A pump operated with compressed gas is disclosed herein. The pump has two separate cylinders which share a common wall. Pistons are attached to a common shaft that runs through the common wall. The pistons are disposed within each of the cylinders. The pistons divide the cylinders into gas and liquid chambers. The liquid chambers of the cylinder form a liquid system and are in fluid communication with the liquid inlet and outlet. The gas chambers of the cylinders form a gas system and are in communication with gas inlet and outlet. A manifold switching mechanism controls routing of compressed gas to either one of the gas chambers to operate the gas operated pump by way of a spool valve or a shuttle valve mechanism. The pump may also have an automatic shutoff valve which shuts off operation of the pump when liquid from a liquid source has been depleted.