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ASE H1 CNG Engines (Transit Bus) study materials
ASE H1 CNG Engines (Transit Bus) study resources

ASE H1 CNG Engines (Transit Bus) practice questions

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Question 1CNG Fuel System Inspection, Safety, and Service Procedures

On a transit bus CNG fuel system, what is the primary function of the manual shutoff valve at each cylinder?

  1. To meter fuel flow based on engine demand
  2. To vent excess gas overboard during normal operation
  3. To isolate an individual cylinder from the rest of the fuel system for service or in an emergency Correct answer.
  4. To regulate the pressure delivered to the fuel injectors

Explanation

Each cylinder has a manual valve so a single cylinder can be isolated for removal, leak repair, or emergency shutdown without depressurizing the entire system. Pressure regulation and metering are handled by the regulator and injectors downstream.

Question 2CNG Fuel System Inspection, Safety, and Service Procedures

Which component reduces high CNG storage pressure to a lower, controlled pressure before the fuel reaches the injectors?

  1. The coalescing filter
  2. The pressure regulator Correct answer.
  3. The check valve
  4. The burst disc

Explanation

The pressure regulator steps storage pressure down to the working pressure the engine requires. Check valves control flow direction, burst discs relieve overpressure, and filters remove contaminants.

Question 3CNG Fuel System Inspection, Safety, and Service Procedures

A technician must perform maintenance on a CNG fuel line. What is the correct first step in preparing the system for service?

  1. Close the manual shutoff valves and vent/de-pressurize the affected section Correct answer.
  2. Purge the line with shop air while it is pressurized
  3. Disconnect the battery and immediately open the line
  4. Loosen the line fitting slightly to bleed pressure

Explanation

Fuel lines must be isolated at the cylinder valves and the isolated section safely vented and confirmed at zero pressure before any fitting is opened. Never crack a fitting to bleed pressure and never introduce air into a pressurized fuel line.

Question 4CNG Fuel System Inspection, Safety, and Service Procedures

What is the purpose of the burst disc installed on a CNG cylinder valve?

  1. To filter particulate from the gas stream
  2. To provide a controlled pressure relief path if cylinder pressure exceeds a set limit Correct answer.
  3. To indicate when the cylinder needs refueling
  4. To prevent backflow into the fill receptacle

Explanation

A burst disc is a pressure relief device designed to rupture and vent gas if pressure rises above a safe threshold, such as during a fire. It does not filter, indicate fuel level, or control flow direction.

Question 5CNG Fuel System Inspection, Safety, and Service Procedures

CNG is stored on the bus at approximately what pressure when cylinders are full?

  1. About 500 psi
  2. About 10,000 psi
  3. About 3,600 psi Correct answer.
  4. About 1,000 psi

Explanation

Transit bus CNG cylinders are typically filled to a service pressure of about 3,600 psi at a reference temperature. The other values are far outside normal CNG storage pressure ranges.

Question 6CNG Fuel System Inspection, Safety, and Service Procedures

Why must CNG fuel system work areas be equipped with adequate ventilation and gas detection?

  1. Because the fuel is odorless and cannot be detected by smell
  2. Because CNG is a liquid that evaporates rapidly
  3. Because natural gas is heavier than air and pools in low areas
  4. Because natural gas is lighter than air and can accumulate at the ceiling Correct answer.

Explanation

Natural gas (methane) is lighter than air, so released gas rises and can collect near the ceiling. Ventilation and gas detection should account for accumulation at high points, and the odorant is not a reliable sole warning.

Question 7CNG Fuel System Inspection, Safety, and Service Procedures

What personal protective equipment is most important when venting or working around a pressurized CNG line?

  1. Safety glasses with side shields and hearing protection Correct answer.
  2. Leather work gloves only
  3. Chemical splash goggles and a rubber apron
  4. A full-face shield, insulating gloves, and flame-resistant clothing

Explanation

Venting high-pressure gas produces a cold jet and noise, so eye protection against debris and hearing protection are the key PPE. A full-face shield and FR clothing are prudent for some tasks but the venting hazard is primarily pressure and noise.

Question 8CNG Fuel System Inspection, Safety, and Service Procedures

During a routine CNG leak inspection, which method is acceptable for locating a leak on a fitting?

  1. Spray the fitting with soapy water while the engine is running at high idle
  2. Apply an approved leak-detection solution and watch for bubbles Correct answer.
  3. Hold a lit match near the fitting
  4. Listen for a hissing sound only

Explanation

An approved non-corrosive leak-detection solution that bubbles at a leak point is the standard safe method. Open flame is never acceptable, and listening alone is unreliable.

Question 9CNG Fuel System Inspection, Safety, and Service Procedures

A bus arrives with a slow CNG pressure drop overnight but no obvious leak. Which area should be checked first?

  1. The transmission fluid
  2. The fill receptacle check valve and cylinder valve fittings Correct answer.
  3. The alternator output
  4. The engine coolant level

Explanation

A slow pressure loss with the bus parked points to a small leak in the high-pressure path, commonly at the fill receptacle check valve or cylinder valve fittings. Coolant, transmission, and charging systems are unrelated to fuel pressure loss.

Question 10CNG Fuel System Inspection, Safety, and Service Procedures

When replacing a high-pressure CNG fuel line, what must be verified before the system is returned to service?

  1. That the line is painted to match the bus
  2. That the engine idle speed is within specification
  3. That the correct rated line is installed and the system passes a pressure/leak test Correct answer.
  4. That the fuel gauge reads full

Explanation

Replacement lines must match the original pressure rating and the repaired system must be leak-tested before service. Cosmetic, gauge, and idle checks do not confirm fuel system integrity.

Question 11CNG Fuel System Inspection, Safety, and Service Procedures

What is the correct action if a cylinder's manual shutoff valve will not close fully during an emergency?

  1. Force it closed with a pipe extension
  2. Spray the valve with water to cool it
  3. Evacuate and isolate the area and notify emergency responders per facility procedure Correct answer.
  4. Open the valve fully to relieve pressure

Explanation

If a shutoff cannot be closed, the gas cannot be safely isolated, so the area must be evacuated and emergency responders notified per the facility emergency plan. Forcing the valve or opening it further increases risk.

Question 12CNG Fuel System Inspection, Safety, and Service Procedures

A technician notices frost forming on a CNG regulator during operation. What does this most likely indicate?

  1. A normal condition caused by gas expansion cooling Correct answer.
  2. A failed burst disc
  3. A coolant leak into the fuel system
  4. An overfilled cylinder

Explanation

Rapid gas expansion across a regulator absorbs heat and can cause frost, which is a normal effect of pressure reduction. Coolant intrusion, overfilling, and burst discs do not produce this frost pattern.

Question 13CNG Fuel System Inspection, Safety, and Service Procedures

Which document should be consulted to determine the correct torque and sequence for CNG cylinder valve fittings?

  1. The manufacturer's service information for that cylinder and valve Correct answer.
  2. The bus wash schedule
  3. The tire inflation chart
  4. The driver's pre-trip checklist

Explanation

Manufacturer service information provides the specified torque values and procedures for cylinder valve fittings. Other documents do not contain fuel system torque specifications.

Question 14CNG Fuel System Inspection, Safety, and Service Procedures

Why is it important to use only components rated for CNG service when repairing a fuel system?

  1. Because non-rated parts are heavier
  2. Because CNG-rated parts are cheaper
  3. Because non-rated parts may not withstand the high pressure and may embrittle or fail Correct answer.
  4. Because the bus will not start with other parts

Explanation

CNG system components must withstand high pressure and be compatible with natural gas; non-rated parts can fail or be susceptible to embrittlement. Cost, starting, and weight are not the governing reasons.

Question 15CNG Fuel System Inspection, Safety, and Service Procedures

During a cylinder inspection, a technician finds deep gouges and exposed fibers on a composite CNG cylinder. What is the appropriate action?

  1. Remove the cylinder from service and follow the manufacturer's condemnation criteria Correct answer.
  2. Reduce the fill pressure and continue using it
  3. Apply a protective coating and monitor
  4. Sand the area smooth and return to service

Explanation

Damage that exposes fibers or creates deep gouges can compromise cylinder integrity, so the cylinder must be removed from service per manufacturer condemnation criteria. Sanding, coating, or reducing fill pressure does not restore structural integrity.

Question 16CNG Fuel System Inspection, Safety, and Service Procedures

What is the purpose of the check valve at the CNG fill receptacle?

  1. To measure the quantity of fuel added
  2. To regulate fill pressure
  3. To prevent gas from flowing back out of the receptacle after refueling Correct answer.
  4. To filter incoming gas

Explanation

The receptacle check valve allows gas in during filling and prevents backflow out of the receptacle afterward. It does not regulate pressure, filter, or meter fuel.

Question 17CNG Fuel System Inspection, Safety, and Service Procedures

A technician is about to disconnect a CNG fuel line that has been isolated and vented. What should be done before loosening the fitting?

  1. Heat the fitting to loosen it
  2. Confirm zero pressure at the fitting with a gauge and wear eye protection Correct answer.
  3. Cap the line while it is still pressurized
  4. Open the cylinder valve to verify flow

Explanation

Even after venting, the isolated section must be confirmed at zero pressure with a gauge before a fitting is opened, with eye protection worn. Opening the cylinder valve would re-pressurize the line.

Question 18CNG Fuel System Inspection, Safety, and Service Procedures

Which sub-topic best explains why CNG cylinders are often mounted on the roof of a transit bus?

  1. To place the lighter-than-air gas above passenger areas and maximize space Correct answer.
  2. To keep the cylinders cool in summer
  3. To reduce the vehicle's center of gravity
  4. To make refueling faster

Explanation

Roof mounting places the lighter-than-air fuel above the passenger compartment and frees interior space. It does not primarily serve cooling, refueling speed, or lowering the center of gravity.

Question 19CNG Fuel System Inspection, Safety, and Service Procedures

During a pressure test of a repaired CNG system, the gauge holds steady but a soap solution shows small bubbles at one fitting. What does this indicate?

  1. There is still a leak at that fitting that must be corrected Correct answer.
  2. The soap solution is defective
  3. The system is acceptable because pressure held
  4. The gauge is inaccurate

Explanation

Bubbles at a fitting indicate gas escaping, which means the repair is not complete even if the gauge appears steady. The leak must be corrected and retested before service.

Question 20CNG Fuel System Inspection, Safety, and Service Procedures

What is the primary hazard of venting CNG rapidly in an enclosed service bay?

  1. The gas will increase oxygen levels
  2. The gas will freeze the floor
  3. Flammable gas can accumulate and reach an ignition source Correct answer.
  4. The gas will corrode tools

Explanation

Rapid venting releases flammable methane that can accumulate and find an ignition source in an enclosed space. Venting must be done per procedure with ventilation and ignition-source control.

Question 21CNG Fuel System Inspection, Safety, and Service Procedures

A bus with a CNG fuel system is being towed into the shop after a collision. What should be done before any fuel system work begins?

  1. Wash the undercarriage first
  2. Immediately open all cylinder valves
  3. Assess for damage and leaks, isolate the fuel system, and follow the emergency response procedure Correct answer.
  4. Start the engine to check for leaks

Explanation

A collision-damaged CNG system must be assessed for leaks and damage, isolated, and handled per the emergency response procedure before any repair work. Starting the engine or opening valves can worsen a release.

Question 22CNG Fuel System Inspection, Safety, and Service Procedures

Why must a technician avoid using compressed air to blow debris off CNG cylinder valve threads before assembly?

  1. Airborne debris and residual gas can create a hazard and contaminate the sealing surfaces Correct answer.
  2. Compressed air is not available in most shops
  3. It will strip the threads
  4. Compressed air is too cold

Explanation

Blowing air near an open fuel component can disperse residual gas and drive debris into sealing surfaces, creating both a safety and cleanliness problem. Proper cleaning methods protect the seal and the technician.

Question 23CNG Fuel System Inspection, Safety, and Service Procedures

A technician observes that the CNG pressure gauge reads lower than expected after a full fill on a cold morning. What is the most likely explanation?

  1. Gas pressure varies with temperature, so a cold fill reads lower Correct answer.
  2. The regulator has failed
  3. The cylinders are leaking badly
  4. The burst disc has ruptured

Explanation

CNG pressure is temperature-dependent, so a fill performed in cold conditions yields a lower gauge reading than a warm-weather fill. A leak, regulator failure, or burst disc would present with additional symptoms.

Question 24CNG Fuel System Inspection, Safety, and Service Procedures

When performing a leak check on a newly installed cylinder valve, why is it important to check both the fitting and the valve stem area?

  1. Because the valve must be replaced after every check
  2. Because the stem seal is a separate potential leak path from the fitting Correct answer.
  3. Because the stem is always the only leak point
  4. Because the fitting never leaks

Explanation

A cylinder valve has multiple sealing points, including the fitting connection and the stem seal, each of which can leak independently. A complete leak check covers all potential paths.

Question 25CNG Fuel System Inspection, Safety, and Service Procedures

What is the correct way to confirm that an isolated CNG line is safe to open for repair?

  1. Rely on the sound of escaping gas stopping
  2. Verify zero pressure with a gauge on the isolated section and follow lockout/tagout Correct answer.
  3. Open the fitting slowly to check for flow
  4. Wait ten minutes after closing the valve

Explanation

Safe opening requires confirming zero pressure on the isolated section with a gauge and applying lockout/tagout to prevent re-pressurization. Sound, elapsed time, or cracking the fitting are not reliable confirmations.

Question 26CNG Fuel System Inspection, Safety, and Service Procedures

Which property of natural gas makes it necessary to use leak detection methods that can detect small concentrations in air?

  1. It is odorless and colorless in its natural state. Correct answer.
  2. It is heavier than air and pools in low areas.
  3. It is toxic at low concentrations.
  4. It has a strong distinctive odor added at the wellhead.

Explanation

Natural gas is naturally odorless and colorless, so odor alone is not a reliable indicator of a leak. Odorant is added for safety, but reliance on smell is not acceptable for precise leak detection.

Question 27CNG Fuel System Inspection, Safety, and Service Procedures

What is the primary purpose of the manual shutoff valve located on each CNG cylinder?

  1. To isolate the cylinder from the rest of the fuel system for service or emergency. Correct answer.
  2. To automatically vent excess pressure if the cylinder overheats.
  3. To provide a connection point for filling the cylinder.
  4. To regulate the pressure delivered to the engine.

Explanation

The manual shutoff valve allows a cylinder to be isolated from the rest of the fuel system, which is essential for safe service and in emergencies. It is not a pressure regulator or a fill connection.

Question 28CNG Fuel System Inspection, Safety, and Service Procedures

When storing CNG cylinders removed from a bus, which practice is required?

  1. Store them in a closed metal cabinet without ventilation.
  2. Store them horizontally on the shop floor with valves exposed.
  3. Store them upright with valve protection caps installed and secured against falling. Correct answer.
  4. Store them near a heat source to prevent condensation.

Explanation

Removed cylinders should be stored upright with valve protection caps installed and secured to prevent falling and valve damage. Proper storage protects the valve from impact, which could cause a hazardous release.

Question 29CNG Fuel System Inspection, Safety, and Service Procedures

Which component reduces the high cylinder pressure to a lower, usable pressure before the fuel reaches the engine?

  1. The pressure regulator. Correct answer.
  2. The pressure relief device.
  3. The manual shutoff valve.
  4. The fill receptacle check valve.

Explanation

The pressure regulator reduces high cylinder pressure to a lower working pressure for the engine. The other components serve different functions such as filling, isolation, or overpressure protection.

Question 30CNG Fuel System Inspection, Safety, and Service Procedures

A technician must perform a leak check on a CNG system component that cannot be isolated from the cylinder. What is the safest course of action?

  1. Loosen the fitting slightly to listen for a leak.
  2. Vent the entire cylinder to atmosphere before checking.
  3. Spray soap solution on the fitting while wearing a full face shield.
  4. Use a combustible gas detector while the system remains pressurized. Correct answer.

Explanation

When a component cannot be isolated, leak detection must be performed with the system pressurized using a suitable gas detector. Loosening a fitting or venting a full cylinder unnecessarily creates additional hazards.

Question 31CNG Fuel System Inspection, Safety, and Service Procedures

What is the correct procedure for depressurizing a CNG fuel system before repairs?

  1. Close the manual shutoff valves, vent the isolated section, and verify zero pressure with a gauge. Correct answer.
  2. Disconnect the battery and wait ten minutes for the system to bleed down.
  3. Open the manual shutoff valves and allow the engine to run until it stalls.
  4. Crack the highest fitting and allow gas to escape slowly.

Explanation

Depressurization requires isolating the section with manual shutoff valves, venting the trapped gas to a safe location, and confirming zero pressure with a gauge. This ensures the system is safe before any fitting is opened.

Question 32CNG Fuel System Inspection, Safety, and Service Procedures

A technician is replacing a CNG high-pressure line and finds that the new line has a different thread sealant applied at the factory. What should the technician do?

  1. Use the line as supplied, following the manufacturer's instructions. Correct answer.
  2. Apply a thread-locking compound over the factory sealant.
  3. Remove the factory sealant and apply PTFE tape.
  4. Clean the threads and assemble dry.

Explanation

CNG lines must be installed according to the manufacturer's instructions, including any factory-applied sealant. Altering the sealant or assembling dry can cause leaks or contamination.

Question 33CNG Fuel System Inspection, Safety, and Service Procedures

Which inspection finding on a CNG cylinder requires the cylinder to be removed from service immediately?

  1. A missing valve protection cap.
  2. A dent that exceeds the manufacturer's allowable limit. Correct answer.
  3. Light surface dust that wipes off.
  4. A faded label on the cylinder.

Explanation

Dents beyond the manufacturer's allowable limit can compromise cylinder integrity and require removal from service. Other findings may require correction but do not necessarily condemn the cylinder.

Question 34CNG Fuel System Inspection, Safety, and Service Procedures

What is the purpose of the vent line connected to the pressure relief device on a CNG cylinder?

  1. To supply fuel to the engine during normal operation.
  2. To drain condensate from the cylinder.
  3. To route relieved gas safely away from the vehicle and occupants. Correct answer.
  4. To provide a path for filling the cylinder.

Explanation

The vent line directs gas released by the pressure relief device to a safe location away from the vehicle and occupants. It is not used for filling, fuel supply, or drainage.

Question 35CNG Fuel System Inspection, Safety, and Service Procedures

When using a combustible gas detector to check for CNG leaks, what is the correct method?

  1. Spray the area with water first to displace any gas.
  2. Test only at the highest point of the system.
  3. Hold the sensor directly against the fitting and wait for an alarm.
  4. Move the sensor slowly around the fitting and along the line, watching for an increase in reading. Correct answer.

Explanation

A gas detector should be moved slowly near the fitting and along the line to allow the sensor to respond to accumulating gas. Direct contact or testing only at one point can miss a leak.

Question 36CNG Fuel System Inspection, Safety, and Service Procedures

A bus equipped with CNG is involved in a collision and the fuel system integrity is unknown. What is the first action?

  1. Immediately tow the bus into the service bay for repairs.
  2. Disconnect the battery and perform a visual inspection from a safe distance. Correct answer.
  3. Start the engine to check for fuel leaks.
  4. Open the manual shutoff valves to relieve pressure.

Explanation

After a collision, the area should be approached cautiously, the battery disconnected if safe, and a visual inspection performed from a distance before any work. Starting the engine or moving the bus indoors can create ignition hazards.

Question 37CNG Fuel System Inspection, Safety, and Service Procedures

Why must CNG fuel system components be electrically grounded during service?

  1. To prevent the cylinder from corroding.
  2. To ensure the gas detector operates correctly.
  3. To prevent static electricity from igniting a gas release. Correct answer.
  4. To improve fuel economy.

Explanation

Grounding prevents the buildup of static electricity that could ignite a flammable gas mixture during service. It is a safety measure unrelated to fuel economy or corrosion.

Question 38CNG Fuel System Inspection, Safety, and Service Procedures

A technician is pressure-testing a repaired CNG line with nitrogen. What is the correct procedure for setting the test pressure?

  1. Pressurize until the relief valve opens.
  2. Pressurize to the test pressure specified by the manufacturer, using a regulated source and a gauge rated for the pressure. Correct answer.
  3. Pressurize to half the working pressure to be safe.
  4. Pressurize to the maximum working pressure of the system.

Explanation

Pressure testing must follow the manufacturer's specified test pressure using a regulated source and an appropriately rated gauge. Over- or under-pressurizing can be unsafe or inconclusive.

Question 39CNG Fuel System Inspection, Safety, and Service Procedures

During a CNG cylinder inspection, a technician finds that the cylinder's requalification date has passed. What action is required?

  1. The cylinder may remain in service if it passes a visual inspection.
  2. The cylinder should be painted and returned to service.
  3. The cylinder must be removed from service and requalified or replaced. Correct answer.
  4. The cylinder can be used as long as the pressure does not exceed half its rating.

Explanation

CNG cylinders must be requalified at intervals specified by code; an expired requalification date means the cylinder must be removed from service until requalified or replaced. Visual inspection alone does not extend the requalification interval.

Question 40CNG Fuel System Inspection, Safety, and Service Procedures

A technician is diagnosing a CNG system that loses pressure only when the vehicle sits overnight with the manual shutoff valves open. Which component is the most likely cause?

  1. A leaking high-pressure regulator seat. Correct answer.
  2. A leaking fill receptacle check valve.
  3. A clogged fuel filter.
  4. A leaking manual shutoff valve on the cylinder.

Explanation

A pressure loss that occurs only when the manual shutoff valves are open suggests a leak downstream of the valves, such as the high-pressure regulator seat. A fill receptacle check valve or manual shutoff valve leak would typically show different symptoms.

Question 41CNG Storage Cylinders and Fuel Lines

Which document establishes the test interval and inspection criteria for a CNG fuel cylinder installed on a transit bus?

  1. The transit authority's farebox maintenance manual
  2. The engine manufacturer's emissions maintenance schedule
  3. The cylinder manufacturer's published inspection and requalification requirements Correct answer.
  4. The bus operator's daily pre-trip checklist

Explanation

Cylinder inspection intervals, test methods, and condemnation limits are set by the cylinder manufacturer and the applicable requalification standard referenced on the cylinder label. Operator checklists and engine schedules address vehicle operation, not cylinder requalification.

Question 42CNG Storage Cylinders and Fuel Lines

A transit bus CNG cylinder label is unreadable and the requalification date cannot be determined. What is the correct course of action?

  1. Remove the cylinder from service and follow the manufacturer's identification procedure Correct answer.
  2. Stamp the current date on the cylinder and resume service
  3. Reduce fill pressure to 2400 psi and continue operating
  4. Continue in service until the next scheduled brake inspection

Explanation

A cylinder whose label or requalification status cannot be verified is not permitted to remain in service. The manufacturer or an authorized facility must establish identity and test history before the cylinder can be returned to service.

Question 43CNG Storage Cylinders and Fuel Lines

What is the primary reason CNG fuel lines on a transit bus are routed inside a protective conduit or sleeve in the underbody area?

  1. To muffle injector noise
  2. To reduce fuel pressure before it reaches the regulator
  3. To shield the line from abrasion, impact, and road debris Correct answer.
  4. To insulate the line against engine heat

Explanation

High-pressure fuel lines must be protected from mechanical damage that could cause a leak. Conduit or sleeving provides physical shielding in exposed underbody locations.

Question 44CNG Storage Cylinders and Fuel Lines

Which cylinder valve feature is designed to limit the rate of gas release if a fuel line downstream of the valve ruptures?

  1. The fill check valve
  2. The manual shutoff handwheel
  3. The excess flow check valve Correct answer.
  4. The pressure relief device

Explanation

An excess flow valve closes when flow exceeds a set rate, as occurs with a downstream line rupture, limiting gas discharge. The handwheel is for manual isolation, the PRD responds to overpressure or fire, and the fill check valve controls fill direction.

Question 45CNG Storage Cylinders and Fuel Lines

What does a CNG cylinder pressure relief device installed on a transit bus cylinder typically respond to?

  1. Loss of 12-volt electrical power
  2. Elevated temperature or excessive internal pressure Correct answer.
  3. Low fuel level in the cylinder
  4. Excessive downstream flow rate

Explanation

PRDs are designed to vent cylinder contents when temperature or pressure reaches a threshold that could lead to cylinder failure. They are passive thermal/pressure devices and do not depend on electrical power or fuel level.

Question 46CNG Storage Cylinders and Fuel Lines

Which type of CNG cylinder is constructed with a fully wrapped carbon fiber composite over a non-load-bearing liner?

  1. Type 3
  2. Type 1
  3. Type 2
  4. Type 4 Correct answer.

Explanation

Type 4 cylinders use a plastic liner that carries no structural load, with the full carbon composite wrap providing strength. Type 1 is all metal, Type 2 is hoop-wrapped metal, and Type 3 is fully wrapped over a metal liner.

Question 47CNG Storage Cylinders and Fuel Lines

During a visual inspection, which condition on a composite CNG cylinder requires the cylinder to be removed from service?

  1. Minor discoloration of the cylinder label
  2. Light surface dust on the cylinder exterior
  3. Deep gouges or cut fibers in the composite wrap Correct answer.
  4. Faded paint on the cylinder bracket

Explanation

Damage that severs or deeply cuts composite fibers compromises the structural integrity of the wrap and is grounds for condemnation. Cosmetic conditions such as dust, faded brackets, or label discoloration do not affect strength.

Question 48CNG Storage Cylinders and Fuel Lines

After any service work that opens a CNG fuel line, what must be done before the bus is returned to service?

  1. Recalibrate the speedometer
  2. Drain and refill the engine oil
  3. Perform a leak check of the affected joints at operating pressure Correct answer.
  4. Replace all cylinders

Explanation

Any joint that has been disturbed must be proven leak-free at operating pressure before the vehicle carries passengers. Leak detection is the direct verification that the repair is sound.

Question 49CNG Storage Cylinders and Fuel Lines

A transit bus CNG cylinder is approaching its labeled requalification date. Which action is required?

  1. Extend the date if the cylinder looks clean
  2. Continue service until the cylinder fails a leak test
  3. Continue service if pressure has never exceeded 3000 psi
  4. Remove the cylinder from service for requalification or replacement Correct answer.

Explanation

Requalification dates are mandatory limits; the cylinder must be tested or replaced before that date passes. Visual appearance or operating history does not authorize extension.

Question 50CNG Storage Cylinders and Fuel Lines

When replacing a high-pressure CNG fuel line on a transit bus, which component specification must be matched?

  1. The bend radius of the original line only
  2. The pressure rating and fitting type specified for the application Correct answer.
  3. The length of the original line only
  4. The color of the original line

Explanation

Replacement line must equal or exceed the original pressure rating and use compatible fittings to maintain system integrity. Color, length, and bend radius alone do not establish suitability for high-pressure service.