Abstract: An implantable single or dual-lumen or more lumen device for repeated accessing vessels within a body. The device uses a resilient material to form a seal, and has a smooth streamlined flowpath with no flow discontinuity. The device is joined to a catheter, in most cases, such that fluids can be extracted from or injected into the vessel to be accessed. The device is designed for the high flowrates, on the order of 150 and greater milliliters per minute, associated with hemodialysis, plasmapheresis, and other fluid exchange therapies. In such applications smooth flow streaming is important to minimize damage to the blood. A corresponding straight-needle apparatus is designed to mate and lock with the access device, where alignment and open flowpath is ensured. A valve seal incorporates opposing very hard surfaced guide elements that are retained and in intimate contact with the seal itself.