Series 50 – Section 2.36 Venting and Leak Checking Procedures for a Natural Gas Engine (High Pressure System)

Section 2.36
Venting and Leak Checking Procedures for a Natural Gas Engine (High Pressure System)

To vent and leak check an operable engine, refer to "2.36.1 Venting an Operable Engine to Relieve Natural Gas Pressure" :‪

Section 2.36.1
Venting an Operable Engine to Relieve Natural Gas Pressure

Vent an operable engine as follows:‪

EXPLOSION ‪
To avoid injury from the explosion of natural gas, the engine must be kept in a well ventilated area away from open flames, sparks, and electrical resistance (heating) coils.‪

1. Shut off manual valves on natural gas supply tanks and main shutoff valve on natural gas fuel supply line.
2. Start engine and run until it stalls due to fuel starvation.
3. Check to make sure gage pressure at point on the natural gas fuel line to be vented has been reduced to zero. If not, repeat step 1. Then repeat step 2.
4. Disconnect the vehicle batteries using switch(s) in the battery compartment or by disconnecting battery ground cable.
5. Slightly loosen the CNG fuel line fitting to be serviced in a well-ventilated area to allow any remaining gas to vent.
6. Completely open the fitting that was slightly opened and allow to vent in a well-ventilated area.

Section 2.36.2
Venting an Inoperable Engine to Relieve Natural Gas Pressure

If the engine cannot run , use the following venting procedure to relieve the natural gas pressure downstream of the shutoff valve:‪

EXPLOSION ‪
To avoid injury from the explosion of natural gas, the engine must be kept in a well ventilated area away from open flames, sparks, and electrical resistance (heating) coils.‪

1. Shut off manual valves on natural gas supply tanks and main shutoff valve on natural gas fuel supply line.
2. Disconnect the vehicle batteries using switch(s) in the battery compartment or by disconnecting the battery ground cable.
3. Open a fitting to assure all pressure has been relieved in the natural gas vehicle fuel line.
4. Check all connections that were loosened for leaks after installation, service and troubleshooting are complete.

Section 2.36.3
Leak Checking the Natural Gas Fuel System

Use the following steps to check for leaks:‪

EXPLOSION ‪

To avoid injury from an explosion of natural gas, the following precautions must be taken:‪ Use a combustible-gas detector. Liquefied natural gas (LNG) is odorless and cannot be detected by smell. Compressed Natural gas (CNG) may be odorless and may not be detected by smell. Equipment fuel systems are the responsibility of the Original Equipment Manufacturer (OEM). Equipment fuel system guidelines must be closely adhered to when installing or servicing equipment. Refer to OEM guidelines specifying which maintenance procedures require venting of fuel lines and fuel tanks. LNG systems are pressurized and contain extremely cold (-162° C [-260° F]) fluids. Contact the fuel supplier or OEM for LNG safety requirements. Contact with LNG may cause personal injury (freezing). Vent systems on the equipment should be ducted to a safe area whenever equipment is in an enclosed area.

1. Spray soapy water or commercially available leak checking solutions on connections which are pressurized to working pressure. Bubbles will form if there is a leak.
2. Repair any leak by:
   1. Tightening connection using the fitting manufacturer's technique.

   Note: Bleed the fuel lines before replacing leaking components using the procedure in this section. This will prevent a discharge of gas.

   2. Replacing leaking component.
   3. Replace the pipe threaded connector with a new one if the leak is a pipe thread connection. Use anaerobic sealant with Teflon (such as SWAK®) applied to the threads.

      SWAK® is a registered trademark of the Cajon Company.‪

3. Re-check connection with procedure in step 1 .
4. Use a combustible gas detector to check for presence of natural gas. If natural gas is detected, continue looking for leaks until the locations of all the leaks are determined.
5. Repair the leak using the procedure in step 2 .