Introduction
The motor operated valves (MOV) is an important element of the plant and pipe system. These valves are generally large and are used for different applications such as pump discharge, etc. The control valves operated by motor are often called on / off valves since the motors serve to open or completely close the valves in the pipes. For example, cooling water lines, process piping where fluid control is not required, motor operated valves can be used to completely allow or completely stop the flow of fluid. These valves are not used for throttling purposes since they mainly serve On-Off service applications.
The valves operated by motor can be of various types, e.g. Gate / Ball / Butterfly etc. with actuator control. The design of engines and valves may be different. An electric motor is mounted on the valve and geared to the valve stem so that when the engine is running, the valve will open or close. For this MOV, a motor operated with actuator control is required from the local panel or from the control room. There is a requirement for coordination between the pipeline, electrical, instrumentation, process and supplier engineers for the design and acquisition of such motor-operated valves.
Applications of motor operated valves
• Whenever frequent operation is required.
• Valves located in remote, inaccessible or dangerous places.
The motorized control valve / motor operated valves are generally for full opening and full closing applications. However, there are places where they are also used for position control.
Types of valves operated by motor
The motorized control valve can be classified into three types. However, it must be taken into account that the main application of motorized valves is for flow control and flow isolation.
• Opening / closing valves: used to automate manual open-closing valves. Some examples are pump discharge / suction valves, boiler feed water isolation valves, drum vent valves, product line valves, etc.
• Inching valves:used were some degree of control. For example, a gradual opening and closing is required, applications include reflux lines, boiler start vent, boiler IBD valves, boiler main steam valves, etc.
• Precision flow valves: this is a precision inching valve, in inching valve the motor operates in steps configured in the controller, e.g. 5%, 10% opening steps. In precision flow valves, continuous control is enabled by the use of adequate feedback from the field to the controller, which is not usually found in other engine operated valves. An example is the steam injection valve / water injection valves used in GT for Nox control