What is a control valve?

it explains what is a control valve, with an episode from VEGEteK.

1. VEGEteK - 009 What is a control valve?

2. It is an instrument that controls the flow of a fluid in a passage by varying the size of that passage. Main parts: 1- Body. 2- Actuator. 3- Positioner. Control valve

3. It increases or decreases fluid flow path size in order to control flow rate. Control system in the plant will send a control signal to operate the control valve to a status between fully open or fully close. There are feedback mechanisms to tell the current status of the control valve to the control system. Some control valves have a manual override option, which is useful when there is a problem in automatic position control. Usage

4. It is the part which the fluid will flow through, and it is the one which will move to change fluid passage size. Valve body Globe Butterfly Gate Diaphragm Ball

5. It is a mechanical assembly that directly controls the opening or closing of valve body. Main types: 1- Electrical: electric motor. 2 - Hydraulic: many types such as piston. 3- Pneumatic: piston or diaphragm. Valve actuator Hydraulic ( Piston) Pneumatic (Diaphragm) Electric

6. It is a mechanical assembly that directly controls the opening or closing of valve body. It is the most famous control valve actuator used in the industry. It has a diaphragm material that is being pushed by compressed air which causes valve movement from fully open to fully close depending to air supplied. Once air stops, a spring returns the diaphragm to its original state. This is for single acting actuators, but there are double acting ones which use 2 air supplies on the two sides of the diaphragm so it controls the opening and the closing of the valve. Diaphragm pneumatic actuator

7. It is the device that gives control signals for the actuator, and tells makes sure to move it to the desired position and maintains it there. It has an air supply input (ex. 6 bar) and a pneumatic control signal input (3-15 psi), with an air output which goes to the actuator. So it takes the 3-15 psi control signal and tries to produce air that matches it to the actuator. The 3-15 psi air signal is take from an I-to-P converter which in turns takes the 4-20mA control signal from the PLC (or any control system) and converts it to 3-15 psi. Some modern positioners have the I\P built-in, so the user feeds the 4-20mA signal to it directly. Positioner

8. Control valve connections with double acting actuator