Why Are Control Valves Used?
Process plants consist of a number of control loops that are networked together to make a product ready to be offered for sale. Each control loop is designed to keep some significant process variable such as temperature, pressure, level, and flow, within a desired operating range to make sure the quality of the end product is not compromised. Each loop receives and creates disturbances internally, which adversely affect the process variable. In addition to this, interaction from other loops in the network creates disturbances that impact the process variable.
To reduce the effect of these disturbances, transmitters and sensors gather data about the process variable and its relationship to a desired set point. This data is processed by a controller to decide what must be done to get the process variable back to its original position.
Functions of a Control Valve:
There are a number of important functions that a control valve must fulfill to function properly. These functions include:
- They should fit within the rest of the control assembly.
- There should not be any external leakage.
- They should be resistant to media characteristics.
- They should have adequate capacity for the system media.
A disruption in the control system activates control valves. When a control system is disturbed, the valve manipulates the flowing media to compensate, and keeps the process variable close to the desired set point.
Principles of Operation
Control valves are the most common final control element in the process control industry. A control valve manipulates a flowing fluid, such as steam, water, gas, or chemical compounds, to compensate for the load disturbance. This helps in keeping the process variable as close to the desired set point as possible.