SAFETY VALVE

Safety valves are installed on pressure vessels, boilers etc. It is mostly used in Air, Gas, Steam systems.  It blows up continuously until the system pressure comes to normal operating pressure. The over pressure is released to the open atmosphere, a flare, or some safe place.

Relief valves are installed liquid systems. It opens instantly to relieve excessive pressure from piping and vessels.The extra pressure is released within system itself.

Relief valves are designed to protect personnel and equipment.

On a piping and instrument drawing these valves are often listed as PSVs or Pressure Safety Valves.

The two terms, relief valve and safety valve are used interchangeably.