For the GWC USA company, a control valve is a very well known and popular valve since it is used to control fluid flow by varying the sixe of the flow passage that is directed by a signal from a controller. This is why it is called the control valve since the controller is able to set the size of the flow passage. The pressure, temperature and the liquid level is what is controlled by the controller which is unique compared to any other valves.
The operation of this valve is the opening or closing of automatic control valves is usually by a electric, pneumatic actuators or hydraulic. When it comes to the automatic control valves, there are three main parts including the valve actuator which is able to move the valve’s modulating element, the valve positioner which works to ensue the valve has reached the degree of opening and it controls problems like friction and wear of the valve, then there is the valve body which is the modulating element itself, it is a plug, globe, ball or butterfly and it is contained.
For the control action, this can be an air-operated valve and there are two control actions you can use which are the air or current to open which the flow restriction decreased due to the increase control signal valve and then there us the air or current to close and this is when the flow restriction increases the control signal valve. There is also the air or control signal failure to close which is when there is a failure of compressed air to the actuator and the valve closes, and there is the air or control signal failure to open which is when there is failure to compressed air to the actuator actually opens under the pressure of the backup power.