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Module 6: CNG Depressurizing and Defueling

MODULE 6: OVERVIEW

Introduction There are both planned and emergency reasons for defueling CNG cylinders. CNG fuel
system inspectors must be familiar with defueling methods and must be able to identify
when and how to defuel vehicles when required.

Importance Because defueling can be necessary due to an emergency situation, it is important that
technicians have a plan for defueling vehicles and the proper equipment and training to
perform the procedure.

Module Overview In this module, we will discuss the three most common defueling and fuel reduction
practices:
▪ Fuel reduction strategies
o Vehicle-to-vehicle fuel transfer
▪ Vent-to-atmosphere
▪ Fuel station compressor inlet

Learning Objectives ▪ Determine the circumstances when CNG fuel systems must be depressurized versus
when they must be defueled
▪ Describe generic practices for depressurizing CNG fuel systems
▪ Identify typical defueling equipment and related plumbing
▪ List three main defueling methods

Order of Lessons Lesson 6.1: Depressurize or Defuel
Lesson 6.2: Depressurizing
Lesson 6.3: Reasons for Defueling CNG Vehicles
Lesson 6.4: Required Plumbing for Defueling CNG Vehicles
Lesson 6.5: Safety Practices When Defueling CNG Vehicles
Lesson 6.6: Methods of Defueling

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