ClipArt ETC
"A valve in pumps with a single flap, hinged at one edge, and consisting of a plate of leather a little larger than the valve aperture. The valve box is generally one and a half times the diameter of the valve opening." — Williams, 1889

Clack-valve

"A valve in pumps with a single flap, hinged at one edge, and consisting of a plate of leather a little…