What is a control valve?
A control valve is a final control element used to control fluid flow by varying the size of fluid passage in response to the signals received from controllers.
Control valves are used to control condition such as flow, level, pressure , temperature.
What are the main parts of a control valve?
Basically there are two main sections for valve, the Body and the Actuators
Diaphragm, Actuator steam, yoke, actuator spring, Travel indicator comes under the Actuator part.
Valve body, valve plug, seat ring, guide ring comes under Body part.
What is a valve Cv ?
Valve Cv is the capacity of the valve. In other words, number of gallons of water per minute passing through the valve in the full option condition with 1PSI pressure drop across the valve at 15 degree temperature.
What are actuators? what are the types of actuators?
Actuators are the driving unit of a valve, which consist of diaphragm and piston that operates the valve stem by receiving the control signal.
Actuators are divided into three based on the source of energy used for the movement of the valve stem .
- Pneumatic actuators : Compressed air ( 3-15 psi) is used for actuation of diaphragm .
- Electric actuators : Electric actuator use electric currents.
- Hydraulic actuators : Hydraulic fluids are used used for actuation.
What is valve glanding?
A valve glanding prevents the process fluid from coming out through the valve stem. Glanding is the part of the valve body.
commonly used gland packing are Teflon, Graphite, Asbestos etc,.
What is a valve positioner ?
A valve positioner relates the input signal and the valve position, and will provide any output pressure to the actuator to satisfy this relationship, according to the requirements of the valve, and two ensure actuator stem take a position proportional to the input signal.
What is an Over sized control valve?
If a minimum signal to the valve or minimum opening of the valve brings the process set-point rapidly then the valve is Over sized for the porpose
How Over sizing can be fixed?
By replacing the valve or changing the valve trim to reduced size.