This device from CHART has a rubber piece that tightens to the neck of the dewar. By screwing it on tightly, it creates pressure to dispense the liquid nitrogen. This device is affixed to your dewar at all times and is only removed during filling of the dewar. It creates 3-5 psi of usable pressure. It has pop off and pressure release valves for safety. If ordering for a personal dewar, please indicate the size of the tank and model number so we can fit your neck rubber accordingly.