Relief Valves are designed to let off pressure in any situation where a system becomes overpressurized. Relief valves are designed to control pressure in a system, most often in fluid or compressed air systems. They open gradually, allowing the system to return to the preset pressure level. When that level is reached, the valve shuts. A Safety Relief Valve is designed to immediately release pressure in the event of an emergency or system failure. They open immediately and completely to avoid a disaster, rather than to control the pressure of a system.