Air Brake NL (2024)
What is the final factor that will determine if the vehicle will move?
Traction
What is the final factor that will determine if the vehicle will stop?
Traction
How is the heat dissipated, that is generated by the brake?
The heat produced is absorbed by the metal brake drums, which dissipate heat by passing it off into the atmosphere.
if one set of brake shoes are poorly adjust, what effect could it have on the remaining sets of brakes are in the system?
The other wheels would have to do more than their share of breaking that might be more than their break were construct to stand
what is meant by the term friction
friction is the force which resists movement between two surfaces in contact with each other
if the weight of the vehicle is doubled, how many times must the stopping power be increased?
if the speed is doubled, the stopping powered must be double to be able to stop in the same distance
if both weight and speed of the vehicle are doubled, how many time must the stopping powered be increased to be able to stop in the same distance
The stopping power must be increase eight time to be able to stop in the same distance
if the speed of the vehicle is doubled, how many time must the stopping power be increased to be able to stop in the same distance?
the stopping power must be increase four time to be able to stop in the same distance
what is compressed air?
Air squeeze into a much smaller space then that amount of air normally would occupy
what does the abbreviation psi stand for?
pound per square inch
if 40 psi is exerted against a diaphragm of 30 in.² in area, what is the total pounds of force that could be exerted?
1,200lbs
what is meant by brake lag
The time the air takes to travel through a properly maintained air brake system, approximately 4/10 of a second (almost half a second)
what is meant by the following term?
reaction time
The time it takes from the moment the hazard is recognized to the time the break is applied (approximately 3/4 of a second often call thinking time)
what is meant by the following term?
braking distance
The actual distance, the vehicle travels after the brake is applying to the vehicle stop
what is meant by the following term?
stopping distance
stopping distance consist of three factor: driver's reaction time, brake lag, braking distance
what are the five basic components of an air brake system
A compressor, a reservoir or tank, a foot valve, brake chambers and slack adjusters, brake lining, and drum or rotors
what are the two standard main pressure reservoir name
A wet tank and a dry tank
at what pressure should the governor cause the compressor to return to its pumping stage?
when the pressure in the system drops by approximately 20 psi, the governor allow the inlet valve to close, returning the compressor to its pumping stage.
how is a plug air filter likely to affect the compressor?
a dirty filter will restrict the flow of air into the compressor, reducing its efficiency
what cause moisture to form in the brake system?
when the air is compressed, it becomes heated, the heated air cools in the reservoir forming condensation
when is the compressor able to accomplish most of its cooling?
The heated air cools in the reservoir
how are most compressors lubricated?
it is usually lubricated from the engine lubrication system
some are self lubricating and requires regular check of lubricant levels
how often should the main reservoir of drain?
daily
is it necessary to allow all the pressure to escape from the reservoir in order to remove the moisture and sludge which may have accumulated?
allow all air pressure to escape, which will then permit the moisture collected in the tank to drain
what is the maximum pressure available for a full break application at any given time
The safety valve is normally set at 150 psi
what will result if the brake drums are worn, thin or turned too far?
Will build up heat to quickly
if the governor valve failed to unload the compressor, what would be the result?
The safety valve protects the air brake system from an excessive buildup of air pressure
what is the purpose of having more than one reservoir
this give the system a large volume of air in the system
One wet while one dries
what are two functions of the slack adjuster?
means of adjusting the slack or freeplay, in the linkage between the push rod and brake shoe while also changing the movement direction
does the amount of slack in the brake linkage of any affect on the braking efficiency of the vehicle?
yes, If the slack adjusters are not adjusted within the limitations, effective braking is reduced and brake lag time is increased
what is the advantage of keeping the brake chamber pushrod travel adjusted to a minimum travel
ensures there is sufficient pushrod travel to apply full force to the foundation brake under all operating conditions.
what is the most common cause of loss effective braking in an air brake system loss of your pressure or loss of brake adjustment?
it is usually because they are out of adjustment
do automatic slack adjuster on S cam brake required checking
Federal and provincial laws require that manual and automatic slack adjusters be checked daily, during the pre–trip inspection
Can the adjustment on air operated disc brake differ from S cam type brakes?
yes, always check manufactures specification before adjusting
what occurs when drums brakes become overheated?
The brake lining lose their effectiveness
what causes brake fade high temperature?
occurs when the heated drums expand away from the brake lining
what's the main function of the foot valve?
to regulate the flow of compressed air from the reservoir when it is needed for braking
why does the feel of an air operated foot valve differ from an hydraulic brake pedal?
Because air treadle are spring loaded
on what principle does the disc brake operate?
similar to disc brake use in passenger vehicle, air pressure act on a brake chamber and a slack adjuster activating the brake
A common pressure in an air brake system is
from a low 85 to a high 105
what is the compressor minimum pressure set at
20 psi below maximum pressure
how can the driver tells how much air pressure there is in the main reservoir?
looking at his gauges
what must a driver do when a low pressure warning system activate
you must stop and determine the cause
what is the purpose of a quick relief valve?
to allow the breaks to release quickly and fully by discharging the application air near the brake chamber
what is the purpose of a relay valve?
to reduce brake lag by remotely control the brakes at the rear of a heavy truck or semi-trailer in a tractor-trailer combination
what's the purpose of using a larger diameter pipe between the main reservoir tank and the relay valve?
The air line from the foot valve to the relay valve now becomes a control line that signals to the relay valve the amount of air to be drawn from the service reservoir for faster application of the brakes.
if the front axle limiting valve is in the slippery road position, and the foot valve is depressed to make a brake application of 30 psi how much pressure will be applied in front brake chamber
15 psi (50% of rear application)
how is the reservoir protected from overpressurization?
safety valve normally set at 150psi
what stop pressurized air from flowing back into the compressor from the dry tank?
a one way check valve is installed
what pressure will the low pressure warning device activate
below approximately 60 psi
how is brake lag to the rear wheel minimized
A relay valve is install near the rear brake chamber
when should a driver use the front wheel limiting valve?
for better steering control on a slippery road surface
what is meant by compounding the brakes
the combination of two forces; the force applied by the spring brakes and the force applied by the service brake
why are spring brakes a reliable type of parking brake?
can be applied and remain applied without pressure
how are parking brakes held in the release position
during normal, driving air pressure cage does spring, holding it ready for parking or emergency braking
what are the functions of the cab mounted parking brake control valve?
allows the driver to exhaust air out of the parking brake circuit to apply the brakes, or to repressure the circuit to release them.
Will parking brake supply automatically in all braking system
There is a single type of push-pull control valve in use that does not have an automatic release feature.
To apply the parking brakes, the valve must be operated manually, even though the main reservoir pressure has been emptied.
what is the reason for releasing the parking brakes before making full break application test
it could compound the force exerted on the slack adjuster and linkage, which could result in damage or break failure
what's the purpose of an emergency release reservoir tank in the parking brake system?
This is so you can move the vehicle in an emergency. One of the valves is a push-pull type and is used to put on the spring brakes for parking. The other valve is spring loaded in the "out" position.
how can some types of parking brake be released without the use of air pressure
Some spring parking brakes can be released mechanically by "winding them off" or "caging" them. Caging means the brakes are being released.
what is the danger of disassembling a parking brake unit
The springs are under extreme pressure and could cause serious personal injuries
what is the purpose of a two way check valve?
allows the source applying to higher pressure to shift the shuttle so that the higher pressure will be directed to the delivery or service line
why should the glad hand (trailer air hose connector) be protected when not in use?
to prevent the lines from chafing against vehicle components or bouncing off the vehicle
how can a driver control the trailer brake independently?
using the cab mounted trailer supply valve by pushing or pulling the button depending on the type of used
what are three ways of testing the emergency application of the trailer brakes
1- Charge the trailer air brake system, (i.e., build up normal air pressure and push the “air supply” knob in). Shut the engine off. Step on and off the brake pedal several times to reduce the air pressure in the tanks. The trailer air supply control (also called the tractor protection valve control) should pop out (or go from “normal” to “emergency” position) when the air pressure falls into the pressure range specified by the manufacturer (usually within the range of 20 to 45 psi)
2-Charge the trailer air brake system and check that the trailer rolls freely. Then stop and pull out the trailer air supply control (also called tractor protection valve control or trailer emergency valve) or place it in the “emergency” position. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.
3- Check for normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply trailer brakes with the hand control (trolley valve), if so equipped. You should feel the brakes come on. This tells you the trailer brakes are connected and working.
should the hand valve on the tractor-trailer unit be used for parking?
No, the hand valve is NOT to be used for parking
what is the main purpose of the tractor protection valve?
The tractor protection valve prevents air loss from the towing vehicle
what is the main purpose of a trailer supply valve?
The trailer supply valve is usually a push/pull type valve near the driver that supplies air to the trailer's brake system through the supply line
name three functions of the relay emergency valve
1-The relay part of the valve relays air from the trailer reservoir to the trailer-brake chambers during a brake application. It also provides a quick release of the trailer brakes.
2-The emergency part of the valve directs trailer reservoir pressure to the trailer brakes causing an emergency application sometimes referred to as dynamiting.
3-The relay emergency valve has a one-way check valve that stops air in the reservoir from going back to the source of the supply.
describe the function of the supply line
carries air to fill the trailer's tanks
describe the function of the service line
carries pressure for the service brakes
what will occur if the supply line rupture?
a drop of pressure in the supply line between the trailer supply valve and the relay emergency valve will cause the trailer brake to dynamite
what happen if service line rupture?
the escape of air pressure, causing a loss of pressure in the tractor system.
This pressure drop will cause the tractor protection system to close off, exhausting the supply line to the trailer. This will cause the trailer brakes to go into an emergency application.
what will occur if a break application is made with the ruptured service line
Will result in a loss of pressure in the system
if the foot valve and the hand valve operated at the same time, can the application pressure be greater than the reserve or a pressure?
no, the two way check valve allows air to be directed to one delivery pipe from either of two sources. A two-way check valve allows the source applying the higher pressure to shift the shuttle so that the higher pressure will be directed to the delivery or 'service line'.
what is the basic principle of the dual circuit system?
the dual system is two systems or circuits in one. There are different ways of separating the two parts of the system. On a two-axle vehicle, one circuit operates the rear axle and the other circuit operates the front axle.
what valve is used to protect the primary circuit from the secondary circuit?
spring brake modulator valve
in a simple dual circuit system, will the vehicle continue to have braking ability if one circuit failed
If there is an air loss in either circuit, the other circuit will continue to operate independently. Unless air is lost in both circuits, the vehicle will continue to have braking ability
is there a difference between the foot valve used in a single circuit system in the foot valve used in a dual circuit system
The foot valve is similar to the one described earlier in the basic air brake system, but is divided into two sections (two foot valves in one)
name two function of the spring break in a duel circuit system
m
describe the function of the spring break, modulator valve
m
if the trailer breaks away from the tractor on a dual circuit highway system, what applies the brakes on the trailer
The trailer reservoir pressure
The spring breaks
m
what is blended air?
m
can a single circuit trailer be towed with dual circuit tractor?
m
name the component found on an L – 75 system that are not on the dual circuit "highway" system
m
if the trailer breaks away from the tractor on an L – 75 system what applies the trailer brake
The trailer reservoir pressure
The spring break, if equipped
m
what is the maximum time permitted for the compressor to build from 50 psi to 90 psi?
m
what is the maximum pressure loss permitted on a full brake Application with the motor shut off
m
how can the holding power of the trailer brakes be tested?
m
should all driver be able to adjust S cam and drum braking system
m
what is the final brake test that should be made before the vehicle is put into service?
m
what does must be made at the truckstop here sign posted before a steep or long downgrade
m
what are three ways to check the condition of a vehicle braking system?
m
is a brake adjustment part of the air brake test given by motor vehicle department
m
do the brake adjustment specifications differ between S cam, drum system and disc brake system
m
when should the brake be checked after an adjustment has been made
m