Support
structure
or building
wall

FMM
Defuel nozzle lever

Ground cable – vehicle end
(earths fuel system at FMM when
defuel nozzle is connected)

Earth grounding
rod/connection

Ground cable – stack end
(earths vent stack)

Figure 35. Required defueling connections and typical atmospheric venting facility equipment diagram.

5.3.1. Venting Facility Minimum Equipment Figure
35


Vent pipe consisting of a 2-in. (51 mm) diameter
steel pipe attached to a support structure. The
pipe must extend a minimum of 2-ft. (0.6 m)
higher than the support structure and a least 10
ft. (3 m) above ground level. The vent pipe must
be connected to an electrical ground extending
at least 8-ft. (2.44 m) underground.

Additional Recommended Equipment


Portable fire extinguisher in an easily
accessible location at the defueling facility. The
extinguisher should have a rating no less than
20-B:C.



Large signage indicating “NO SMOKING” and
“FLAMMABLE GAS.”



Flame arrestor downstream of the manual
valve.

Verify no ignition sources are closer than 15-ft.
(9 m) to the pipe.



Electrical ground connection with a minimum
3 gauge or heavier stranded copper wire
attached at one end to a ground rod, or other
equally suitable electrical ground. The other
ends of the ground wire should be securely
clipped to both the venting pipe and the vehicle
FMM.



High-pressure electrically conductive
flexible hose approved for CNG.



Manual valve to control gas flow.

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5.4. Defueling Procedure

5.4.2. Defuel Nozzle Operation

This procedure applies to vehicles equipped with a
NGV1-style defuel receptacle.

Hexagon® Agility® p/n 20110011 is a complete fuel
transfer hose assembly used for Gillig defueling.
Figure 36

e

Only certified CNG technicians may perform fuel
system defueling.

5.4.1. Confirm All Cylinder Valves are Open
Set parking brake and use wheel chocks to block
vehicle tires.

f

At each CNG cylinder to be defueled, verify the
cylinder manual valve is fully open by turning the
valve knob counterclockwise. Figures 24, 32, 33a,
and 33b

d

Only cylinders with open cylinder valves will be
defueled. When cylinder valves are closed,
cylinders are not defueled and remain under full
pressure.

g

b

c

a

Figure 36. Fuel transfer hose assembly, p/n 20110011:
BDN defuel nozzle (a), lever (b), ground wire with clip (c),
approved electrically conductive CNG hose (d), flow valve (e),
fuel dispenser/vent stack nozzle (f), cotter pin (g).

Confirm BDN defuel nozzle is compatible with FMM
defuel receptacle.

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The FMM defuel receptacle (2) is equipped with a
check valve which must be safely bypassed to
perform the defuel process. Figure 37

1

3

4

3
4

9

2

1

Figure 37. FMM operation. FMM (4), 1/4-turn manual shutoff valve
(1), defuel receptacle (2), HP gauge (3).
NOTE: Non-Smart Gauge equipped FMM shown;
Smart Gauge face plate similar.

The BDN defuel nozzle lever (b) contains six brass
inserts (not shown), one of which is placed inside the
FMM defuel receptacle to depress the check valve.
Figure 36

5

7

Figure 39. FMM defueling valves and gauges.
1/4-turn manual shutoff valve (1), HP gauge (3), LP gauge (4),
Manifilter (5), defuel valve (7) bleed valve (9).

5. Open FMM defuel valve (7) by turning
counterclockwise. Figure 40

Verify engine is OFF.

Set parking brake and use wheel chocks to block
vehicle tires.

1. Connect BDN defuel nozzle ground wire clip
(c) to vehicle ground. Figures 36 and 38

c

1
Figure 40. FMM 1/4-turn manual shutoff valve (1) in OPEN/ON
position. NOTE: Non-Smart Gauge equipped FMM shown;
Smart Gauge face plate similar.

Figure 38. Ground wire clip (c) must be connected to ground
on the vehicle

2. Verify other ground wire end is connected to
known ground of fuel dispenser or to vent
stack system. Figure 35
3. Attach defuel hose nozzle (f) (Figure 36) to
fuel dispenser or vent stack defuel receptacle
(Figure 35).
4. Turn FMM 1/4-turn manual shutoff valve (1)
to the OFF/CLOSED position. Figure 37
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6. Slowly open Manifilter bleed valve (9) to
bleed any remaining pressure in the fuel
manifold and defuel lines. Figure 39

12. Install brass insert (j) in defuel receptacle (2).
Figure 44

2

7. Close bleed valve (9) and close defuel valve
(7). Figure 39
8. Remove dust cap from defuel receptacle (2).
Figure 41

2

j
Figure 44. Brass insert (j), defuel receptacle (2).

n

13. Inspect defuel receptacle O-ring removed
at Step 10 for damage. Obtain replacement
from Gillig as necessary.
14. Reinstall O-ring (o) inside defuel receptacle
(2). Use a pick or screwdriver to install if
necessary. Figure 45

Figure 41. Defuel receptacle (2), dust cap (n).

9. Clear any debris or other obstructions from
inside defuel receptacle (2). Figure 41
10. Use a pick or a small screwdriver to remove
O-ring (not visible) from defuel receptacle
(2). Figure 42

2

o

k

2

Figure 45. O-ring (o), defuel receptacle (2).

Verify O-ring (o) is properly seated in defuel
receptacle O-ring groove.

Figure 42. Use a pick (not shown) or small screwdriver (k) to
remove defuel receptacle (2) O-ring (not visible).

15. Verify BDN nozzle (a) valve handle (h) is in
the VENT position (p). Figure 46

11. Remove one brass insert (i) from inside BDN
nozzle (a) lever (b). Figures 36 and 43

a

h
b

i

a

p

Figure 46. Before attaching BDN nozzle (a) to defuel receptacle,
verify valve handle (h) is turned to VENT (p).
Figure 43. Brass insert (i) is located inside BDN nozzle (a)
lever (b).

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16. Retract BDN nozzle (a) lever (b) by pulling
cotter pin (g). Figure 47

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a

a

b

Figure 50. Pull on BDN nozzle (a) gently.

Figure 47. Pull on BDN nozzle (a) cotter pin (not visible) to retract
lever (b).

17. Pull BDN nozzle (a) receiver (s) back. Figure
48

a

21. Turn FMM 1/4-turn manual shutoff valve (1)
to the ON/OPEN position. Figure 38
22. Turn defuel BDN nozzle (a) valve handle (h)
to DEFUEL position (m) . Figure 51

a

m

h
Figure 51. Turn BDN nozzle (a) valve handle (h) to DEFUEL
position (m).

s
Figure 48. BDN nozzle (a), receiver (s).

18. Gently slide BDN defuel nozzle (a) on FMM
defuel receptacle (2). Figure 49.

a
2

23. Slowly open fuel dispenser / vent stack
system valve manual handle. Figures 35 and
52
Adjust fuel dispenser / vent stack
system manual valve for a slow,
steady fuel flow to minimize
possibility of fuel system icing.

q

b

Figure 49. BDN nozzle (a), lever (b), FMM defuel
receptacle (2).

19. Carefully depress BDN nozzle (a) lever (b)
until it clicks. Figure 49
20. Gently pull on BDN nozzle (a) to confirm
positive engagement. Figure 50

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Figure 52. Always open defuel valve manual handle (q)
slowly.
NOTE: Fuel dispenser defuel valve shown.

24. Monitor FMM HP gauge (3) to determine fuel
pressure remaining in the fuel system. Figure
39
25. When FMM HP gauge (3) reads zero psi/bar
(Figure 3), slowly open Manifilter bleed valve
(9) in the FMM to bleed any remaining
pressure in the fuel system. Close bleed
valve (9). Figure 39

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26. Close FMM defuel valve (7) by turning
clockwise. Figure 40
27. Remove BDN defuel nozzle from defuel
receptacle. Figure 50
28. Remove BDN nozzle static ground clamp
from vehicle. Figure 38
29. Turn FMM 1/4-turn manual shutoff valve (1)
to the CLOSED/OFF position. Figure 37
30. Use a pick or small screwdriver to remove
the O-ring (not shown) from inside the defuel
receptacle. Figure 42

5.5. Removing CNG Cylinders from Service
All traces of flammable vapor must be removed from
cylinders before disposal to prevent the possibility
of an explosion.

CNG cylinders have a pre-determined service life;
this date is printed on the “Do Not Use After” label
on each cylinder. Contact Hexagon® Agility® for
proper disposal procedures.

31. Gently remove one brass insert (not shown)
from defuel receptacle and replace brass
insert in the BDN check valve lever. Figure
44
32. Inspect defuel receptacle O-ring for
damage. Obtain replacement from Gillig as
necessary.
33. Reinstall defuel receptacle O-ring using a
pick or small screwdriver. Figure 42
Verify O-ring is seated properly in defuel
receptacle groove.
34. Reinstall dust cap on defuel receptacle (2).
Figure 41
35. Defueling is completed; turn FMM 1/4-turn
manual shutoff valve (1) to the OPEN/ON
position. Figure 40
If the above defueling method is unsuccessful for
the electric solenoid system, refer to Appendix A:
“Special considerations for electric solenoid
cylinder valve fuel system defueling.”

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6. Troubleshooting
The following section covers a variety of potential problems and their respective solutions. The issues addressed
in this section are unique to CNG storage systems; however, issues concerning other onboard systems may
influence or directly cause problems with the CNG storage system.
Table 8. Troubleshooting problems.

Table 9. Trouble solutions.

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Contact
Hexagon Agility
Customer Care

Figure 53. Low-pressure fuel light troubleshooting.

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Contact
Hexagon Agility
Customer Care

Figure 54. Gas leak troubleshooting.

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7. Warranty and Contact Information
Please refer to Warranty Manual, ENP-067, for warranty reimbursement procedures.
For technical support, contact the Hexagon® Agility® Customer Care Group:
+1 833 4 HEX CARE toll free (U.S. and Canada)
[email protected]

Proprietary Statement
The information provided within this manual is proprietary and confidential. All prior versions of this manual,
including updates and revisions forwarded separately, are proprietary. The information provided by Hexagon®
Agility® to its customers and clients is solely for the use of those customers and clients. No portion of this manual
may be reproduced or distributed without express written consent of Hexagon® Agility®. Hexagon® Agility®
reserves the right to utilize the intellectual property contained within this publication as content for any other
publication produced by Hexagon® Agility®.
Portions of this manual were drawn from information provided by Hexagon® Agility® suppliers and have been
used with permission from the relevant parties. All information provided from outside sources is so noted and
credited accordingly.
Hexagon® Agility® gives express consent to Gillig to utilize portions of this manual, or the manual in its entirety,
for the purposes of providing customers and clients of Gillig with information pertaining to the Hexagon® Agility®
CNG fuel storage system as used on Gillig CNG buses with appropriate acknowledgement of copyright.
Any information reproduced by Gillig for their use, or that of their customers and clients, should be drawn from
this manual.

Trademark Notice
Hexagon® is a registered trademark of Hexagon Technology AS. Agility® is a registered trademark of Agility Fuel
Solutions LLC. Trademarks of other manufacturers are the property of their respective companies.
Hexagon Agility
3335 Susan Street
Suite 100
Costa Mesa, CA 92626
USA
www.hexagonagility.com

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Appendix A. Special considerations for electric solenoid cylinder valve fuel
system defueling.
A1. Defueling Method 1: Defuel with Audible Test Method
An audible test verifies electric solenoid cylinder valve function and cylinder depressurization.
This method requires electric power to actuate the electric solenoid cylinder valves.

1. Complete all steps in Section 5.4.2. Defuel Nozzle Operation above.
2. Close valves (circled) on all five cylinders (20) using manual knob (10). Figure A1
INSET A

10
11
20

Figure A1. 25531000 system valve end view shown; other electric solenoid cylinder valve systems similar.
Cylinder (20), electric solenoid cylinder valves (circled).
INSET A: Electric solenoid cylinder valve (11), manual knob (10).

3. Energize all electric solenoid cylinder valves.
To energize the solenoid cylinder valves:
a. Verify OEM vehicle battery disconnect switch is in the ON position. Figure 2
b. Use the defuel switch located inside the rear run box (located behind an access panel in the engine
compartment) to energize the solenoid cylinder valves. Refer to OEM vehicle manual.
4. Confirm all cylinder valve (11) manual knobs (10) are closed. Figure A1
5. Slowly open FMM defuel valve (7), turning it fully counterclockwise to open. Figure A2

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1

7

2
8

Figure A2. Fuel Management Module (FMM) components, front view from below.
1/4-turn manual shutoff valve (1), high-pressure (HP) Manifilter (8), defuel valve (7), bleed valve (9).

6. Use BDN defuel nozzle to defuel the supply line system. Refer to Section above.
7. Once CNG supply lines have been defueled, verify FMM HP gauge (3) reads zero psi/bar. Figure A3