Beyond Zero Tips: CNG Tank Fueling Tips

By Greg Roche

All public access stations generally have a standard CT1000 CNG dispensing nozzle. These nozzles are typically yellow. Some stations have high flow CT5000 nozzles intended for fueling trucks and busses, which are typically black. The CT5000 nozzles fill faster than CT1000. CT1000 and CT5000 nozzles operate the same although CT5000 nozzles are larger and bulkier to handle.

  • CT1000 Nozzle        CT5000 Nozzle

CNG trucks have a fuel gauge in the cab and a pressure gauge on the CNG tanks. The fuel gauge in the cab is approximate. The pressure gauge on the tanks is the most accurate measure of the amount of fuel in the tank.

Station pumps automatically turn off when the tanks are full. The pressure at filling completion will be in the range of 3600 to 3900 PSI. The fuel warms during the dispensing process and the pressure will naturally decrease as the fuel cools down to ambient temperature. This is normal.

The station dispenser has a pressure gauge on the pump. The pump pressure gauge and the truck pressure gauge readings will match.

According to Agility, one manufacturer of CNG systems, fueling should be considered as follows noting of course that there is a difference between running under the strain of going up the Grapevine with a heavy load versus bobtailing around the port:
500 PSI – Start fueling
250 PSI – Danger – truck is very low, get fuel now
150 PSI – Truck may not run due to insufficient fuel pressure
It could be helpful to mark 500 PSI and 3600 PSI on the gauge.

Truck tank gauge (below left) shows 2200 PSI (61% full) before filling. Station gauge (below right) matches truck tank gauge, indicating the gauges work.

Truck tank gauge (below left) is at 4,000 after filling. Pressure after filling is greater than 3600 because gas warms up during dispensing. The pressure will drop after the gas cools down. Station gauge (below right) matches tank gauge, indicating the gauges work.

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