A fluid delivery system which 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 valve housing having a first port associated with the pressurizing device, a second port associated with the low pressure fluid delivery system, an outlet port associated with a patient, and a pressure isolation port for connection with a pressure transducer. A first valve in a normally open position permits fluid communication between the first port and the second port and is movable to a closed position when fluid pressure in the first port increases to a predetermined pressure level. The first valve isolates the pressure isolation port from the first port when in the closed position. A second valve is associated with the second port and regulates fluid flow through the second port.