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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:
When you want to apply the parking brakes, what does the parking brake control in the cab actually do?
- It forces air into both sides of the brake chamber at once and applies the brakes
- It forces the S-Cam to lock in place, preventing the application of the brakes
- None of these are correct
- It allows the driver to let the air out of the spring brakes. This allows the springs to apply the brakes.
Why is spring force used instead of air for emergency and parking brakes?
- Air pressure can eventually leak away
- Springs produce more power than air
- Springs prevent movement in both directions, air may not
- All of these are correct
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
- 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
- Neither the regular brakes nor the emergency/parking brakes will work right.
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
- You will lose your brakes completely
- It will apply the spring brakes
- It will apply the hydraulic brakes
Which of the following is true about air brakes?
- None of these are correct
- When driving, powerful spring brakes are engaged by air pressure. If the air pressure is removed, the springs release the brakes.
- When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes.
- The spring pressure and air pressure combine to release the forces on the brakes, allowing the truck to roll
Tractor and straight truck spring brakes will come fully on when air pressure drops to a range of:
- 120 to 150 psi
- 20 to 45 psi
- 80 to 110 psi
- 60 to 90 psi
Complete!
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