day is equal to the same amount of gas at a higher
pressure on a warm day. The fuel station dispenser
has a temperature-pressure compensating device,
which accounts for ambient temperature during
fueling. See
Table 19.1 for approximate full cylinder
pressures at various temperatures.
CNG Temperature/Pressure Compensation Values
Temperature:
°F (°C)
Fill Station Pressure Set Point
3000 psi (20 684
kPa) Set Point
3600 psi (24 821
kPa) Set Point
100 (37.8) 3415 (23 546) 4086 (28 172)
90 (32.2) 3276 (22 587) 3909 (26 952)
80 (26.7) 3138 (21 636) 3754 (25 883)
70 (21.1) 3000 (20 684) 3600 (24 821)
60 (15.6) 2861 (19 726) 3445 (23 752)
50 (10) 2723 (18 774) 3288 (22 670)
40 (4.4) 2584 (17 816) 3131 (21 587)
30 (-1.1) 2446 (16 865) 2973 (20 498)
20 (-6.7) 2307 (15 906) 2814 (19 402)
10 (-12.2) 2169 (14 955) 2655 (18 306)
0 (-17.8) 2031 (14 003) 2495 (17 202)
-10 (-23.3) 1893 (13 052) 2336 (16 106)
-20 (-28.9) 1755 (12 100) 2180 (15 031)
-30 (34.4) 1616 (11 142) 2024 (13 955)
-40 (-40) 1477 (10 184) 1868 (12 879)
Table 19.1, CNG Temperature/Pressure Compensation
Values
Use the following steps to fuel a CNG vehicle.
1.
Shut down the engine and apply the parking
brake.
IMPORTANT: Close all windows and doors
during the fueling process. Keeping windows
and doors closed allows for easier leak
detection inside the cab after fueling.
WARNING
Natural gas fuel tanks, lines, and valves are
always pressurized. Always observe safety
precautions. Failure to do so could lead to loss
of control over a filling hose or to ignition of the
natural gas, which could cause serious bodily
injury, death, or severe property damage.
2.
Ensure all fuel cylinder shutoff valves are open.
See
Fig. 19.2.
3.
Ensure the vehicle fuel system main shutoff
valve is open.
4.
Open the CNG fuel panel access door and
remove the dust cap from the vehicle fuel fill
port.
5.
Ensure the O-ring is present inside the fuel fill
port. If the O-ring has been dislodged or is
missing, the station dispensing nozzle will not
connect securely to the fill port.
6.
Turn the selector knob on the service pump to
the VENT position, if equipped.
7.
Connect the quick coupling on the dispensing
nozzle securely to the vehicle fuel fill port.
8.
Turn the selector knob on the service pump to
the FILL position, if equipped.
IMPORTANT: If at any time the service pump or
vehicle begins to vent CNG uncontrollably, notify
04/22/2010 f470554
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2
3
4
5
7
8
6
1. Fuel Cylinder Storage Box
2. Fuel Cylinder Shutoff Valves (qty 5)
3. High-Pressure Gauge
4. Low-Pressure Gauge
5. Fuel Fill Port
6. Dust Cap
7. Manual Shutoff Valve
8. Fuel Panel Access Door
Fig. 19.2, CNG Fuel Cylinder Storage Box (5-cylinder
system shown)
Natural Gas Vehicle Information
19.3
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