according to the system of fig1 gas from a source 1 ( either ( a ) stored in a cylinder , ( b ) a hybrid system of stored gas and gas produced from a pyrotechnic powder or ( 3 ) gas produced only from a burning powder ) is directed into a manifold 3 through a passageway 2 . in many applications , a smaller bag 4 referred to hereafter in the specific embodiment illustrated as a knee bag , but not limited thereto , located within the primary inflatible gab 5 is inflated first , in order to ( a ) position the occupant , ( b ) provide restraint to said occupant and especially to his lower torso and legs , ( c ) capture the first hot gasses in an interior bag , and / or ( d ) provide for energy absorption . inflating gas enters the smaller bag 4 from the manifold through opening 6 which is covered by flexible flapper valve cover 7 connected to the outside surface of the manifold 3 by suitable means such as use of adhesive at the top 8 thereof , as in the embodiment shown . the flapper valve cover may be made of rubber , flexible nylon , other flexible plastic material , or of other suitable flexible material as desired . in operation , on the first flow of gas from the gas source through the manifold , flexible flapper valve 7 opens under the pressure differential to allow the gas to fill the unexpanded smaller bag 4 . when said bag is filled , however , and a pressure balance is thus substantially achieved , the flapper valve 7 returns to its normal position against the outside surface of the manifold and ( 2 ) further flow into the smaller bag estimated , forcing flow into the primary bag 5 through other entry ports . in fig2 the flexible flapper valve 7 is shown in its normal position against the outer surface of the manifold 3 . the provision of flexibility for the flapper valve allows for relatively inexpensive construction and ease of attachment , as compared to a rigid metal flap , for example , and , most important , allows for effective seal of the cover against the outer surface of the manifold 3 , without , for example , machined indenture provisions on said surface of the manifold to receive said flap and allow for a seal .