CNG - Compressed Natural Gas Fuel System Components Questions and Answers

Question 1

Which of the following is the primary function of a thermally-activated Pressure Relief Device (PRD) on a CNG cylinder?

Accepted Answer

To safely vent the cylinder's contents in the event of a fire or high-temperature exposure.

Answer

To regulate the flow of fuel to the engine.

Answer

To prevent over-pressurization during normal fueling by venting excess pressure.

Answer

To act as a manual shut-off valve in an emergency.

Question 2

A technician is servicing a CNG vehicle and notices that after turning the ignition off, the high-pressure fuel supply to the regulator is immediately cut off. Which component is responsible for this action?

Accepted Answer

The main fuel solenoid valve

Answer

The manual shut-off valve

Answer

The fuel pressure regulator

Answer

The check valve at the fill receptacle

Question 3

What is the primary purpose of the check valve located within the CNG fueling receptacle?

Accepted Answer

To prevent the backflow of gas from the vehicle's fuel system.

Answer

To filter contaminants from the incoming gas.

Answer

To regulate the speed at which the cylinder can be filled.

Answer

To measure the pressure of the gas during fueling.

Question 4

A technician needs to replace a damaged section of high-pressure fuel line between the CNG cylinder and the primary pressure regulator. Which material is most appropriate for this application?

Accepted Answer

Seamless stainless steel tubing

Answer

Copper tubing

Answer

Reinforced rubber hose

Answer

Braided aluminum line

Question 5

The main pressure regulator in a CNG fuel system performs which critical function?

Accepted Answer

It reduces the high pressure from the storage cylinders to a much lower, usable pressure for the engine.

Answer

It increases the gas pressure to ensure proper injection.

Answer

It stores a small amount of fuel for cold starts.

Answer

It filters oil and other contaminants from the natural gas.

Question 6

Before performing service on the high-pressure regulator, a technician must isolate the CNG cylinders from the rest of the fuel system. Which component should be used for this purpose?

Accepted Answer

The manual shut-off valve

Answer

The fuel filter

Answer

The pressure relief device (PRD)

Answer

The fueling receptacle check valve