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Instructor Bulletin 09-30


September 1, 2009

Dual Air Brake System (DAS) Inspection; Emergency Stopping/Brake System

The purpose of this bulletin is to clarify the Office of School Transportation’s recommendations and the statutorily required procedures for the inspection of the Federal Motor Vehicle Safety Standard (FMVSS) 571.121 Standard No. 121; Air Brake Systems (commonly known as the Dual Air or 121 system). The California Department of Education’s (CDE) Office of School Transportation (OST) has received numerous questions and concerns from the industry regarding the inspection procedures of the Dual Air Brake System. We believe that any confusion or misunderstanding stems from a CDE/OST vehicle air brake system inspection handout that was distributed throughout the transportation industry in 2007. This revised air brake system handout identified the need for the driver to check the Emergency Stopping/Brake System by depleting air from both the front (secondary) and the rear (primary) systems necessitating the spring brake push pull valve engaging (popping out) at all pressures below 60 psi.

The CDE/OST has, and will continue to, conduct extensive research on the proper/required inspection procedures for the Dual Air Brake System with the California Highway Patrol (CHP), Bendix Air Brake Corporation, Federal Motor Carrier Safety Administration (FMCSA), National Transportation Safety Board (NTSB), and the Commercial Vehicle Safety Alliance (CVSA). After a thorough review of all the data, recommendations and opinions provided by these organizations, the CDE has concluded that, in our opinion, when air pressure is lost in one half of the service brake system (in the dual air brake system), the remaining or operating half of the service brake system becomes the “emergency stopping/brake system.” This emergency stopping/brake system is controlled by the service brake treadle valve, which provides appropriate service brake capability for the driver to stop the vehicle in a safe location.

“Emergency brake system operation. The emergency brake system shall be applied and released, and be capable of modulation, by means of the service brake control.” (FMVSS 571-121 Ѕ 5.7.2)

Attached you will find two separate inspections for the Dual Air Brake System. Handout #1 is the California Department of Education’s recommended inspection procedure for the Dual Air Brake System. This procedure adds, in addition to the statutorily required brake system tests, recommended brake system checks, such as: draining air tanks separately and applying the service brake to activate the Emergency Stopping/Brake System. Handout #2 is the statutorily required inspection of the Dual Air Brake System and serves as the minimum test a driver should perform on a vehicle’s Dual Air Brake System.

Questions regarding this instructor bulletin can be directed to the Department of Education’s Office of School Transportation at 916- 375-7100.

Handout #1
California Department of Education
Office of School Transportation

RECOMMENDED FMVSS 121 Dual Air Brake System Inspection/Test

This inspection should be performed on a flat level surface when possible, blocking or chocking the vehicle’s wheels to prevent it from moving may be necessary. Using safe driving procedures, apply the vehicle’s parking brake.

On vehicles equipped with a standard transmission, place the transmission in neutral and disengage the clutch. On vehicles equipped with an automatic transmission, place the transmission in the park position. On vehicles equipped with an automatic transmission that does not have a park position, place the transmission in neutral (blocking the vehicle’s wheels may be necessary).

Note: The emergency stopping/brake system is controlled by the service brake treadle valve, which provides appropriate service brake capability for the driver to stop the vehicle in a safe location.

“Emergency brake system operation. The emergency brake system shall be applied and released, and be capable of modulation, by means of the service brake control.” (FMVSS 571-121 Ѕ 5.7.2)

  1. INSPECTION/TEST. With the vehicle’s parking brake applied, turn on the vehicle’s ignition and start the engine. Build up the brake system air pressure. (13 CCR 1215 [b] Vehicle Condition)
  2. CUT-OUT. When the air governor cut-out pressure is reached, note the air pressure (max.130 pounds per square inch [psi]). Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][A] Vehicle Condition) – (13 CCR 1061[b] Air Governor Adjustment)
  3. CUT-IN. Gently apply and release the service brake treadle valve (brake pedal) to allow the air pressure to drop and the air governor to cut-in. Note the air pressure when it begins to rise (min. 85 psi). Allow the service brake system to build back to cut-out pressure.

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][A] Vehicle Condition) – (13 CCR 1061[a] Air Governor Adjustment)
  4. STATIC TEST. Place the vehicle in first or reverse gear if the vehicle is equipped with a manual transmission. If the vehicle is equipped with an automatic transmission, place the vehicle in park or neutral ensuring that the vehicle will not move when the parking brake is released. Stop the engine, and with the service brake released and the parking brake applied, check the pressure gauge(s) for one (1) minute. Note any air pressure drop (a maximum of two [2] psi per minute is allowed).

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][B] Vehicle Condition) – (13 CCR 1245[k][1] Air Leakage Rates)
  5. APPLIED TEST. Release the parking brake and with the service brake treadle valve make a full service brake application. After the gauge(s) stabilize hold for one minute, observing any drop in air pressure (a maximum of three [3] psi per minute is allowed). Note the amount of air pressure required to make a full service-brake system application. If the amount of air pressure changes from day to day it may indicate an air brake system out of adjustment.

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][C] Vehicle Condition) – (13 CCR 1245[k][2] Air Leakage Rates)
  6. LOW AIR WARNING DEVICES (Front Tank). Apply the parking brake. Turn the vehicle’s ignition on, but do not start the vehicle’s engine. Drain the air in the front (secondary) service brake system by opening the air valve until the low-air-pressure warning devices activate (they must activate at no lower than 60 psi). Note the air pressure the warning devices activate. When draining air from the front (secondary) service brake system, air in the rear (primary) service system should remain intact. Loss of air in the rear (primary) service brake system may indicate a faulty check valve.

    Note: A test of the low air warning devices is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][D] Vehicle Condition) – (49 CFR 571.121.S5.1.5 Warning Signal) – (VC 26506[a] Warning Devices)
  7. EMERGENCY STOPPING/BRAKE SYSTEM (Front Tank). Remove the wheel blocks or chocks if used. Continue to reduce the air pressure to zero (0) psi. The two-way (double) check valve will seal the front (secondary) service brake system, preventing air from escaping from the rear (primary) service brake system. Start the vehicle’s engine, place the vehicle’s transmission in gear, release the parking brake and immediately move the vehicle at a slow speed. Activate the emergency stopping/brake system by applying the service brake treadle valve and the vehicle should stop. The system should have rear (primary) service brakes only. Apply the parking brake and if necessary replace wheel blocks or chocks. (13 CCR 1215 [d][12][E] Vehicle Condition) – (49 CFR 571.121.S5.7 Emergency Brake System for Trucks and Buses) – (VC 26508 Emergency Stopping System)
  8. LOW AIR WARNING DEVICES (Rear Tank). Close the air valve in the front (secondary) service system. Allow the air brake system to build to at least 100 psi. Stop the vehicle’s engine, leaving the ignition in the on position. Drain the air in the rear (primary) service brake system by opening the air valve until the low-air-pressure warning devices activate (they must activate at no lower than 60 psi). Note the air pressure the warning devices activate. When draining air from the rear (primary) service brake system, air in the front (secondary) service brake system should remain intact. Loss of air in the front (secondary) service brake system may indicate a faulty check valve.

    Note: A test of the low air warning devices is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][D] Vehicle Condition) – (49 CFR 571.121.S5.1.5 Warning Signal) – (VC 26506[a] Warning Devices)
  9. EMERGENCY STOPPING/BRAKE SYSTEM (Rear Tank). Remove the wheel blocks or chocks if used. Continue to reduce the air pressure to zero (0) psi. The two-way (double) check valve will seal the rear (primary) service brake system, preventing air from escaping from the front (secondary) service brake system. Start the vehicle’s engine, place the vehicle’s transmission in gear, release the parking brake and immediately move the vehicle at a slow speed. Activate the emergency stopping/brake system by applying the service brake treadle valve and the vehicle should stop. The system should have front (secondary) service brakes and rear (primary) service brakes that are applied by modulated release of air from the spring brake chamber. Apply the parking brake and close the rear (primary) service brake system air valve. (13 CCR 1215 [d][12][E] Vehicle Condition) – (49 CFR 571.121.S5.7 Emergency Brake System for Trucks and Buses) – (VC 26508 Emergency Stopping System)
  10. PARKING BRAKE. Allow the brake system air pressure to build to at least 100 psi. Place the vehicle’s transmission in low gear, release the parking brake and slowly drive the vehicle forward a short distance. Apply the parking brake and the vehicle should stop. (VC 26451[a] Parking Brake System)
  11. SERVICE BRAKE. Make at least two (2) stops by applying the service brake treadle valve to test the operation of the service brake system before transporting passenger(s).

    Note: This test is recommended to be performed daily by the driver for each vehicle driven. (CHP HPH 82.7 Annex B [2][r])
Handout #2
California Department of Education
Office of School Transportation

REQUIRED FMVSS 121 Dual Air System Inspection/Test

This inspection should be performed on a flat level surface when possible, blocking or chocking the vehicle’s wheels to prevent it from moving may be necessary. Using safe driving procedures, apply the vehicle’s parking brake.

On vehicles equipped with a standard transmission, place the transmission in neutral and disengage the clutch. On vehicles equipped with an automatic transmission, place the transmission in the park position. On vehicles equipped with an automatic transmission that does not have a park position, place the transmission in neutral (blocking the vehicle’s wheels may be necessary).

Note: The emergency stopping/braking system is controlled by the service brake treadle valve, which provides appropriate service brake capability for the driver to stop the vehicle in a safe location.

“Emergency brake system operation. The emergency brake system shall be applied and released, and be capable of modulation, by means of the service brake control.” (FMVSS 571-121 Ѕ 5.7.2)

  1. INSPECTION/TEST. With the vehicle’s parking brake applied, turn on the vehicle’s ignition and start the engine. Build up the brake system air pressure. (13 CCR 1215 [b] Vehicle Condition)
  2. CUT-OUT. When the air governor cut-out pressure is reached, note the air pressure (max. 130 pounds per square inch [psi]).

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][A] Vehicle Condition) – (13 CCR 1061[b] Air Governor Adjustment)
  3. CUT-IN. Gently apply and release the service brake treadle valve (brake pedal) to allow the air pressure to drop and the air governor to cut-in. Note the air pressure when it begins to rise (min. 85 psi). Allow the service brake system to build back to cut-out pressure.

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][A] Vehicle Condition) – (13 CCR 1061[a] Air Governor Adjustment)
  4. STATIC TEST. Place the vehicle in first or reverse gear if the vehicle is equipped with a manual transmission. If the vehicle is equipped with an automatic transmission, place the vehicle in park or neutral ensuring that the vehicle will not move when the parking brake is released. Stop the engine, and with the service brake released and the parking brake applied, check the pressure gauge(s) for one (1) minute. Note any air pressure drop (a maximum of two [2] psi per minute is allowed).

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][B] Vehicle Condition) – (13 CCR 1245[k][1] Air Leakage Rates)
  5. APPLIED TEST. Release the parking brake and with the service brake treadle valve make a full service brake application. After the gauge(s) stabilize hold for one minute, observing any drop in air pressure (a maximum of three [3] psi per minute is allowed). Note the amount of air pressure required to make a full service-brake application.

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][C] Vehicle Condition) – (13 CCR 1245[k][2] Air Leakage Rates)
  6. LOW-AIR WARNING DEVICES. Apply the parking brake. Turn the vehicle’s ignition on, but do not start the vehicle’s engine. Gently apply and release the service brake treadle valve to allow the air pressure to drop until the low-air-pressure warning devices activate (they must activate at no lower than 60 psi). Note the air pressure the warning devices activate.

    Note: This test is required to be performed daily by the driver for each vehicle driven. (13 CCR 1215 [d][12][D] Vehicle condition) – (49 CFR 571.121.S5.1.5 Warning Signal) – (VC 26506[a] Warning Device)
  7. PARKING BRAKE. Start the vehicle’s engine and build up the brake system air pressure to at least 100 psi. Place the vehicle’s transmission in low gear, release the parking brake and slowly drive the vehicle forward a short distance. Apply the parking brake and the vehicle should stop. (VC 26451[a] Parking Brake System).
  8. SERVICE BRAKE. Make at least two (2) stops by applying the service brake treadle valve to test the operation of the service brake system before transporting passenger(s).

    Note: This test is recommended to be performed daily by the driver for each vehicle driven. (CHP HPH 82.7)
Questions:   Anna Borges | aborges@cde.ca.gov | 916-375-7100
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