36c of poppet valve member 36 has ceased which pressure may be mechanically exerted by the top end of extension rod 47 or dynamically by compressed air impinging on tip 36c and the underside of accordion wall 50c the latter will return to its initial uncompressed condition as shown in fig8 and will pull the disk shaped head portion 36b with its annular peripheral sealing ring 37 into sealing contact with the valve seat formed by the flat annular gasket portion 50a of valve 50 accordion wall 50c has a central opening 50d for receiving the valve stem portion 36a therein and cup portion 50b has a lateral opening 50e for the flow of from the product bag 38 when valve 50 is open fig9 shows a dispenser similar to that of the preceding embodiment of fig8 but with a somewhat different product flow control valve structure in most cases this structure will be preferred because of its simple rugged nature the accordion wall 50c of product control valve 50 in the preceding embodiment is replaced by a flexible compressible but less elastic bottle neck shaped membrane 50f which is unperforated and encloses the valve stem tip 36c the latter being pressed into a recess 50g in the inside wall of membrane 50f a further simplification resides in the replacement of annular sealing ring 37 by a frustoconically beveled lower rim 37a or disk shaped head portion 36b of poppet valve member 36 in the closed position this beveled.