Patent ID: 7445028

Claim:
A check valve comprising: a flexible tubular valve member extending longitudinally between an inlet and a longitudinally opposite outlet, the flexible tubular valve member having a longitudinal passage for conducting a fluid from the inlet to the outlet, and a valve wall extending longitudinally between the inlet and the outlet and circumferentially around the passage; the valve wall including a bill extending longitudinally along the valve wall and terminating at a bill end contiguous with the outlet, the bill having a bill wall including laterally opposite lips extending in longitudinal and altitudinal directions adjacent the outlet and having a prescribed altitudinal extent, the bill wall including a transition portion extending longitudinally between the inlet and the lips, and the lips being biased in lateral directions into engagement with one another along a slit extending altitudinally across the bill adjacent the bill end such that the outlet normally is closed against backflow of the fluid into the passage through the outlet by engagement of the lips along the slit; and at least one fold in the bill wall, the fold extending longitudinally along a corresponding lip and, when in a folded configuration, including overlying legs extending across the bill in an essentially altitudinal direction, essentially parallel to the slit, so as to overlie the corresponding lip, the fold having a prescribed altitudinal extent and a prescribed longitudinal extent such that upon fluid entering the passage at the inlet and exerting fluid forces upon the valve wall at the bill to unfold the at least one fold and move the legs of the fold laterally, the relative dimensions of the altitudinal extent of the legs of the fold and the altitudinal extent of the bill enables unfolding of the at least one fold and lateral movement of the legs of the fold to part the lips in lateral directions and open the outlet to permit the flow of fluid from the inlet for discharge through an opening at the outlet of the valve member in response to minimum fluid forces upon the bill, and for providing the opening with an increased maximum available perimeter.