The present application relates to a breast pump. The breast pump has a chamber (12) and a membrane (22). The membrane (22) is receivable in the chamber (12) to separate the chamber (12) into first and second spaces (23, 24). The membrane (22) is also deformable in the chamber in response to a reduction of pressure in the first space (23) to cause a reduction of pressure in the second space (24). A limiter (16) is in the chamber (12) against which the membrane (22) is locatable to limit deformation of the membrane (22).