This is allowable as long as the pressure in the cylinder does not exceed 4,500 psi during the fueling process, nor afterward, and the “settled” pressure at 70° F does not exceed 3,600 psi. Anytime the temperature of the gas in a cylinder is higher than 70° F, the full cylinder pressure will be greater than the commonly rated 3,600 psi service pressure at 70° F. There have also been other serious incidents in which the container PRD was not activated by the excess pressure and the container ruptured.Īccurate temperature compensation allows dispensers to place a full fuel load on the vehicle during all weather conditions. The released fuel was ignited and the garage and vehicles burned. The result was the pressure in the container increased to over 5,000 psi, causing a pressure relief device (PRD) to quickly vent the entire fuel load. In the morning, the vehicle was then moved to a heated service garage where temperatures were much warmer. A vehicle was time-filled outdoors on an unusually cold winter night and without accurate temperature compensation the approximate station pressure setting was 3,600 psi. The following recent serious incident illustrates this point. This is because the temperature of the gas in the container may increase after fueling if the temperature of the environment increases before fuel from the container is used and pressure is reduced, which may occur with warming outdoor temperatures or when parking indoors. However, limiting the maximum pressure in the cylinder is not as simple as limiting the pressure dispensed to the vehicle. The underlying safety rationale for limiting the maximum pressure in CNG containers and equipment may seem obvious. Rationale/Supporting Arguments for Recommendations Why Compensate for Temperature? If the dispensers do not comply, the operator should seriously consider upgrading the equipment to provide the enhanced level of safety provided by these requirements when filling vehicles.
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