An osmotic delivery system for controlled delivery of a beneficial agent includes an implant capsule having a beneficial agent reservoir, an osmotic agent which expands on contact with fluid imbibed through a permeable membrane retained by the implant capsule, a delivery port, and a valve for opening and closing the delivery port. When the osmotic agent expands, a pressure is exerted against a separating member positioned between the beneficial agent reservoir and the osmotic agent. The separating member moves within the capsule, thereby forcing the valve to move a distance such that the beneficial agent can exit the reservoir through the delivery port.