Abstract: A double diaphragm pump driven by alternating charges of air includes air chambers and pump chambers to form pump cavities. Diaphragms extend across the pump cavities and are held by their periphery between the mating pump chambers and air chambers. Elbows are coupled with the pump chambers at the inlets and outlets thereof with each of the elbows being identical and including a valve cavity to receive a ball valve. Each ball valve includes a seat with a threaded portion accommodated in either the elbow when the elbow is used at the inlet or the pump chamber at the outlet. The ball valves further include a ball and a ball cage. The components are sized to insure that when the ball is fully unseated, the minimum cross-sectional flow area is at the pump outlet. Sealing surfaces are associated with the valve seat and the associated structure to receive a compressible seal. Annular bolting flanges allow components to be reoriented for particular applications.