Diaphragm pump with at least two diaphragms

A diaphragm pump (1) comprising a pump case (2) having a pump chamber (13) at one end thereof including an inlet port (11) and an outlet port (12) adapted for connection to respective inlet and outlet valves, a connecting rod (8) with at least two diaphragms thereon, and an eccentric drive (7) for driving the connecting rod, wherein a working diaphragm (16) closes the pump chamber (13) and has a deformable annular zone (24), said working diaphragm (16) being essentially generally flat and level in an undeformed condition, and at least one additional diaphragm (26) being arranged between the working diaphragm (16) and the eccentric drive (7) and having a deformable annular zone (30), whereby an at least essentially closed diaphragm interspace (29) is formed between the two diaphragms (16, 26) and is laterally defined by the pump case (2), and wherein the deformable annular zone (30) of the additional diaphragm (26) has a radial expanse wider than the deformable annular zone (24) of the working diaphragm (16), and the deformable annular zone (30) of the additional diaphragm (26) has a channel-like convexity (31) which in an undeformed condition of the diaphragm points toward the eccentric drive (7), wherein the additional diaphragm (26) has on a side thereof facing the eccentric drive 17) holding-down ribs (33), said holding-down ribs being connected to a connecting-rod arm (28) of the eccentric drive (7) by way of a hollow shank (34) incorporated in said diaphragm (26) and adapted to the connecting-rod arm (28), and said holding-down ribs being oriented toward a longitudinal axis of the connecting-rod arm (28).