Abstract: A pressure relief valve includes a housing defining an internal valve chamber. A valve seat is positioned within the chamber, and a valve pallet is reciprocally mounted within the chamber to engage the seat in a valve closed mode. A spring is mounted within the housing to bias the valve pallet into engagement with the valve seat. A spring retainer is threaded through an aperture in the housing and extends into the valve chamber. The spring is located within the retainer. A desired set pressure to be imposed upon the valve pallet is provided by threading the retainer relative to the housing thereby compressing the spring. To lock the retainer relative to the housing, an annular lock member is threaded onto the outside of the retainer. Once the desired set pressure is attained, the lock member is threaded on the retainer until it abuts the housing. The lock member includes first and second ends spaced apart to define a gap.