Air Brakes Flashcards
What is max weight on rear axle
9100kg (20,000lbs)
Why air brakes?
They develope a great force to stop a heavy vehicle
Legal height of vehicle ?
4.15metres (13’7”)
Legal width?
2.6m (8’6”ft)
If vehicle is 2x as heavy it will take…
2x as long to stop
If driving 2x as fast it will take
4x as long to stop
If 2x weight AND speed…
8x as long to stop
When checking belt tension
It should not move more than twice the width of the belt
What is compressed air
Air that is squeezed into a smaller space than it normally occupies
Size of reservoir must be..
Big enough to apply the brakes 10-12 times
Normal air brake pressure is
125 psi(862kpa)
How often should you look at the gauges
Frequently
When air leaves the compressor it will be at…
204 degree C
Why is water harmful in reservoir?
Freezes in cold weather
What does an alcohol evaporator do?
Prevent the reservoir from freezing
Compressor must build air pressure from… ___ to ____ in less than ____ minutes at fast idle (1100 rpm’s)
50-90 psi , less than 3 minutes
When compressor stops pumping air it goes into the
Unloading phase
When compressor starts pumping air it goes into the
Loading phase
All air valves do 3 things
Open, close, exhaust
Max air pressure must be between
105-135 psi
Lowest pressure can go before compressor must turn on
80-85 psi
At what pressure will safety valves blow
150 psi
If safety valve blows what is not working properly?
The Governor
What pressure will the low air alarm go off?
60 psi
What to do if low air alarm goes off?
Pull over
Supply line (emergency line) is always…
Under full reservoir pressure and is color coded RED
Service like is only charged with air when
The driver depresses the brake
What color is service line to trailer
Blue
How do you keep supply/service lines/glad hands clean
Hook them together
5 basic components of air brake systems
Compressor, reservoir, foot valve, foundation brakes, air lines
What temp does brake drum START to fail
250 degree c
Max pressure lost on a leak test (single unit)
Can not exceed 3 psi in one minute
Max pressure lost on a leak test (1 trailer)
Can’t lose more than 4psi in one minute
Max pressure lost on a leak test (2 trailer)
Can’t be more than 6psi in one minute
Primary reservoir feed which brakes
Rear drive
Secondary reservoir feed which brakes
Front steer
How many reservoirs in a dual air brake system
Three
Slack adjuster has 3 job
Adjust brakes -10 thou, change pull/push force into torque , Lever (multiplier of force 6:1)
If checking push rod travel
It should not exceed 3/4 of an inch (by hand)
If using 2 people to check push rod travel it should not exceed
Not exceed 1 and 3/4 (by air pressure)
How is the heat dissipated that is generated by breaks?
Absorbed by the brake drums and disappeared into the atmosphere
If one set of brake shoes is poorly adjusted, what effect could it have on the remaining set of brake shoes in the system
They would increase their share of the braking, possibly causing overheating
If 40 psi is exerted againsts a diaphragm of 30 square inches in area, what is the total force that could be exerted
1200 LBS (NOT PSI)
Whst pressure should the governor cause the compressor to return to its loading stage
80-85psi
How often should the reservoir be drained
Daily, or more often during extreme conditions
Signs posted in advance to a downgrade, instructing drivers of trucks to stops inspect their brakes are
Regulatory signs
How are most compressors lubricated today
From the engine lubricsting system
When air pressure in the reservoir is at its maximum the compressor is
Unloaded
If slack adjusted travel is checked while someone makes a brake application, travel should not exceed
1 3/4 inch
If the compressor discharge line is broken, what prevents total loss of air?
The one way check valve
What is the final factor that will determine if the vehicle will move
Traction
What is the main cause of brake fade at high temps
The brake drums expand AWAY from the linings
What is meant by braking distance
The distance the vehicle travels after the brake is applied until the vehicle stops
If a small leak develops in a brake chamber, what valve will continue to hold the same application of the chamber?
Treadle (foot valve)
The main reservoir gauge reads
Pressure available for service
In which direction should the adjusting nut be turned to tighten the brakes
Make the S-Cam shaft rotate in the same direction as an air application
Compressor must build up reservoir pressure with an engine at a fast idle from 50-90psi within
3 minutes
On a long steep downgrade , the best method of descending would be:
Use correct gear and engine retsrder and don’t use brakes
Automatic slack adjuster violation is
2 inches
Which way do you turn an automatic slack adjuster with a HEXAGONAL nut?
Clockwise
Which way do you turn an automatic slack adjuster with a SQUARE nut?
Counterclockwise
Relay valve does 2 jobs
- quick application of brakes
- quick release of brakes
Spring brakes..
Are the opposite of regular brakes
Where would an air dryer be installed in a air brake system
Between compressor and first reservoir
The valve that allows for rapid exhaust at the brake chamber is the
Quick release valve
When should a driver use the manual front wheel limiting valve
When necessary on slippery roads, to reduce front wheel application by 50%
Besides psi, air can also be measured in
kpa
The best way to avoid compounding is
Park brake should be released before a foot brake application is made
The parking brake control valve is usually what color
Yellow
Every carrier you work for must check your driving record
Before hiring you, and once a year after hiring you
The proper technique, when using ABS, is to:
Apply a firm application on the brake pedal and allow ABS to operate
These provide an auxiliary slowing effect and assist the main brake system to slow the vehicle
Retarders
If the service brakes are out of adjustment, the spring brakes will be
Less powerful for parking
The SIX main components of a basic air brake system are:
Compressor, governor, reservoir, air lines, foundation brakes, foot valve
What is the purpose of the spring brake modular valve
Provides controlled rear braking if the primary system fails
The spring parking brake emergency release system will allow the driver to
Move a disabled vehicle to safety
Best way to avoid compounding?
Release spring brake before making a heavy service brake application
On an air brake equipped vehicle , brake adjustment can be check from which location?
When the driver is underneath the truck and trailer
If reservoirs are equipped with automatic drain valves, reservoirs
Should still be drained regularly to check for moisture
To test the holding power of spring brakes, a driver should
Complete a tug test , in low gear, with the spring brake applied
How much pressure should you apply to the foot valve when measuring slack adjustment using the applied stroke method?
90-100psi
Why are drivers required to do a pre trip inspection
It is the law
Following distance in a bus, truck, or heavy vehicle should be no less than
5 seconds
What is the fine for brakes being out of adjustment?
Up to 2,000$
The most common cause of loss of effective braking on air equipped vehicles is
Brakes out of adjustment
What device introduces a small amount of alcohol vapour into the air system
Injectors and evaporators
What are the brake chambers in an air over hydraulic system?
Pressure intensifiers
Whst method of checking brakes do roadside inspectors use
Applied stroke method
What force does the coil spring in spring parking brake chambers exert
1500-2000lbs
The trailer air supply valve must close if the tractor pressure drops below
20 psi
Spring parking brakes will come on when applied by the driver and
If air pressure drops (below 60psi)
Releasing a spring parking brake manually is known as what
Caging
Which of these is an alternative name for the control line
Service line
In dual air brake systems using blended air, the parking brake will take air from
The tank with the highest pressure
Compounding brakes means what
Parking brakes and service brakes applying together
Safety actuator parking brakes will not release if more than how much air has been lost from the parking reservoir?
4 psi
An alternative name for the supply line is what
Emergency line
Spring parking brakes are mounted where on a tractor
On the rear axles
Which of these is a sign that you may have reversed the supply line and service line connections
The spring parking brakes won’t release
Using foundation brakes to hold the vehicle when parked is
Unreliable, illegal, dangerous, all of these
Spring parking brakes will fully apply if air pressure drops to what level?
20-45psi
When trailer brakes “dynamite” they will remain applied for how long?
15 minutes
How are safety actuator parking brakes different from normal brake systems
The brake chamber has two diaphragms
Which of these balances pressure between the service brakes and the spring parking brakes
Spring brake modulator
Spring brakes are kept off by
Air pressure
In color coded systems which colour is used to indicate the control line
Blue
Before manually releasing spring brakes you should do what
Chock the wheels
The chief difference between a trailer air brake system compared to the tractor is that the trailer will not have
A compressor
Operating a vehicle with an excessive brake chamber pushrod stroke can result in a fine up to
2000
By law you must check the manual and automatic slack adjusters
Every day
When you want to apply the trailer brakes without applying the tractor brakes, what should you use?
The hand valve
When checking adjustment you should wear
Hard hat, eye pro, stout clothing
In a type 30 brake chamber, the max available stroke is
2.5 inches
If your vehicle is equipped with an air dryer system, you need to drain the reservoirs..
As often as if the system wasn’t there
When using a bobtail proportioning system braking will require
Higher than usual pedal pressure
A tractor with a bobtail proportioning system will reduce the braking pressure to the drive axle brakes up to
75%
When the trailer air supply valve is closed, the trailer brakes must
Apply fully
If a vehicle is equipped with a tractor parking brake valve, it will usually be what colour?
Blue button
Drum brake linings must be a minimum of Whst thickness
1/4 inch
Alcohol injector systems are designed to prevent
Freezing
Automatic slack adjusters need to be checked
As often as manual adjusters
Brakes need adjustment if the applied stroke is more than
1 3/4 inch
Your vehicle will have automatic slack adjusters if it was built later than
1996
Which of these vehicles are you most likely to find air over hydraulic brakes
A bus
Under what circumstances can you use the hand valve for parking
None of them
The trailer air supply knob on the dashboard will usually be what shape
Octagon
If your vehicle has wedge brakes, you will know the automatic slack adjusters have failed if when the brakes are applied and released the linings move more than…
1/16 of an inch
With brakes on the same axle pushrod travel should be
The same on each side
