valve to restrict or open the flow path, ensuring the process receives the correct amount of fluid regardless of upstream or downstream pressure fluctuations.