Air vessel for compensating flow rate fluctuations in pressure lines of pumps and the like

The air vessel for compensating flow rate fluctuations in pressure lines of pumps and the like, especially of oscillating positive displacement pumps, has a tubular membrane (4) through which the flow medium (3) flows, a reservoir fluid (5), which surrounds the tubular membrane (4), in a housing (6) which contains the tubular membrane, and a feeler valve (11), arranged on the outer face of the tubular membrane, in the reservoir fluid (5), and a pressure vessel (7) holding the reservoir fluid. In this design and arrangement of the air vessel, the flow medium passes through the vessel in a straight line. Preferably, the tubular membrane is a double tube, so that the flow medium cannot come into contact with the reservoir fluid for the pressure vessel.