It is necessary for automatic process control system. It can be used either for controlling level, flow rate, temperature, pressure etc. The selection of control valve involves its operation mechanism, process conditions as well as requirements. It can be manual or power operated. The main parts of a control valve are actuator and body. The signals from the process are received by the actuator and accordingly it closes or opens the valve. Control valves can be single plug balanced globe type or double plug balanced globe type or having diaphragm or butterfly design. Single plug type valve gives better sealing. Pneumatic diaphragm and spring actuator is most commonly used. Control valve can have size ranging from 3mm to 500 mm and can be used for pressures up to 4000 kg/cm2 and temperatures-250°C to 800°C. Material of construction for control valve can be cast iron, carbon steel, stainless steel, Monel, nickel alloys, Hastelloy and even plastic also.