Process flow diagram is a diagram, which is commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations. Typically, process flow diagrams of a single unit process will include the following process piping, major equipment items, control valves and other major valves, connections with other systems, major bypass and recirculation streams.