What's the difference between a Pressure Regulating Valve, Pressure Release Valve, Pressure Relieving Valve, and Pressure Relief Valve? Known as PRV.

Pressure Regulating is to maintain the pressure of a device to a specified value through all operation circumstances.

Pressure relieve valves are valves that will vent a device at a preset pressure. They are typically safety devices.

Pressure release valves are manual valves which releases the device pressure on demand.

1. The pressure regulating valve : it cuts the flow of the gas or the liquid to the adjusted pressure, it is also pressure reducing valve.
2. The pressure release valve, pressure relieving valve, pressure relief valve : it protects a pressurized system from over pressures. the excess of liquid will flow out of the system.

I agree with Mr .Samer answer ...thanks

I AGREE WITH MR SAMER ANSWER 

Beautiful Answer Given by Mr. Samer Draidi No need to add more.

first of all am discus about pressure regulting valve isregulerly regulate prssure  it mean it is periodic.2nd is release the pressure to the valve.it is the different typeof the valve discussed about here.when we relief the pressure then it is called prv.

Basically its three types of valves which cover your Question.

1. Pressure Regulating Valve:

Its application is to reduce the pressure downstream to the valve from the higher supply pressure to the lower operating pressure in a system.

2. Pressure Release Valves:

Typical application cover the release of pressure from the piping to do maintenance after isolation. It just release the pressure and make piping free of water.

3. Pressure Relief Valves:

These valves are usually spring or Diaphragm type valves which are given a set point of pressure, and if the pressure in piping increase to that point, the valve will open to protect the piping.

I agree with all answers above