A breast pump system comprises at least one wearable milk collection hub connected via an air line to a combined external air pump and control unit. Each milk collection hub comprises: (a) a breast shield made up of a breast flange and a nipple tunnel; (b) a flexible diaphragm that is configured to prevent milk from reaching the external air pump; (c) an outer shell that is configured to removably attach to the breast shield, such that, when attached, the breast shield and outer shell form a vessel for collecting milk; and (d) a diaphragm cap that is configured to be secured over the diaphragm, forms part of the front face of the outer shell, and includes a port connected to the air line.