US Patent 7748398 Pressure relief valve for a container

A pressure relief valve for a container having a liner therein for holding food products includes a hollow body incorporated into a lid of the container and extends inwardly therefrom. A cutter member is mounted in an opening at an outer end of the body and has a knife extending inwardly through the valve body. A piston is slidably connected to the body and has an opening therein for receiving the knife and a compression spring is mounted around the knife and positioned between a top of the cutter and a bottom of the piston to bias the piston inwardly away from the wall. Pressure buildup in the liner causes the liner to expand and push the piston outwardly towards the lid to expose the knife which then punctures the liner and relieves the pressure therein and allows a product to be discharged from the container through the valve.