Issued June 2020
Compressed Natural Gas (CNG) Option
Copyright 2020, Heil Environmental
Printed in U.S.A.
210
CNG FUEL SYSTEM COMPONENTS
The following pages detail a typical CNG system
configuration. Your CNG fuel system configuration may
vary.
A.Fuel Management Module (FMM) Functions
The CNG Fuel Management Module serves multiple
functions within a natural gas vehicle (NGV) fuel system.
These functions include:
Storage tank refueling
Transfer fueling (defueling)
Pressure display of high pressure side of system
Pressure display of low pressure side of system
Manual and ignition controlled fuel shut-off
Pressure reduction from storage tanks to engine
supply
Fuel system filtration
Liquid removal from fuel system
B.Fuel Management Module (FMM) Components
1. Manual Shut-Off Valve
The FMM Manual Shut-Off Valve isolates the fuel
storage system from the engine.The manual shut-off
valve handle is RED and is located on the left front of
the fuel control module. Rotate the handle clockwise
so arrow points right to the ‘OFF’ position to prohibit
fuel flow from the tanks to the vehicle’s engine.
Rotate the handle counterclockwise so arrow points
up to the ‘ON’ position to allow fuel flow from the
tanks to the vehicle’s engine.
2. High Pressure Gauge
The high pressure gauge indicates the fuel pressure
in the fuel system. The gauge has a range of 0 to
5000 psi. When cylinder(s) are full and the cylinder
Manual Shut-Off Valve is open, the pressure reading
should read approximately 3600 psi.
3. Low Pressure Gauge
The low pressure gauge indicates the fuel pressure
sent to the engine.
Momentum FMM (CNrG Tailgate): The gauge has a
range 0 to 150 psi. Normal engine operating
pressure is 70-100 psi for these Cummins CNG
engines:
8.9 L ISL G (2007+)
11.9 L ISX12 G (2013-2018)
8.9 L L9N (2018+)
11.9 L ISX 12N (2019+)
Agility FMM (Top of Body and Back of Cab): The
gauge has a range 0 to 150 psi. Normal engine
operating pressure is 60-100 psi for Cummins
Westport ISX 12N engines and 70-140 psi for all
other engines.
4. Fill Receptacles
Fill receptacles are used to fill the CNG storage
cylinders with fuel. There are two sizes: standard
NGV1 (slow) or HD bus transit (fast) fill. The
receptacles are equipped with built-in check valves to
prevent fuel from escaping when the fuel fill nozzle is
connected and disconnected.
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