CNG Vehicle Conversion and Installation 3

Question 1

What minimum bend radius is generally required for rigid stainless steel CNG fuel tubing to prevent cracking?

Accepted Answer

3 times the outside diameter of the tubing

Answer

A minimum bend radius of 3x the outside diameter prevents work-hardening and cracking in stainless steel CNG tubing.

Question 2

After completing a CNG conversion, which test should be performed FIRST before any operational test?

Accepted Answer

Static leak test at full operating pressure using approved leak detection solution

Answer

A static leak test confirms all connections are sealed before the system is operated, preventing dangerous fuel releases.

Question 3

Which document must a CNG conversion installer provide to the vehicle owner upon completion of the installation?

Accepted Answer

Installer certification label and all applicable cylinder certification documents

Answer

The installer must affix a certification label and provide cylinder documentation including manufacturing date, service life, and pressure rating.

Question 4

CNG cylinders installed in a vehicle's trunk or enclosed cargo area require what safety provision?

Accepted Answer

A pressure relief device vented to the outside of the vehicle

Answer

PRDs in enclosed spaces must vent to the exterior to prevent accumulation of natural gas inside the vehicle if they activate.

Question 5

Which vehicle system component is most likely to require recalibration after a dedicated CNG conversion to maintain proper air-fuel ratio?

Accepted Answer

Engine Control Module (ECM)

Answer

The ECM must be recalibrated with CNG-specific fuel maps because CNG has different stoichiometry and energy content compared to gasoline.

(CNG) Compressed Natural Gas Practice Test