 The relief valve is designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits.When the set pressure is exceeded, the relief valve becomes the "path of least resistance" as the valve is forced open and a portion of the fluid is diverted through the auxiliary route.The diverted fluid (liquid, gas or liquid–gas mixture) is usually routed through a piping system known as a "flare header" or "relief header" to a central, elevated gas flare where it is usually burned and the resulting combustion gases are released to the atmosphere.