control Valves are used to respond to signals from an external control device to control flow at variable levels between full or partial opening and closing, and to compare “set point” with “process variable”. The Control Valve often referred to as the “final control element”, is a critical part of any control loop that affects the whole process.
In the meantime, a relief valve is a valve that opens automatically to release excess pressure until the pressure is reduced to a level equal to or below a predetermined level.
Isolation valves are used to control the flow of process fluids from one pipe to another or redirect the flow to another path. This is usually done for maintenance purposes.
Finally, the regulator is simply a component that can pass through a predetermined amount of process flow regardless of the input pressure.