control valve

control valve

The most common final control element in the process control industries is the control valve. The control valve manipulates a flowing fluid, such as gas, steam, water or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point.
Generally speaking, the control valve assembly typically consists of the valve body, the internal trim parts, an actuator to provide the motive power to operate the valve, and a variety of additional valve accessories, which can include positioners, transducers, supply pressure regulators, manual operators, snubbers or limit switches. The ability of control valves to reduce process variability depends upon many factors. More than one isolated parameter must be considered. Research within the industry has found the particular design features of the final control element, including the valve, actuator and positioner, are very important in achieving good process control under dynamic conditions. Most importantly, the control valve assembly must be optimized or developed as a unit.

The control valve regulates the rate of fluid flow as the position of the valve plug or disk is changed by force from the actuator. To do this, the valve must:
1:Contain the fluid without external leakage;
2:Have adequate capacity for the intended service;
3:Be capable of withstanding the erosive,corrosive and temperature influences of the process;
4:Incorporate appropriate end connections to mate adjacent pipelines and actuator attachment means to permit transmission of actuator thrust to the valve plug stem or rotary shaft.