Chapter 8 Air Breaks Flashcards
Why do we use air breaks as opposed to hydraulics for trucks
- Air breaks use a much greater force to apply the brakes than hydraulic braking systems do, which is needed to cope with heavy loads of commercials vehicles
- Are more tolerant to small leaks, which in brake failure (an air brake system includes a compressor to generate more compressed air as needed)
- Are capable of stopping heavy comercial vehicles safely
What is compressed air
squeezing air into a small space
10psi on 1 sq inch is 10 pounds of air resistance
What is a compressor used in a airbreak
pump air into the air break system
What does a governor do
controls the air compressor so when the reservoir is low it loads air in and when the reservoir is full it stops the discharge valve
what do air lines do
to allow pressurized air to flow between the air brake system components
what does a reservoir do
store compressed air
Brake pedal or foot valve
apply brakes by directing compressed air from the reservoir to the brakes
What are foundation brakes and what are they made up of
including brake chambers, slack adjusters, brake linings and drums or rotors to transfer the force generated by compressed air through a mechanical linkage to apply the brakes.
What is force multipliers
the force generated at the wheel to stop is gonna be greater then the force of you pushing on the brake pedal
How does the air brake chamber help stop the vehicle
It converts the force of compressed air into a strong mechanical force through the push rod and slack adjuster.
what is inside the air brake chamber
a rubber diaphragm in between two steel housing units
What happens when we push our brake pedal down in the braking component
the compressed air opens into the brake chamber pushing on the rubber diaphragm which pushes on the push rod.
What is the most common size air chamber used on trucks
type 30 regular chamber with 30 sq inches of effective diaphragm area. If its a type 15 air break its gonna have 15 sq inch of are and so on.
how much psi to make a normal stop
20 psi or less
What is the foundation brake
mechanical parts of the braking system inside the wheel
What is the most common part foundation brake
s-cam drum brake
What happens after the pushrod is being pushed on with an s-cam brake
pushrod pushes on the leaver arm called a slack adjuster which is connected to a cam shaft shaped like an s which the s-cam to rotate causing the brake lining to press against the brake drum.
What is the slack adjuster and what happens if it isnt adjusted poroperly
it wont properly rotate the scam causing less friction between the the brake lining to the brake drums
what is the purpose of the return spring
to keep the brake linings away from the drum when the air pressure is released from the air chamber
What makes up a basic airbrakes system
Compressor Airlines Reservoir Brake Pedal Foundation Brakes
Air compressor is located where on the truck
Mounted on the engine or the side of the engine as long as the engine is running the compressor will be running
what type of air compressors do all trucks use
piston type air compressors they can have 1, 2 or 4 cylinders depending on vehicle demands
Whats the operating pressure and temperature of a truck air compressor?
120 psi and air temperature of 204 degrees celsius
What two types of cooling systems are used to prevent the compressor from overheating
- Circulating engine coolant through the compressor
- Lighter units use air cooling
What role does oil have in the engine
Lubircation
Why is there an air filter for the compressor
so it only intakes clean air check your filter regularly so it doesn’t get clogged
what does the intake stroke do in the air compressor
piston moves down in the cylinder tit creates a vaccum within the cylinder than the atmospheric pressure outside of the compressor. with the inlet valve open, air is drawn into the cylinder to fill the vaccum
What is a compression stroke in the compressor
When the piston reaches the bottom of the cylinder it begins to rise. closing the inlet valve causing the air to compress as it goes up and the discharge valve opens and the pressurized air goes through the line and into the reservoir
What is the maximum pressure range on vehicles
105 to 135 psi
when do governors stop unloading (stop the compressor from pumping air)
air pressure reaches about 125 psi
what is The range between minimum and maximum
air pressure
approximately 20 psi
For example if you had a reservoir with max psi of 125 at 105 it would restart
What is a reservoir
Steel tank that stores compressed air.
Whats a safety valve and how does it work
A safety valve is a valve on the reservoir that protects the reservoir for being to pressurized if the governor fails to unload, The safety valve contains a spring loaded ball and when becomes to much the pressure would push on the ball pushing air out
Air that come straight from the compressor goes where and what does it do`
It goes to the wet tank and the wet tank is the supply resevoir its used because the initial air coming in has some moisture in it and has small particles of oil in it
What happens if the oil and the moisture build up in the supply reservoir tank and what can you do to prevent this
if you allow all the moisture and oil to build up the sludge will enter other components causing trouble with the valves and in the winter it could cause for lines to freeze up causing malfunction of valve or brake chamber. using the drain valve or drain cocks we can prevent this sludge from building up. Drain the reservoirs daily.
if a reservoir is 80 psi what is the maximum brake application
80 psi
What is a Dual foot valve
a foot foot valve that controls two sections a primary and a secondary. when applied primary sends air to the drive axle brake (closest to the pedal) where secondary sends air to the steering axle brakes.
How many reservoirs are in a dual braking system
3 supply reservoir, primary reservoir and secondary reservoir. if one fails the driver still has enough air to make a safe stop even tho braking power is reduced. both primary and secondary reservoirs are filled by one way lines from the supply reservoir
Why do we have primary and secondary reservoirs
so brake components won’t be contaminated directly throught the supply reservoir and to divide the air so the brakes can be applied quicker
What is a One way check valve
a valve that only has air coming one way this way if failure happens in one of the reservoirs it wouldnt be able to flow back and suck all the other air out from the rest of the system
what are the purposes for reservoir pressure gauges
its an instrument used to read how much psi of air is in each reservoir
how often should you check your reservoir gauges
Constantly to make sure there is enough or no problems so you can also see how much stopping force you have
At how many psi’s must you have dropped to in order for the low air warning to come on
60 psi
What is a wig wag
a wig wag is an older method of the low air warning its an arm that extends out when your system is lower then 60 psi
what should you do if a low pressure warning comes on
pull over and find the source of the leak or problem regarding the low air right away
What is a quick release valve and what are its uses
The quick release valve is used to empty out air at the source of the brakes so it doesn’t have to travel back to the foot valve to be released so there wont be no brake lag.
What is a relay valve used for?
Relay valves are used to reduce the lag time when you apply brakes. a control line and a supply line are both connected to the relay valve but when you press the brake the control line pushes on the relay valve pushing air to the brakes. Relay valves can handle the volume requirements for 2 to 4 air chambers. usually found on rear axle brakes but sometimes steering brakes.
Parking with your air brakes
IS ILLEGAL becuase if you lose air your truck will roll away
What are the names of the 2 parking brakes
Spring Parking Brake
Safety Actuator
Spring Parking Brakes contain
They have another chamber that has a big spring coil that if turned on pushes down the parking brake releasing the air from that compartment
Where are spring parking Brakes located
They’re located on rear axles only
If air pressure falls what happens to the spring parking brakes
They will begin to stop the vehicle
Spring brake parking brakes and leaking
if the spring brake parking brake begins to leak they’ll slowly begin to apply at 90 p.s.i or higher
Apply or releasing spring parking brakes
- Normally applied and release by using the parking brake control valve on the dash board
- if the air pressure in the system falls below approximately 60 p.s.i the springs will begin to drag and at 20 to 45 psi it will be fully applied
What is a parking brake control valve
It is a valve that controls the parking brake pushing the button in will release the parking brake sending air into the chamber parking chamber. Pulling it will pull air into the chamber applying the brakes (see page 160 for diagram)
What is compounding brakes and what damages can it do
Compounding brakes is when you have the service brake applied and your spring brake (parking brake). This can damage slack adjusters, s-cams, brake chambers mounting bolts brake shoe rollers, shoes and brake drums
What is caging your brakes
When you use a caging bolt to release the spring brake so your vehicle can freely move around if you have no air ALWAYS block your wheels. ONLY use in emergency
What determines the effectiveness of the spring brake
how often you adjust them
whats a two way check valve
a valve that takes air from both the primary and secondary reservoir and which ever reservoir has the strongest psi is where i get its air. used for emergency situation if there is a leak in one line the other can supply air for the parking brake. air from these valves is known as blended air
Spring Brake Modulator
If there is a loss of pressure from the primary reservoir this module detects that and applies the spring brake in accordance to how much the service brake is being applied to help with a controlled even stop
what is Safety Actuator parking brake
its a one way locking tube that pushes out a push rod but its prevented from pushing back in by a locking mechanism.These do not apply automatically only loss of pressure in the parking reservoir causes them to apply
what 2 lines are necessary for a tractor trailer air break system and what do they do
Supply line(emergency line) Sends air to the trailer reservoirs (red) Control line(Service line) sends air as control signals (blue)
What do all trailers need
Emergency stopping brakes if the trailer ever disconnects from the tractor
What is a Relay emergency valve
if the trailer isn’t equipped with spring brakes brakes and if the trailer senses it disconnects it will apply with its own reservoir this is called dynamiting page 165 - 166 for visuals
How long should emergency brakes be applied for on a trailer that broke off
15 minutes minimum
what do Trailers with spring breaks have
they have relay valve and a trailer spring brake valve that fills the reservoir and controls the spring parking brakes pages 167 and 168
Why do we perform tug tests
we perform tug tests to feel if trailer brakes are working
what is the Tractor Protection system
its system in place to protect the tractor from losing all air when the trailer breaks off this is protected by trailer air supply valve and tractor protection valve.
what does the Trailer air supply valve do
this controls to shut on and off the air going into the valve
What is the Hand Valve
is used to only manage trailer brakes Do not use this for parking. this is only meant to be used for coupling
What is bobtailing
Bob tailing is when you drive a tractor without a trailer attached
What is the bobtail proportioning system and why is it used
helps prevent unwanted lock up from the rear wheels when bob tailing using different valves decreasing drive axle brakes by 75% preventing the back brakes from locking up. Steering axles will apply more pressure to stop at proper distances.
