Abstract: An ejector pump having a plurality of longitudinally aligned chambers, each chamber including a pair of opposed end walls, at least two of the end walls having a nozzle and a one-way valve, with a connection to compressed gas to the most upstream of the nozzles, the pump having a single cylindrical pump body defining a cylinder or axially aligned cylinders with multiple end walls inserted therein, each wall having substantially the shape of a cross section through the cylinder or the respective cylinders. The end walls being secured to the cylinder at a point along the length of the cylinder or each end wall attached to the corresponding aligned cylinder.