A portable surface cleaning apparatus including a liquid dispensing system including a flexible bladder defining a fluid supply chamber for holding a supply of cleaning fluid and a fluid recovery tank having a fluid recovery chamber for holding recovered fluid and housing the flexible bladder. A fluid passageway between the fluid supply chamber and the recovery chamber equalizes the pressure in the flexible bladder as the cleaning fluid is dispensed from the supply chamber and the dirty liquid is collected in the recovery chamber. A lid mounted on the tank defines an expansion chamber having an inlet opening, an outlet passage, and first and second diverters against which the working air flow reverses direction twice between the inlet opening of the expansion chamber and the tank. The working air conduit includes a manual actuator knob having an over-center linkage mechanism connected to a conversion valve for movement between first and second positions and thereby selectively moving the conversion valve between open and closed positions, whereby fluid communication between the tank and the suction nozzle is selectively opened and closed. A flow indicator is mounted to the base module and has a visibility window observable to a user and the flow indicator is disposed in the fluid supply conduit and is responsive to the flow of fluid through the fluid supply conduit to visually indicate the flow of fluid through the supply conduit to the user. A pump primer is connected to the pump and has a housing defining a priming chamber with a valved opening connected to the vacuum source, an inlet opening is connected to the fluid supply chamber, and an outlet opening is connected to an inlet for the pump. A motor drives the impeller, the pump and an agitation brush. An elevator assembly is reciprocally mounted to the base module and movable in response to movement of the upright handle from an operative position to the upright position for raising an agitation brush.