Field Service Bulletin
Pressure Relief Device (PRD) Rubbing Against
Bus System Fuel Cylinders

ENP-247
Rev. B
November 14, 2014

1. Introduction
Abrasion damage to CNG system cylinders has been observed on certain roof mount bus
systems made for NABI Bus, LLC. The abrasion is caused by the pressure relief device
(PRD) repeatedly contacting the cylinder over an extended period of time, see Figure 1.
Agility Fuel Systems has developed a temporary fix that will prevent abrasion damage to
the cylinder that must be installed on fielded units until a permanent solution is available.
Based on our inspection of all buses potentially affected, Agility Fuel Systems
recommends the buses remain in service and this abrasion does not pose an immediate
safety threat. However, it is possible that abrasion over time could cause a gross leak and
possible fire hazard.
The temporary modification must be implemented on all affected systems in the field to
mitigate damage to the cylinder.
1. Reinforced neoprene rubber pads are installed over the PRD to prevent chafing of
the cylinder by the PRD.
2. The PRD must be checked for clearance and corrected if needed.

Figure 1 The PRD location near the cylinder

2. Affected Units
This procedure applies to part number 23905000 (40-foot) and 23906000 (31-foot) Agility
Fuel Systems CNG-fueled buses supplied to NABI Bus, LLC for Dallas Area Rapid Transit
(DART).

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3. PRD Locations

Figure 2 Eight PRD locations, 40-Ft. NABI bus system 23905000

Figure 3 Eight PRD locations, 31-Ft. NABI bus system 23906000

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Figure 4 PRD details

4. Required Parts – Agility 23905000 (40-Ft) and 23906000 (31-Ft)
Systems
ITEM
Bus PRD Rubber Pad Kit
PART NUMBER
20103299
10700008
10700220

PART NUMBER
20103298

QTY
1

DESCRIPTION
PRD Rubber Pad
Hex Cap Screw, 1/4-20 x 2-in., Grade 8,
Steel, UNC, Yellow Zinc
Flange Toplock Nut, 1/4-20, Grade 8,
Steel, Yellow Zinc

QTY
16
16
16

5. Procedure – PRD Orientation (Clocking)

WARNING
Cylinders MUST be isolated, defueled and depressurized for the PRD
being moved before any connections are loosened to prevent serious
injury.
1. Tools Needed for Adjusting PRD Clocking
a. 7/8-in. curved wrench or 7/8-in. crows foot with ratchet
2. The PRD should be roughly equidistant (centered) between cylinders. Defuel the
fuel cylinders and depressurize the system before loosening any connections on the
PRD.
3. Loosen the two fuel line fittings on the PRD body (see Figure 4).

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4. Move the PRD so the PRD and the cylinder is equidistant (centered).
5. Tighten the fittings using a backup wrench to maintain the PRD’s position.
6. Inspect work area, re-pressurize and perform a leak test.

6. Procedure – Rubber Pad Installation
WARNING
Be careful when walking on the stringer beam (frame) members to
minimize flex. Wear the appropriate safety gear, including fall
arrestment harnesses as needed to prevent injury.
1. Tools Needed for Rubber Pad Installation
a. 7/16-In. socket with ratchet or ratcheting wrench.
b. 7/16-in. open end wrench
2. Apply two sheets of reinforced neoprene to the PRD body and use 1/4-20 hardware to
secure the pads to the PRD (see Figures 5, 6, 7 and 8).
3. Use flat washers under the each bolt head and nut.
4. There should be a minimum of 1/8-inch between the rubber pad and the fuel cylinder.

PRD pads are installed on each
side of the PRD. Rubber pads can
touch the fuel cylinder, but PRD
contact to the tank should not be
allowed. Clearance should be at
least 1/8-inch between the rubber
pad and the cylinder.

Figure 5 Pads installed on PRD

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Figure 6 and Figure 7 Views of installed pads on the PRD

Figure 8 Rubber pads over the PRD are held in place with 1/4-20 hardware.

7. Revised Inspection Procedure
Inspect each cylinder, PRD and rubber pads for abrasion and/or damage every five (5)
weeks in addition to the CNG fuel system inspection routine that is normally utilized.
Look for:
a) A minimum of 1/8-inch clearance between the fuel cylinder and the PRD
b) Abrasion to the cylinder or any damage to the rubber pad
1) NOTE: The rubber pad may contact the tank, but there should be no observable
damage to the cylinder

8. Warranty Statement
This procedure is covered under warranty. Standard repair time (SRT) is 0.25 hours per
PRD. Refer to warranty reimbursement procedures in the Warranty Manual, ENP-067.
If you have any questions, contact Agility Fuel Systems Product Support at 949-267-7745
or [email protected].

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Agility Fuel Systems
Product Support
1815 Carnegie Ave
Santa Ana, CA 92705 USA

Proprietary Statement
The information provided within this document is proprietary and confidential. All prior
versions, including updates and revisions forwarded separately, are proprietary. The
information provided by Agility Fuel Systems 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 Agility Fuel Systems. Agility Fuel Systems
reserves the right to utilize the intellectual property contained within this publication as
content for any other publication produced by Agility Fuel Systems.
Revision

Description

Author

Approved By

Date

--

Initial Release

W. Yoshida

Y. Coy

8/22/14

A

General edits
Bolt length 2-in.,
added part numbers

W. Yoshida

Y. Coy

8/26/14

M. Gustafson

Y. Coy

11/14/14

B

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