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21 Cards in this Set
- Front
- Back
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Brake System Purpose:
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To safely and efficiently slow the speed of the engine to a complete stop.
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Air Brakes Components: 15 Components
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1. Brakes
2. Front/Rear Brakes 3. Air Compressor 4. Governor 5. Air Dryer 6. Air lines 7. Air Tanks 8. Parking Brakes 9. Brake Pedal (Truddle Valve) 10. Relay Valve 11. Quick Release Valve 12. Brake Cans 13. Gauges 14. Low Air Alarm 15. NFPA/CHP 6-Point test |
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1. Brake System
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Rockwell disc, full air type system, with ABS
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2. Front/Rear Brakes
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Front - Rockwell disc, with automatic slack adjusters, and an ABS sensor on each wheel
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3. Air Compressor
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The air compressor is a dual piston, positive displacement pump. It provides 17.5 CFM at 1250 RPM. It runs continuously when the engine is running; a governor maintains the pressure in the system between 90-120 psi.
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4. Governor
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When the pressure in the system falls below 90 psi the compressor is activated by the governor with the unload mechanism. Circulating cycle: 90-120 psi. Charging cycle: < 90 psi
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5. Air Dryer
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Rockwell/Wabco System Saver 1200. Dessicant material that collects moisture. There is purge valve that release when compressor "cuts-out"
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6. Air lines
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reinforced synflex lines, all lines are color coated to correspond with schematic.
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7. Air Tanks
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3 air tanks each one having 4,400 cubic inches of capacity. The wet tank and primary tank are filled first, until 90 psi is achieved. The secondary tank then fills; and above 90 psi they fill at the same time. Each tank has a 1-way check valve to prevent the air from feeding back into the system. Primary: rear service brakes, anchor brakes, Secondary: front service brakes, pump accessories, air accessories.
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8. Parking Brake
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Spring actuated, mounted on the rear axle brake chambers. Yellow parking brake control handle and warning light are mounted on dash, will apply when air < 40 psi in system.
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9. Brake Pedal
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When the drivers foot is depressed, air comes from the tanks through the truddle valve (dual control - front & rear), then to the relay valve, charging air into the service side of the brake cans. The diaphragm exerts pressure overriding the spring tension, in-turn pushing the rod connected to the slack adjuster rotating the slack adjuster and the power shaft. The power shaft is rotated within the power shaft nut.
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Continued. 9. Brake Pedal
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The power shaft is rotated within the power shaft nut rotates the brake piston outward pushing the pad against the rotor. As the braking action continues the caliper assembly is drawn inward (from the power shaft nut worm gear) on the stationary slide pins and this action brings the outer pad in contact with the rotor. This whole movement acts as equal clamping force from both sides of the calipers.
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10. Relay valves
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Is a piston type valve that delivers and exhaust air rapidly to and from the service side of the brake chamber.
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11. Quick release valve
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A quick release valve is built into the relay valve, when the driver lifts his/her foot from the pedal this increases the brake release time. Federal Motor Vehicle safety standard time is set to 1/2 second.
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12. Brake Cans
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Describe the difference between the front and rear.
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13. Gauges
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The pressure gauge is a combination gauge with two needles; red for front supply and white for rear supply. Maximum air pressure is 125 psi. The white needle starts to move after the red needle reaches 80 psi. 1. Rear air pressure warning light is illuminated when the rear air supply pressure (white needle) is < 70 psi. 2. Front air pressure warning light is illuminated when air pressure (red needle) < 70 psi.
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14. Low air alarm
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Audible and visual comes on at 60 psi.
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15. NFPA - 2.12.1: The service brakes shall bring the fully laden apparatus to a complete stop from an initial speed of 20 mph in a distance not exceeding 35' by actual measurement, on a hard, level surface road that is free of loose material, oil, or grease.
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10-3.1.1: The vehicle shall be equipped with an all-wheel antilock braking system if such a system is available from the chassis manufacturer.
10-3.1.2: Service brakes and parking shall be independent and separate systems. All brakes shall be readily accessible for adjustment. 10-3.1.3: The service brake application valve, when applied, shall operate all the service breaks on the vehicle in combination. |
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NFPA continued
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10-3.1.4: Where air-actuated braking systems are provided, they shall include the following: a. An automatic moisture ejector b. An air drier c. A pressure protection valve to prevent the use of all air operated accessories except air operated windshield wipers and air assisting steering, if provided, when the system air pressure drops below 80 psi. d. A quick buildup section in the air reservoir system arranged so that if the apparatus has a completely discharged air system, it is able to move within 60 seconds or start up. The quick buildup section system shall provide sufficient air pressure so that the apparatus has no brake drag and is able to stop under intended operating conditions following the 60 second buildup time.
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Continued. 15. NFPA
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10-3.1.5: Parking brakes shall control the rear wheels, and shall be of the positive, mechanically actuated type. The parking brake system shall hold the fully loaded apparatus on at least a 20% grade.
10-3.1.6: The service brakes shall be capable of bringing the fully laded apparatus to a complete stop from a initial speed of 20 mph, in a distance not exceeding 35' by actual measurement, on a hard, level surface road that is free of loose material, oil, or grease. * All apparatus with a GVWR of 36,000 lbs or greater shall be equipped with air brakes. |
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CHP 6-point brake test
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1. Governor cut in: 88 psi
2. Governor cut out: 110-120 psi 3. Low Air warning: 55-75 psi 4. Emergency & Parking 5. Static: < 2 psi/min 6. Applied: < 3 psi/min |
