4.7. Maintaining HP Fuel Filter (Manifilter)

Figure 27. Bleed valve location within the FMM.

Regular Manifilter high-pressure (HP) fuel filter
element replacement is vital for maintaining CNG
fuel system performance. Always replace the
element at or before the recommended intervals.

Bleed valve (2), Manifilter (1).

Table 7a. Manifilter HP fuel filter element replacement intervals.*

1

The system is now fully depressurized up to the
supply solenoid valve.

Duty
Cycle
Normal
Severe

Miles /
Kilometers

30000 / 48000
15000 / 24000

*Whichever comes first.

When loosening fittings for the first time, a small
amount of gas may leak out of any fitting
downstream of the supply solenoid valve; this is
normal.

Hours Months
1000
1000

9
9

Element replacement interval could be more
frequent depending on fuel station cleanliness and
fuel quality.

It is no longer necessary to drain the Manifilter for
regular maintenance.

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4.7.1. Draining the Manifilter Assembly
1. Depressurize fuel system. Refer to Section 4.5.
2. Slowly remove Manifilter drain plug (2) using an
11/16-in. wrench. Figure 28
1

5

DO NOT allow silicone lube to contaminate filter
bowl or element.

7. Reinstall Manifilter bowl (7). Figure 29
Tighten Manifilter bowl to 50±1 ft-lbs
(67.79±1.36 Nm).
Table 7b. Manifilter torque specifications.

3

Manifilter Torque Specifications

2

4

Figure 28. Manifilter assembly FMM location and drain plug.
Manifilter housing (1), drain plug (2), bowl (3),
solenoid valve (4), pressure regulator (5).

3. Drain Manifilter (1) until no liquid or residue
remains. Figure 28

Component
Filter bowl
Hex head plug
Flow port fittings
(IN/OUT)

ft-lbs
50±1
25-30

Nm
67.8±1.36
33.9-40.7

25-30

33.9-40.7

1

4

Collect any fluid and dispose of properly.

5

4. Inspect drain plug O-ring. Figure 29 Obtain a
replacement from Gillig if necessary.

6

5. Use an 11/16-in. wrench to replace Manifilter
drain plug (2). Figure 28

2

Torque Manifilter drain plug to 26 ft-lbs
(35 Nm).
4.7.2. Replacing the Manifilter Element
To replace the fuel filter element inside the
Manifilter:
1. Depressurize the system. Refer to Section 4.5.
2. Drain Manifilter. Refer to Section 4.7.1.
3. Unscrew Manifilter bowl (7) using a filter bowl
removal tool or a 1-1/4-in. wrench. Figure 29

3

7
Apply silicone
lube to
Manifilter bowl
threads

8
9

Figure 29. Manifilter components.
Manifilter housing (1), bowl O-ring (2), element O-ring (3),
element housing (4), HP filter element (5), housing base (6),
Manifilter bowl (7), drain plug O-ring (8), drain plug (9).

4. Remove and replace old filter element (5). Figure
29
5.

6.

Apply a thin coat of lubricant (supplied
with element replacement kit) to element
housing O-ring (3) and filter bowl O-ring
(2). Figure 29
Lubricate Manifilter bowl (7) threads with
silicone lubricant. Figure 29

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4.8. Maintaining Low-Pressure Fuel Filter
4.8.1. Low-Pressure Fuel Filter Replacement
and Service

Avoid cross threading.

The low-pressure (LP) fuel filter should be drained
daily and replaced every 12 months.
Depending on fuel quality and characteristics, filter
drainage and replacement may be required more
frequently than the prescribed schedule.

4.8.2. Draining LP Fuel Filter & Replacing the LP
Filter Housing
1. Depressurize the system. Refer to Section 4.5.
2. Once the work area has been depressurized, the
LP filter housing may be drained by turning the
drain cock counterclockwise or until liquid begins
to flow. When the flow stops, turn drain cock
clockwise until fully seated hand tight. Figure 30

Figure 30. LP fuel filter drain cock location.

3. To replace LP filter, remove LP filter housing by
turning it counterclockwise. This step may
require a strap wrench or grip pad. Dispose of
the filter housing per regulations. Figure 30
4. Install new LP filter. The filter gasket is lubricated
at the factory, no additional lubrication is
required. Figure 30
5.

Tighten new LP filter housing by hand until
gasket contact is achieved, then turn the filter
housing another 3/4-turn. Figure 30

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4.9. Supply Solenoid Valve (SSV)
The supply solenoid valve (SSV) is a two-way valve
activated electrically by the ignition switch. As its
name suggests, the SSV controls the flow of fuel
from the cylinders to the adjacent pressure
regulator. By default, the SSV is in the
“OFF/CLOSED” position with ignition OFF. Figure
31

Supply solenoid valve coils are designed to operate
continuously for a lifecycle of 22,000 hours. Coils
generate significant heat and require adequate
open space for dispersion. When a coil remains
energized for extended periods of time the
assembly will be hot. Although the coil is designed
to operate under these conditions smoke or the
scent of burning coil insulation may be an
indication of overheating; in which case the coil
may need to be replaced.

1
Figure 31. Supply solenoid valve (1) location in FMM.
Table 8. Supply solenoid valve (SSV) troubleshooting.

Problem

Possible Causes / Items to Check
Check electrical supply with a voltmeter. Voltage
must match nameplate rating.

Valve fails to operate.
Valve fails to operate.
Valve is sluggish or inoperative, but
there are no issues with power supply
and/or pressure

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1. Check the electrical supply with a voltmeter.
Voltage must match nameplate rating.
2. Check coil with an ohmmeter for an open or short
condition.
3. Verify pressure complies with nameplate rating.
4. If no apparent system problem exists, remove and
replace the solenoid valve.

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4.10. Cylinders

of the container and any repairs since the
container was last inspected.

CNG cylinders that have been involved in an
incident that registers at level 2 or 3 should be
depressurized prior to inspection.

Failure to perform regular or emergency
inspections may result serious injury or death.

4.10.2. Cylinder Venting Procedure
Before depressurizing a cylinder, ground the
venting orifice with a minimum 3-gauge wire to an
appropriate ground source at least 8-ft (2.44m)
underground. Rapid discharge can generate
enough static electricity to ignite escaping gas.

4.10.1. Inspecting Cylinders
The composite containers on the vehicle are
manufactured to comply with FMVSS 304, NAI/IAS,
or the CSA B51 Part 2 specifications.
Cylinders must be inspected by a qualified cylinder
inspector every 3 years or 36,000 miles (58000 km),
whichever comes first.

The inspector should provide a report for each
cylinder and place an inspection label on each of the
cylinders. Containers must also have permanent
labels in accordance with applicable regulations.
These labels provide valuable information to both
the inspector and the manufacturer.
Cylinders must be inspected immediately if:
1. The vehicle has been in an accident.
2. The fuel container or vehicle has been subjected
to fire, impact, excessive, heat, or any other
means that may have caused external or internal
damage.
3. Unusual behavior is observed. This may include
but is not limited to, emission of natural gas odor,
unexpected loss of gas pressure, snapping or
hissing sounds, rattling, and any other indications
of loose parts.
4. The fuel tank has been transferred to another
vehicle or the tank installation has been altered
significantly.
5. Question system owner/operator about incidents
or conditions which may have caused damage to
the fuel container. These include but are not
limited to the following: dropping the container,
impacts, exposure to excessive heat, fire or harsh
chemicals
and
vehicle
accidents.
The
owner/operator should keep records of any
unusual observations as well the service history
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When venting a cylinder always do so in an open
area with good air circulation and no sources of
open flame, ignition, or heat. Do not vent the system
where flammable gas is permitted to accumulate
and potentially ignite. Refer to Section 5, “Defueling
Preparation and Procedures.”

4.11. Valve Maintenance
Valves do not require regular maintenance.
If a malfunction should occur, check for leaks first
and replace valve if necessary.

4.12. Pressure Relief Devices (PRDs)
The pressure relief devices used on this system
have been designed in accordance with ANSI-CSA
PRD-1 and meet or exceed the requirements for fuel
container pressure relief devices onboard natural
gas vehicles. Figures 32 and 33
4.12.1. PRD Visual Inspection
PRDs must not have any aesthetic or structural
deficiencies. Remove any visible contaminants,
debris, and moisture from the outlet port of the PRD.
Figures 32 and 33
PRDs do not have consumable parts and require no
additional maintenance other than visual inspection.
PRDs that do not pass visual inspection must be
replaced. Figures 32 and 33
4.12.2. PRD Vent Line Visual Inspection
PRD vent lines have a drainage hole in the lowest
point on the tube. All PRD vent lines should be
checked for blockage during component inspections
to prevent water build-up that can corrode the
components.

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If any PRD vent caps are missing, the vent tube
should be inspected immediately and new caps
installed. PRD vent tubes are not under pressure
making it safe to service the cap.

The COMPRESSED FUEL line is the tubing that is
CLOSEST to the handle on the valve. If uncertain,
trace the line in question. If a line connects to a 3/4in. fuel supply line, it is a high-pressure fuel line and
should not be handled unless the system is
depressurized. If a line is open on one end with a
cap it is a PRD vent line and is not under pressure.

Verify lines to be loosened or removed are vent
lines and NOT fuel or PRD supply lines. Loosening
or removing a fuel line can result in serious injury
because it contains high-pressure gas.

1

2

Figure 32. Eight cylinder system cylinder plug end with PRD vent lines (1) and PRD vent tube cap (2).

Electric solenoid cylinder valve
4

2
1

4
3

3
2

1

Manual cylinder valve
Figure 33. Eight cylinder system cylinder valve end.
Valve manual knob (1), high-pressure fuel tubes (2), PRD lines (3), PRD vent tube caps (4).

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4.13. Fill and Defuel Receptacles
Installations shall be conducted in accordance with
regulations stipulated by the authorities having
jurisdiction (AHJ).

4.13.1. Receptacle Maintenance
Receptacle external surfaces must be kept clear of
contaminants and debris. Dust caps (4) and (5) are
provided to prevent debris intrusion and extend
system life. Figure 34

1

Receptacles connect to the FMM via straight
threads to female SAE ports.

4.13.2. Transit (Fast) Fill Freeze-Up

3

Transit (fast) fill receptacles are prone to freezing
during rapid filling procedures due to “wet”
compressed natural gas conditions.

To remedy freeze-up, return FMM 1/4-turn manual
shutoff valve (2) to the “OFF/CLOSED” position until
external icing is no longer visible and the internal
poppet assembly achieves a seal. Figure 34

2
4

5

Figure 34. FMM receptacles.
Transit (fast) fill receptacle (1), 1/4-turn manual shutoff valve (2),
defuel receptacle (3), fast fill receptacle dust cap (4) defuel
receptacle dust cap (5). NOTE: Smart Gauge equipped FMM face
plate shown; non-Smart Gauge face plate is similar.

External mounting hardware, receptacle O-rings
(not visible), and receptacle dust caps should be
checked periodically to ensure components are
functioning properly without leaks. Figure 34

Once sealed, the check valve will resume normal
functionality and gas will cease to escape from the
receptacle.
The receptacle is to be used solely on a CNG
vehicle. The receptacle is designed to receive with
AGA/CGA NGV1 certified fueling nozzles. For
information
on
coupling
and
uncoupling
procedures, please
consult detailed OEM
instructions provided with CNG fueling dispensers.

If component functionality is compromised or a leak
is detected, consult a qualified technician. Only
trained accredited personnel should service,
maintain, remove, or install a fueling receptacle.

The vehicle operator must not tamper, alter,
disconnect, or dissemble any receptacle or
component connected to a receptacle.

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5. Defueling Preparation and Procedures
A CNG vehicle may need to be defueled for maintenance or storage. The best and safest way to defuel a CNG
system is to transfer fuel back to a dispensing station, if so equipped.
Always follow CNG dispensing station specific procedures.

The basic defueling procedure is provided for use with CNG cylinders equipped with manual cylinder
valves or with electric solenoid cylinder valves. However, CNG cylinders equipped with electric
solenoid cylinder valves have additional considerations for complete system defueling; please refer to
bulletin ENP-729, “Type 4 CNG Cylinder Defueling with Electric In-Tank Solenoid Valves.”
5.2.1. Vent to Atmosphere
First, verify whether this method is legal. Local air
quality regulations may restrict the release of
methane into the atmosphere

Use a slow flow when transferring fuel to
reduce static electricity/electrostatic
discharge and to avoid freezing.

5.1. Basic Rules for Defueling
1. Only CNG qualified personnel should attempt
these processes.
2. Consume as much fuel as possible prior to
defueling.

If atmospheric venting is acceptable, a venting
facility compliant to regulations must be used.
Figure 35

5.2.2. Compressor Transfer

3. Secure an approved place to put the fuel
removed from the vehicle.

In this defueling method, a compressor at the fueling
station extracts fuel from the vehicle.

4. Notify nearby personnel prior to defueling.

5.2.3. Return to Supply

5. Always ground the vehicle and the fuel
system.

The third defueling method returns fuel to a
distribution system.

6. Never defuel indoors.
7. Always wear appropriate PPE.

When using this process, pressure in the vehicle
tank and the supply system pressure will equalize
leaving pressure in the vehicle fuel system.

8. Be familiar with evacuation routes.

5.2. Defueling Requirements
CNG must be removed from the vehicle at an
approved facility.

5.3. A Typical Venting Facility

There are three common defueling options: vent to
atmosphere, compressor transfer, and return to
supply.

The following information is provided in the absence
of formalized procedures from local authorities and
governing bodies. Figure 35 represents a typical
venting facility.

In all cases, both the vehicle and the fueling system
must be grounded to prevent static electricity buildup.

Venting CNG to atmosphere to requires care.
Improper equipment or procedures raise the risk of