An expansible chamber pneumatic system, for example a fluid pump system, includes two or more double-acting diaphragm pumps, each with symmetrical left and right pump housings, each housing including an air chamber and a fluid chamber separated by a movable diaphragm. The diaphragms are connected for reciprocating movement in unison to pump fluid through their respective fluid chambers. Each pump includes an air valve actuated by Control air to direct Process air into one of the air chambers, simultaneously releasing used Process air from the other air chamber to thereby move the diaphragms, thereby to pump fluid. A pilot valve directs Control air to the air valve to position the air valve. The pilot valve is responsive to diaphragms reaching their travel limit in one direction to direct Control air to reverse the directions of Process air flow through the air valve to thereby reverse the movement of the pump diaphragms. Control air exhausts through the pilot valve to atmosphere. Process air exhausts through the air valve from one pump to become input or motive air for the next pump.