What is control valve ?
Control valve is a power-operated device used to modify and control the fluid flow rate in a process system .They are widely used in various processes to control the flow , pressure , temperature and liquid level . The exact type of valves used will depend on the pipe size , working pressure, medium , working temperature and other process condition . Cost is aslo a enough factor to consider when making model selection .
There are two basic types of control valves
- Rotary motion valves having ball , butterfly or plug type closures
- Liner motion valves having globe , diaphragm or pinch type closures
Valves can be operated by manual or automated . If automated operated , there are rotary actuator and linear actuators , rotary actuator are usually for butterfly valve and ball valve , linear actuators are mainly for globe control valve .
Opening and closing of automated control valve are usually realized by pneumatic , electric or hydraulic actuators . Usually there is a modulating valve which can be set to any position between fully open and fully closed , valve positioners are used to make sure the required degree of opening of valve s .
An complete automated control valve contain three main parts
- Valve actuator , it is moved the valve’s modulating element, such as ball or butterfly
- Valve positioner, it is ensured the valve has reached the desired degree of opening , and overcomes friction and wearing
- Valve body , this part contact the measuring liquid , such as globe , butterfly , ball element