Control valve is used to control flow at varying degrees between fully or partially opening or closing in response to a signal from an external control device and compare a "setpoint" to a "process variable". The control valve, usually mentioned as “the final control element,” is a critical part of any control loop that affects the entire process.
Safety Valve is valve that has opening that will open automatically to relieve excessive pressure until its pressure is reduced to a pressure equal to or below that of the predetermined level.
Isolation valve is used to control the flow of process liquid from one pipeline to another or to redirect the flow to a different path. This is usually done for maintenance purpose.
Lastly, regulator is just a component that allows through a predefined volume of process flow irrespective of the incoming pressure.