Foam dispensers, refill units for foam dispensers, and liquid pumps for use in foam dispensers are disclosed herein. In one embodiment, an inverted foam pump includes a compression chamber having an inlet valve and an outlet valve. The compression chamber is in fluid communication with a flow restrictor, an atomizer, a mixing chamber, a foaming chip and an outlet. The inlet valve, outlet valve, flow restrictor, atomizer, mixing chamber, foaming chip and outlet extend along a common axis. An air inlet is included that extends into the mixing chamber; the air inlet is an opening to atmospheric pressure. During operation, the liquid pump is located below the liquid container and liquid flowing from the compression chamber is accelerated and atomized. The atomized liquid enters the mixing chamber at a velocity sufficient to draw in air from the air inlet to mix with the liquid to form a foam.