Fundamental of valves and their types...

Fundamental of valves and their types  Valves are mechanical devices. They are basic elements with which the flow of fluids and pressure within a system can be regulated. They are mainly used to control the direction of fluid flow as well regulate the amount fluid flowing through a particular system or a process. They perform any of the following functions. Starting and stopping or isolating fluid flow. This corresponds to on and off functions. Controlling or varying (throttling) the amount of fluid flow by change of direction or restriction. This corresponds to volume functions. Checking the flow or controlling the direction of fluid flow and preventing backflow. This corresponds to directional functions. Regulating downstream system or process pressure Relieving component or piping over pressure There are many valve designs and types that satisfy one or more of the functions identified above. A multitude of valve types and designs safely accommodate a wide variety of industrial applications. Regardless of type, all valves have the following basic parts: the body, bonnet, trim (internal elements), actuator, and packing. Valves work by creating a partial or complete obstruction in the flow of fluids. The formation of obstruction can be formed manually or by injecting automatic elements in the system. A manual valve is generally controlled by handles, pedals or levers. An automatic valve is generally driven by pressure changes (pneumatic valves), although there can be other versions as well, where they are driven by electrical signals (solenoid valves). Automatic valves are more common nowadays, except for operations which require human judgement. The regulation is accomplished by the varying resistance that the valve introduces into the system as the valve is stroked. As the valve modulates to the closed position the system pressure drop shifts to the valve and...