A valve plunger movable through an opening in the wall of the product container, cooperates with a valve housing which receives product from the container and with a propellant cartridge carried by such housing within the container. Discharge of the propellant through a passage in the plunger in aspirating relation to a passage from the valve housing induces a flow of product which is discharged together with the propellant into the atmosphere. A resiliently deformable annular valve within the product container is clamped between the valve housing and the container wall with its inner periphery in sealing engagement with the valve plunger to prevent leakage of product externally of the plunger through the opening in which the plunger moves. The outer peripheral portion of the valve projects outwardly from the housing and across an annular channel encircling the housing to sealingly engage an annular valve seat concentric with the annular channel. The channel communicates with the atmosphere through the aforesaid opening and atmospheric air entering said channel may unseat the valve to permit influx of atmospheric air into the container for pressure equalizing purposes. One or more grooves or passages opening from the channel through the valve seat at locations normally covered by the valve, are uncovered in the event the valve is deformed by an internal superatmospheric pressure so as to be depressed into the annular channel and rocked about the inner edge of the valve seat whereby to uncover the vent passage.