A pressure relief valve in a triple offset butterfly valve configuration. It has a body, pallet, pallet assembly and closure mechanism with a lever arm providing mechanical advantage upon a cam which aids in the closing of the valve. The valve relies upon a shear pin which can be machined to alter the opening pressure of the valve. The pallet is secured to the pallet assembly by a plurality of adjustment fasteners and retainer fasteners which can be adjusted to provide an effective seal on the valve. A valve seal has one or more layers of graphite and metal. A pallet seal is captured in a groove in the pallet which restricts radial movement of the pallet seal. The valve seal is captured between a retainer and the pallet seal.