A foam pump including a housing and a piston that reciprocates within the housing is disclosed herein. The piston has a hollow portion and an orifice through the wall of the piston. A first seal located proximate the upper end of the piston provides a seal between the piston and the housing. A liquid inlet is located in the side wall of the housing at a point lower than the top of the piston. A one-way liquid inlet valve is located proximate the liquid inlet and a one-way liquid outlet valve is located prior to the liquid outlet. A charge chamber is defined at least in part by the liquid inlet valve, the liquid outlet valve, a wall of the piston and a wall of the housing.