The membrane rests on this continuous and raised rim 41124 providing for a seal between the half of the pod pumps, 4820, 4828 and balancing pods 4812, 4822 in the bottom plate 41100 and the half of the pod pumps 4820, 4828 and balancing pods 4812, 4822 in the top plate (not shown, see FIGS. 410A-410D). 7.1 Membranes In the exemplary embodiment, the membrane is a double o-ring membrane as shown in