What is the difference between Relief Valve and Safety Valve?

Both relief valves and safety valve devices are high-performance pressure-sensitive safety apparatus designed to control or check the pressure inside the system or vessel by releasing the excessive pressure from the auxiliary passage out of the system. The fundamental difference between a safety and relief valve is that a relief valve relieves the stress by reducing the fluid back into the system, to the low-pressure side — an example would be the relief valve of a positive displacement pump.

A safety valve, on the other hand, relieves the pressure into the atmosphere out of the system. Relief valves are mainly used in a fluid. Safety valves are mainly used for the release of vapor or steam up into the atmosphere.