Fuel Tank Pressure Release Valve: Description and Operation

FUEL TANK PRESSURE RELIEF DEVICE (PRD)

The CNG fuel tank is equipped with a thermally activated PRD valve. The PRD is necessary in order to protect the CNG fuel tank from excessive pressure build-up in the event the tank is exposed to high temperatures. The PRD is sealed internally with a thermally sensitive metal valve. When the PRD is exposed to temperatures near 102°C (215°F), the metal valve will melt and allow the CNG fuel tank pressure to fully vent to the atmosphere. The PRD will not close once activated. The Type 4 fuel tank PRD is externally threaded into an open port of the high pressure lock-off (HPL) solenoid valve. The PRD port is not controlled by the HPL solenoid valve and is directly open to the internal tank pressure. The CNG fuel tank must be completely vented prior to removing the external PRD. The external PRD should be inspected regularly. Refer to Fuel Tank Inspection (Type 4 Tank).