Abstract: Duck-bill type check valves each include an inlet, an outlet spaced longitudinally from the inlet, and a bill adjacent the outlet and having at least one fold extending longitudinally along the bill for enabling unfolding of the at least one fold to open the outlet and permit the flow of fluid from the inlet for discharge through an opening at the outlet in response to minimum fluid forces upon the bill, and to provide the opening with an increased maximum available perimeter.

Abstract: A pinch valve has a resiliently flexible tubular valve member folded upon itself at an intermediate portion of the length of the valve member to establish a folded configuration including a longitudinally extending folded portion, preferably in the form of folds, and an operator for selectively exerting a lateral force upon the valve member to unfold the folded portion, or folds, so as to restrict the flow of fluid through the valve member by closing down the valve member. Upon release of the lateral force, biasing forces established by memory characteristics in the construction of the valve member return the valve member to the folded configuration to open the valve member for unrestricted flow of the fluid.