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Parts Of An Air-Brake System: Part 5
5.1.14 – Spring Brakes
All trucks, truck tractors and buses must be equipped with emergency brakes and parking brakes. They must be held on by mechanical force (because air pressure can eventually leak away). Spring brakes are usually used to meet these needs.
When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes. A parking brake control in the cab allows the driver to let the air out of the spring brakes. This allows the springs to apply the brakes. A leak in the air brake system, which causes all the air to be lost, will apply the spring brakes.
Tractor and straight truck spring brakes will come fully on when air pressure drops to a range of 20 to 45 psi. Do not wait for the brakes to come on automatically. When the low air pressure warning light and buzzer first come on, bring the vehicle to a safe stop right away while you can still control the brakes.
The braking power of spring brakes depends on the brakes being in adjustment. If the brakes are not adjusted properly, neither the regular brakes nor the emergency/parking brakes will work right.
Multiple-Choice Questions:
Why is spring force used instead of air for emergency and parking brakes?
- All of these are correct
- Springs prevent movement in both directions, air may not
- Air pressure can eventually leak away
- Springs produce more power than air
All trucks, truck tractors and buses must be equipped with emergency brakes and parking brakes. Mechanical force must hold them on because air pressure can eventually leak away. Spring brakes are usually used to meet these needs.
The braking power of spring brakes depends on the brakes being in adjustment. If the brakes are not adjusted properly:
- The regular brakes will work but the emergency/parking brakes will not
- Neither the regular brakes nor the emergency/parking brakes will work right.
- The regular brakes will not work but the emergency/parking brakes will
- Brake adjustment doesn't affect the spring brakes or the emergency/parking brakes
When you want to apply the parking brakes, what does the parking brake control in the cab actually do?
- None of these are correct
- It forces the S-Cam to lock in place, preventing the application of the brakes
- It forces air into both sides of the brake chamber at once and applies the brakes
- It allows the driver to let the air out of the spring brakes. This allows the springs to apply the brakes.
Tractor and straight truck spring brakes will come fully on when air pressure drops to a range of:
- 120 to 150 psi
- 60 to 90 psi
- 20 to 45 psi
- 80 to 110 psi
Which of the following is true about air brakes?
- When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes.
- None of these are correct
- The spring pressure and air pressure combine to release the forces on the brakes, allowing the truck to roll
- When driving, powerful spring brakes are engaged by air pressure. If the air pressure is removed, the springs release the brakes.
If there is a leak in the air brake system and it loses all of its air, what happens?
- The trailer brakes will apply, but the tractor brakes will not
- It will apply the spring brakes
- You will lose your brakes completely
- It will apply the hydraulic brakes
Complete!
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