A valve assembly for a dunnage bag wherein in the valve body a valve diaphragm is mounted on a shaft and is supported by a mounting bar such that the valve diaphragm may be reciprocally moved from the closed position to the open position by a simple axial push on the valve shaft. The valve shaft is retained in the mounting bar in an orifice and the shaft diameter is enlarged at its end distant from the valve diaphragm so as to generate a frictional force fit or lock in the open position to facilitate the removal of air from the bag. The valve may be released form the friction lock by the air pressure of a recharged bag and/or by the manual movement of the valve diaphragm and shaft axially toward the open end of the valve assembly.