Testing the LNG Vacuum Integrity
- Ensure the fuel tank is between 50 and 75 percent full.
- Check the fuel tank pressure gauge ( see Fig., Item 8) to ensure that pressure is within the normal range
of 120 to 150 psi (827 to 1034 kPa).
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Pressure Control Regulator
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Vapor Shutoff Valve
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Fuel Fill Hose
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Secondary Relief Valve (red cap)
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Fuel Fill Fitting
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Fuel Level Sender Box
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Primary Relief Valve
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Tank Pressure Gauge
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Fill Vent Fitting
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Excess Flow Valve
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Fuel Shutoff Valve (liquid)
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Fill Check Valve
Fig. 1, LNG Tank Plumbing Components
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- Inspect the fuel tank for signs of frost spots or outer surface sweating. Frosting or condensation on the outer surface of the fuel tank may indicate a loss of vacuum.
- Check for a large variance in temperatures between the fuel tank and the fuel tank shroud. A large variance in temperatures between the fuel tank and the shroud may indicate a loss of vacuum.
- Operate the vehicle for ten minutes. Shut down the engine, apply the parking brakes, and note the time.
- Wait fifteen minutes after shutting down the engine, then record the fuel tank pressure and note the time.
- Allow the vehicle to stand for at least eight hours, then record the fuel tank pressure again.
- Use Table to
determine whether the pressure increase is within an acceptable range.
Table 1, Vacuum Integrity Test Results
Pressure Increase Over Eight-Hour Period
Remedy
Less than 20 psi (138 kPa)
None – Tank is normal
20 to 50 psi (138 to 345 kPa)
Monitor tank and test vacuum integrity again at next maintenance date
More than 50 psi (345 kPa)
Remove vehicle from service and evacuate the tank per the tank manufacturer's instructions
Table 1, Vacuum Integrity Test Results