An exemplary refill unit for a foam dispenser includes a container for holding a foamable liquid and a liquid pump connected to the container and an outlet nozzle. The liquid pump has a rigid back plate and a flexible membrane. The flexible membrane and the rigid back plate form an arcuate shaped liquid pump chamber. The rigid back plate has a liquid inlet located proximate a first end of the arcuate shaped pump chamber and a liquid outlet located proximate a second end of the arcuate shaped pump chamber. The liquid pump is actuated by progressive compression of the flexible membrane against the back plate.