Heavy truck brakes test
When a truck has no air pressure in its tanks, which warning devices are activated when the
ignition key is turned on?
ANSWER A buzzer, a dash gauge and a red light
What legislation mandates every required standard of a highway truck air brake system?
ANSWER FMVSS 121
If a truck is FMVSS 121 compliant, which of the following air reservoirs must be incorporated
into the air brake circuit?
ANSWER Supply, primary and secondary tanks
In a truck air brake system which sub circuit is primarily responsible for actuating front axle
service brakes when the system is functioning normally?
ANSWER Secondary circuit
When a FMVSS 121 compliant tractor trailer combination is moving down the highway at a
speed of 50 mph, which circuit must be charged with air?
ANSWER Hold off circuit
What best describes the functions of a tractor protection valve?
ANSWER Pressure protects the tractor air supply in the event of loss of pressure in a trailer
Routes trailer supply air and service application signal to the trailer pneumatic circuits
Blocks service signal air to the trailer until trailer air supply is activated
If you have yo make an adjustment to air system cut off pressure where should the adjustment
be made?
ANSWER The governor
, How is the relay section of an FMVSS 121 compliant duel circuit foot valve activated when the
air brake is functioning properly?
ANSWER Pneumatically
What is the function of a quick release gladhand when used?
ANSWER Speeds service brake release timing
What best accounts for brake feel in an air brake system?
ANSWER Resistance of application pressure versus for pressure
What is the potential energy of an air brake system?
ANSWER Compressed air
When a tractor spring brake assembly is charged with air on both its service and hold off
chambers what results is known as?
ANSWER Compounding
What is true about hold off pressure in current truck and trailer air brake systems?
ANSWER Its regulated at 90 psi.
What is the minimum compressed air reservoir volume dedicated to the air brakes required by
an FMVSS 121 compliant highway trailer?
ANSWER 8 times total brake chamber volume
What term is used to describe a truck safety pressure relief valve?
ANSWER Pop off valve
When a truck has no air pressure in its tanks, which warning devices are activated when the
ignition key is turned on?
ANSWER A buzzer, a dash gauge and a red light
What legislation mandates every required standard of a highway truck air brake system?
ANSWER FMVSS 121
If a truck is FMVSS 121 compliant, which of the following air reservoirs must be incorporated
into the air brake circuit?
ANSWER Supply, primary and secondary tanks
In a truck air brake system which sub circuit is primarily responsible for actuating front axle
service brakes when the system is functioning normally?
ANSWER Secondary circuit
When a FMVSS 121 compliant tractor trailer combination is moving down the highway at a
speed of 50 mph, which circuit must be charged with air?
ANSWER Hold off circuit
What best describes the functions of a tractor protection valve?
ANSWER Pressure protects the tractor air supply in the event of loss of pressure in a trailer
Routes trailer supply air and service application signal to the trailer pneumatic circuits
Blocks service signal air to the trailer until trailer air supply is activated
If you have yo make an adjustment to air system cut off pressure where should the adjustment
be made?
ANSWER The governor
, How is the relay section of an FMVSS 121 compliant duel circuit foot valve activated when the
air brake is functioning properly?
ANSWER Pneumatically
What is the function of a quick release gladhand when used?
ANSWER Speeds service brake release timing
What best accounts for brake feel in an air brake system?
ANSWER Resistance of application pressure versus for pressure
What is the potential energy of an air brake system?
ANSWER Compressed air
When a tractor spring brake assembly is charged with air on both its service and hold off
chambers what results is known as?
ANSWER Compounding
What is true about hold off pressure in current truck and trailer air brake systems?
ANSWER Its regulated at 90 psi.
What is the minimum compressed air reservoir volume dedicated to the air brakes required by
an FMVSS 121 compliant highway trailer?
ANSWER 8 times total brake chamber volume
What term is used to describe a truck safety pressure relief valve?
ANSWER Pop off valve
