A double diaphragm pump including an air manifold, two air chambers to either side of the air manifold, two pump chambers to either side of the air chambers and diaphragms extending between the air chambers and pump chambers are stacked together in horizontal assembly. Intake and discharge manifolds span this distance to intake and exhaust ports associated with the pump chambers. One-way valves having valve bodies with passages therethrough are arranged between the manifolds and the pump chambers. The valve bodies have inlet mounting surfaces and outlet mounting surfaces with circular attachment flanges radially extending from these mounting surfaces. The circular attachment flanges each define a central axis which on each valve body are parallel and laterally displaced from one another. Concavities extend inwardly from the valve bodies from the inlet and outlet mounting surfaces. The angle between the central axis in the direction of the adjacent mounting surface and the surface of either concavity is acute and does not exceed approximately 60.degree..