Disclosed herein is a positive pressure relief valve having a valve assembly, a trigger mechanism, an inlet manual override knob, and an outlet manual override knob. The valve assembly may comprises a valve throat and a main piston positioned at least partially within the valve throat, the main piston configured to selectively open and close the valve throat as a function of a pressure at the inlet to the valve assembly. The valve assembly may comprise a set of throat inserts within the valve throat. The trigger mechanism serves to quickly pressurize the main piston's diaphragm. The trigger mechanism may be positioned in a trigger mechanism housing at the outlet end of the valve assembly. The inlet and outlet manual override knob may be coupled to the main piston and configured to pull or push the main piston, thereby displacing the main piston to open the valve assembly.