Abstract: A foam pump system for injecting chemical foamant into a firefighting stream includes a water pump, a foam pump, and an optional air compressor which are all connected to a common transmission. The transmission includes an input shaft which may be connected to a single power source (such as an engine of a fire truck) for driving the water pump, foam pump, and air compressor. The water pump, foam pump, and air compressor are preferably mounted (directly or indirectly) on the transmission to provide a compact unit that may be sold in modular form for ready incorporation into a firefighting apparatus such as a fire truck. The system also advantageously includes a hydrostatic transmission for selectively and accurately driving and controlling the speed of the foam pump and the resultant proportion of chemical foamant that is injected into the fire fighting stream.