What Is a Control Valve?
A control valve regulates process conditions such as flow rate, pressure, temperature and liquid level by changing the size of the flow passage in response to a signal from a controller. It can operate fully open or fully closed, or hold any intermediate position so that the medium passes at the required rate.
Because control valves respond automatically to signals, the process does not need to be monitored and adjusted by hand. They work with a wide range of media, including water, hot water, steam, gas and chemical fluids, and are the final control element in most process control loops.
Working Principle
In a control loop, sensors and transmitters measure a process variable, for example pressure or temperature. The controller compares this measured value with the set point and sends a corrective signal to the valve actuator. The actuator, which can be pneumatic, electric or hydraulic, moves the valve plug or disc to open or close the valve fully or partially. When a deviation from the set point is detected, the valve quickly brings the process variable back to the desired value, keeping the process stable.
Control Valve Types
- Level control valve: a simple, easy-to-install valve that keeps the fluid level within an adjustable range and acts when the level moves outside it.
- Proportional control valve: adjusts flow, pressure and temperature precisely and can also change the direction of flow; suitable for hot oil, hot water and acidic or corrosive media, with high sealing performance.
- Pneumatic control valve: operated by a pneumatic actuator for opening, closing and precise flow regulation between minimum and maximum values.
- Pressure control valve: maintains the required downstream pressure regardless of flow changes; easy to maintain.
- Automatic control valve: uses line pressure and pilot valves to open, close and regulate the flow without external power.
- Steam control valve: controls steam flow and temperature in steam systems, available with different materials and actuators.
Technical Range
Luna Flow Control supplies proportional (modulating) and on-off control valves in nominal sizes from DN 15 to DN 600, with flanged, SW/BW or threaded connections and pneumatic or electric actuators, for operating temperatures up to +550 °C.
What Does a Control Valve Do?
Process variables that rise above or fall below their limits can cause serious problems in a facility. The control valve keeps gas, steam, water and chemical flows close to their set points and corrects disturbances automatically, making it one of the most important elements of any control loop.
Application Areas
- Steam and heating systems
- Water and hot water distribution
- Chemical and petrochemical processes
- Oil and gas installations
- Tank level control
Advantages
- Accurate, automatic control of pressure, flow, temperature and level
- Reduced need for manual supervision
- High sealing performance for safe operation
- Long service life when correctly sized and installed
Selection Tips
Size a control valve according to the required flow range and pressure drop, not only the pipe size. Define the medium, operating pressure and temperature, the required control characteristic (proportional or on-off) and the available actuator energy (compressed air or electricity) before selection.
