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1. A breast pump assembly comprising:
a housing assembly including a piston housing and a drive housing having an opening in direct communication with atmospheric pressure; a piston assembly including a vent piston and a drive piston, the vent piston having a top wall and a channel defined by the top wall, a side wall and a center post where a vent is defined to extend through the side wall in communication with the channel, the drive piston having a top wall with a vent passage defined therethrough; a rolling diaphragm including an outer end, an outer margin disposed adjacent the outer end, where both of the outer end and outer margin are sealingly captured between the piston housing and the drive housing, an inner end, and an inner margin disposed adjacent the inner end, where the inner margin is sealingly captured between the vent piston and the drive piston to cooperatively define a pressure chamber between the diaphragm, piston housing and vent piston; and a permanently unobstructed continuous passageway across the diaphragm that is disposed at atmospheric pressure defined by the vent in direct communication with the channel, the channel in direct communication with a portion of the inner end that is spaced from the center post, and the vent passage in direct communication with the inner end portion and the opening, wherein the diaphragm is movable between a vacuum orientation and a vent orientation in response to cyclic movement of the piston assembly, such that the vacuum orientation is defined when an outer opening of the vent is sealed by the diaphragm, and the vent orientation is defined when the outer opening of the vent is uncovered by the diaphragm so that the pressure chamber is in direct communication with atmospheric pressure via the permanently unobstructed continuous passageway across the diaphragm, and wherein the diaphragm is disposed in the vent orientation between 15% and 60% of each cycle of the piston assembly. |
