The fluid delivery system includes a pressurizing device for delivering injection fluid under pressure, a low pressure fluid delivery system, and a pressure isolation mechanism. The pressure isolation mechanism includes a first lumen associated with the pressurizing device, a second lumen associated with the low pressure fluid delivery system, and a pressure isolation port. The first valve is in a normally open position permitting fluid communication between the first lumen and the second lumen and movable to a closed position when fluid pressure in the first lumen reaches a predetermined pressure level. The first valve isolates the pressure isolation port from the first lumen in the closed position. A second valve is associated with the second lumen and regulates fluid flow through the second lumen. The second valve may be a disk valve defining one or more passageways in the form of slits through the body of the disk valve.