Number:
Model:

FS-2017-04

Date:__July 28, 2017

All CNG Buses

Model Years:

Approved:

2010 - 2017

Robert L. Birdwell, Executive Director
Quality Control & Field Service

Subject: Pressure Relief Device Vent Tubes & Caps – Agility Bulletin ENP-501
Please read the attached Agility Bulletin, (ENP-501).
The Pressure Relief Device (PRD) vent tube caps are important to maintain to help prevent
Moisture and/or debris from causing the PRD to malfunction.
The bulletin is clear that the existing vent tube caps need not be replaced unless missing
or damaged, but if they are replaced, the PRD vent lines and PRD bodies must be
inspected prior to replacing a cap. The new vent tube caps are red in color to facilitate
visibility, making inspections easier.

RLB:rlb
GILLIG, LLC
451 Discovery Drive
Livermore, CA 94551
(800) 735-1500
(510) 785-1500
BB@Gillig.com

Field Service Bulletin
Maintenance Reminder
Pressure Relief Device Vent Tubes and Caps
ENP-501
Rev. E: May 31, 2017

1. Introduction
Pressure relief device (PRD) vent lines must be capped to prevent moisture and debris
from entering and causing damage to the PRD body. Agility Fuel Solutions installs UVprotected plastic caps over the ends of all PRD vent lines.
The PRD vent tube caps feature heat-activated adhesive which prevents loss from tree
branch strikes, pressure washing, etc. The caps are red to help increase visibility for
inspection.

A. It is important to know and understand that simply replacing PRD vent caps is
not enough to protect the CNG fuel system.
B. A missing cap could be an indication of a leaking PRD.
C. A missing cap allows moisture and debris to enter the PRD vent system, and
may cause damage to the PRD body.
D. When a cap is missing, the PRD vent line and PRD must be inspected for
corrosion, water or debris.
This is not a recall or a service campaign.

2. Affected Units
All CNG vehicle fuel systems. Replace missing or worn PRD vent caps after visually
inspecting the PRD vent lines and PRD bodies.

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Figure 1 Various PRD vent caps. These can be left in place. There is no need to replace
them unless they are missing or damaged.

Figure 2 New red heat shrink PRD vent caps increase visibility. Remember: If a PRD vent
cap is missing or damaged, you must inspect the PRD and vent lines – DO NOT simply
replace the cap.

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3. Corrective Action
1. If a PRD vent tube cap is missing, inspect and remove any water or other
contaminants from the PRD vent tube.
2. Check the PRD body for rust or corrosion. If the PRD body shows signs of rust or
corrosion, the PRD must be replaced.
3. After inspecting and cleaning, replace the PRD vent tube cap.

4. Tools, Parts and Materials
1. Common hand tools
2. Heat Gun with applicable reducing nozzle
a. Ungar 1095 Dual Temperature Heat Gun
b. Milwaukee Dual Temperature Heat Gun 8975-6 with Air Reduction Nozzle
46-80-0297 or Hook Nozzle 49-80-0292
3. Tube de-burring tool, if needed

QTY
DESCRIPTION
AGILITY PART NUMBER
As
PRD vent cap, red, for 3/8-inch and 1/2-inch lines
10712383
needed
Note: The new PRD vent caps replace the old, non-heat shrinkable caps 10702028 (1/2-in.) and
1072030 (3/8-in.)

5. Procedure – PRD Vent Line Inspection and Remediation

Be aware of the live, high pressure lines. Although PRD vent lines carry
zero pressure, the fuel lines contain full cylinder pressure and cannot
be isolated. Verify PRD vent lines by tracing them from the exit at the
top of the system to the opposite end before starting work.
1. If a PRD vent tube cap is missing, perform the following steps.
2. Look for water at the lowest point of the PRD vent line run.
3. A small amount of moisture (condensation) is acceptable, the goal is to remove
standing water which may cause damage to the PRD body at or below freezing
temperatures.
a. In most fuel systems, the PRD vent tube includes a weep hole to drain
moisture out of the vent tube.
i. Check for debris or blockage and clean out the weep hole.

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b. After inspection and any cleaning/draining, replace the PRD vent tube cap.
4. If the PRD vent system is solid tubing (no weep holes), refer to field service bulletin
ENP-584.

6. Procedure – PRD Vent Cap Replacement
1. The PRD vent tubes should be clean, smooth and burr-free. If not, clean and/or
deburr the tubing ends.
2. Insert the cap over the tube end as shown in Figure 3.

Figure 3 Vent cap installed prior to heating.

3. Set the heat gun temperature to “Low.” There is no need to calibrate the
temperature of the heat gun output.
4. The best results are obtained when using a heat gun equipped with a reducer
nozzle. A “hook” accessory is also acceptable, as shown in Figure 4.
5. Make sure the heat gun is always moving as you heat the cap to prevent scorching
and burning the cap or the fuel system cabinet.

Figure 4 Installation using an accessory “hook” nozzle.

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6. Heat until adhesive starts to flow from the edge of the cap. The required
temperature at the surface of the cap is min. 275°F (135°C) to shrink the cap and
activate the adhesive. Figure 5 shows the new PRD vent caps correctly installed.

Figure 5 Correctly installed vent caps.

7. Warranty Information
Replace caps as needed. There is no need to retro-fit any PRD vent caps in the field,
unless caps are missing or damaged as stated above.
Standard repair time (SRT) for his procedure: 0.25 hours.
If you have any questions, contact Agility Fuel Solutions Customer Care at 949-267-7745
or [email protected].
Agility Fuel Solutions | 3335 Susan St Suite 100 | Costa Mesa, CA 92626

Warning Messages Used in this Bulletin

Personal injury or death will occur if procedures are not followed.

Damage to equipment, fuel system or vehicle is possible if instructions are not
followed.
Proprietary Statement

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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 Solutions 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. Agility reserves the right to utilize the intellectual property contained within this
publication as content for any other publication produced by Agility.
Trademark Notice
Agility® and TUFFSHELL® are registered trademarks of Agility Fuel Solutions. Drop-N-Go™ is a
trademark of Agility Fuel Solutions. Trademarks of other manufacturers are the property of their
respective companies.

Revision
-A
B
C

Rev

D

E

Description
Initial Release
Added heat gun details
New part number and pictures for red caps
Added instructions for water removal; revised
company name and address; other minor edits

Desc
Added part number for
the water extraction kit
(syringe), corrected
Figure references.
Make sure to drain all
vent tubes.
Removed closed vent
line procedure and
created a separate
bulletin, ENP-584.

Author

Author
W. Yoshida
W. Yoshida
W. Yoshida

Approved
A. Bhakta
A. Robertson
A. Bhakta

Date
4/29/16
6/9/16
11/21/16

W. Yoshida

A. Bhakta

3/2/17

Approved
3/29/17

W. Yoshida

5/30/17
W. Yoshida

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