Valves

Valves are the components in a fluid flow or pressure system that regulate either the flow or the pressure of the fluid. This duty may involve stopping and starting flow, manipulating flow rate, diverting flow, preventing back flow, controlling pressure, or relieving pressure. 

Depending on processing systems valves are encountered in different sizes, shapes and types. However, all valves possess three main characteristics:

• An inlet and outlet point, otherwise known as a port, through which gas or liquid can enter and leave the valve
• A movable part which is applied to open/close the passage way through the valve
• A passageway through the valve through which the product flows from one side of the valve to the other side 

Despite of type, all valves have the same set of common parts illustrated in Figure 1. All the shown parts are given in the following.
 

Figure 1. Valve