Abstract: A check valve is placed in a conduit for pressurized fluids, and comprises a cylindrical external housing having inlet and outlet ends, a cylindrical internal spigot, and an elastomeric sleeve fitted over the spigot. It is sealed at the second end, and has a plurality of radially directed vent apertures along its length. The elastomeric sleeve is securely fitted to the internal spigot, in the region of the first, inlet end. The elastomeric sleeve has an internal diameter and an elastic memory such that it fits and adheres snugly to the outer periphery of the spigot, and its elasticity is overcome at a positive gauge pressure of between 5 and 20 psi so that pressurized fluid will flow from the vent apertures. Backflow of fluid at substantially zero or negative gauge pressure is precluded.