Control Valve

Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "set point" to a "process variable" whose value is provided by sensors that monitor changes in such conditions.

Control Valve Parts:-The Valves has Two Main Parts:1. Body Assembly2. Actuator Assembly

Body Assembly Parts: Body: The pressure retaining housing through which the service fluid flows. It has inlet and outlet connections, and houses the trim components.

Bonnet: The valve component which houses the guides and packing. It also seals one opening to the body.

Bonnet Flange: Flange that attaches the bonnet to the body.

Valve Trim: The internal elements of a valve are collectively referred to as a valves trim. The trim typically includes a disk, seat, stem, and sleeves needed to guide the fluid. A valves performance is determined by the disk and seat interface and the relation of the disk position to the seat. Because of the trim, basic motions and flow control are possible.

Seat/Seal ring: It provide the seating surface for the disk. To improve the wear-resistance of the seal rings, the surface is often hard-faced by welding and then machining the contact surface of the seal ring.

Stem: It connects the actuator and disk and is responsible for positioning the disk.Stem designs fall into four basic categories: Rising stem with outside screwRising stem with inside screw Non rising stem with inside screw Sliding stem.

Packing: It is used to prevent leakage and the space between the stem and the bonnet.

Packing Box: Internal bore of bonnet which contains guiding and packing.

Plug: Part that moves in and out of the seat ring to open and close the valve. It can also be used to characterize the flow.

All Gaskets: These are used in control valves to prevent leakage. around the seat ring, bonnet or pressure-balanced sleeve.

Actuator Assembly Parts Actuator: Device which develops sufficient thrust to open or close the valve. Common designs include piston, diaphragm, hydraulic, manual hand wheel and electro-hydraulic actuators. Lifting Ring: It is used for lifting the Valve.Adjusting Screw: Part used to compress the actuator spring.

Cylinder: Actuator part used for containing air pressure and enclosing the piston.Spring Button: The part that prevents movement of the actuator spring and permits the adjusting screw to compress the spring.Spring: In piston actuators, the part which provides force for fail-safe operation; in diaphragm actuators, the part that provides force to counteract air pressure from the opposing chamber.

Piston: Part used to separate two air chambers of piston actuator.

Actuator Stem: Part used to connect the valve plug with the piston actuator.

Yoke: A component which secures the actuator to the valve body.