A diaphragm is a sheet of a semi-flexible material anchored at its periphery and most often round in shape. It serves either as a barrier between two chambers, moving slightly up into one chamber or down into the other depending on differences in pressure. A retainer is a mechanism that positions, as a device, frame, or groove that restrains, holds in place, or guides. A retainer may be also be a clip, bracket, or similar component that prevents a part within a machine from moving.