Compressor, Governor & Reservoirs
Not publishedof exam
Compressor Build-UpGovernor Cut-In/OutSafety ValveWet TankCheck Valves
Dual Circuits & Warnings
Not publishedof exam
Primary vs SecondaryGaugesLow-Air WarningReduced Braking
Spring & Parking Brakes
Not publishedof exam
Drag PressureFull Apply RangeCaging SafetyBreakaway Protection
Foundation Brakes & Adjustment
Not publishedof exam
Free StrokeApplied StrokeSlack AdjustersType 30 Chamber
Stopping Distance & Driving
Not publishedof exam
Perception + ReactionBrake LagDowngrade ControlABS Behavior
Pre-Trip & Endorsement Rules
Not publishedof exam
Leakage LimitsGovernor CheckTest FormatRetest Rules
Quick Facts
- Exam
- BC Air Brake Knowledge Test
- Format
- 25 MCQ
- Pass Score
- 20/25 (80%)
- Time Limit
- 45 minutes
- Fee
- $15 per attempt
- Endorsement
- Code 15
- Retest Wait
- 7 days
- Result Validity
- 1 year
- After 3 Fails
- Repeat 7-hr course
Key PSI Checkpoints
60 warns, 85 cuts in, 150 pops off
60 psi warning85 psi cut-in150 psi safety valve125 psi max
Wet Tank vs Service Reservoirs
Wet Tank (Supply)
- Collects water, oil, carbon
- First reservoir after compressor
Service Reservoirs
- Feed primary and secondary circuits
- Protected by check valves
Wet tank collects moisture first
Compressor & Build-Up
- 50 to 90 psi
- Build-up pressure range tested
- 3 minutes
- Max time to build
- 1000-1200 rpm
- Fast idle engine speed
- Compressor
- Supplies compressed air continuously
- Air-over-hydraulic
- Also needs Code 15
- Compressed air
- Higher force than hydraulic
Governor & Safety Valve
- Governor
- Controls cut-in and cut-out
- Cut-out
- 125 psi, stops compressor
- Cut-in
- Before 80-85 psi, restarts
- 105-135 psi
- Typical max range
- 20 psi spread
- Cut-out minus cut-in
- 150 psi
- Safety (pop-off) valve vents
Reservoirs & Check Valves
- Wet tank
- First reservoir, supply tank
- Wet tank job
- Traps water, oil, carbon
- Primary reservoir
- Feeds drive axle brakes
- Secondary reservoir
- Feeds steering axle brakes
- One-way check valve
- Blocks backward air loss
Primary vs Secondary Circuit
Primary Circuit
- Controls drive axle brakes
- Nearest section to pedal
Secondary Circuit
- Controls steering axle brakes
- Backs up primary failure
Primary controls drive axle brakes
Low-Air Warning Response
- Warning activates while driving→Confirms pressure below 60 psi
- Pressure below 60 psi→Stop as soon as safely possible
- Pressure keeps falling further→Spring brakes may begin drag
- Pressure reaches 20-45 psi→Spring brakes fully apply
- One circuit fails only→Other circuit still stops truck
- Reservoir shows 80 psi→Max applied pressure is 80
Dual Circuit Basics
- Primary circuit
- Drive (rear) axle brakes
- Secondary circuit
- Steering (front) axle brakes
- Dual foot valve
- Primary section nearest pedal
- One circuit fails
- Other circuit still brakes
- Reduced braking
- Stop immediately, get service
Gauges & Low-Air Warning
- Low-air warning
- Activates below 60 psi
- 60 psi
- = 414 kPa threshold
- Applied pressure cap
- Never exceeds reservoir pressure
- 80 psi tank example
- Max 80 psi applied
- Dual gauges
- Show primary and secondary
- Warning stays on
- Stop safely, do not drive
Spring Brakes vs Service Brakes
Spring (Parking) Brakes
- Mechanical spring force applies
- Auto-apply at 20 to 45
Service (Foot Valve) Brakes
- Air pressure applies force
- Tested at 90 to 100
Spring brakes park; service brakes stop
Spring Brake Safety Check
- Vehicle must be moved→Cage spring brake chambers
- Before caging any chamber→Block the wheels first
- Parking on a grade→Set parking brake, chock wheels
- Air supply line ruptures→Spring brakes auto-apply instantly
- Relay brakes, no springs→Chock wheels when parked
- Confirming parking brake holds→Gently tug in low gear
Spring Brake Pressures
- Drag begins
- Below about 60 psi
- Full auto-apply
- About 20 to 45 psi
- Spring brakes
- Mechanical spring force, not air
- Mounted
- Rear axles only, typically
- Compounding
- Never combine spring and service
- Breakaway
- Supply rupture auto-applies springs
Parking & Breakaway Rules
- Caging
- Block wheels first, always
- Tractor protection valve
- Isolates trailer air loss
- Relay emergency, no springs
- Must chock wheels parked
- Tug test
- Confirm parking brake holds
- Never use
- Spring brakes as service brake
Stroke Check Order
Pry free stroke first, then apply and hold
0.75 in free defect1.75 in applied defect2 in auto defect
Free Stroke vs Applied Stroke
Free Stroke (Pry)
- Good range 0.5 to 0.75
- Defect over 0.75 in
Applied Stroke (Full)
- Good range 1 to 1.5
- Defect over 1.75 in
Pry method versus full application
Foundation Brake Parts
- Brake chamber
- Converts air to force
- Pushrod
- Transfers chamber force outward
- Slack adjuster
- Lever to s-cam
- S-cam
- Rotates, spreads brake shoes
- Drums/linings
- Friction surfaces that stop
- Brake fade
- Overheated drums lose grip
Manual vs Automatic Slack Adjuster
Manual Slack Adjuster
- Needs periodic manual adjustment
- Applied defect over 1.75 in
Automatic Slack Adjuster
- Self-adjusts during each stop
- Applied defect over 2 in
Manual needs adjusting, auto self-adjusts
Stroke Limits
- Free stroke good
- 0.5 to 0.75 in
- Free stroke defect
- Over 0.75 in
- Applied stroke good
- 1 to 1.5 in
- Applied stroke defect
- Over 1.75 in
- Type 30 auto defect
- Over 2 in stroke
- Type 30 force
- About 3000 lb at 100 psi
Stopping Distance Order
Perceive, react, lag, then brake to stop
0.75 sec perceive0.75 sec react0.4 sec brake lag
Stopping Distance Parts
- Perception time
- About 0.75 second
- Reaction time
- About 0.75 second
- Brake lag
- About 0.4 second (air)
- Total stopping distance
- Perception + reaction + lag + braking
- Hydraulic brakes
- React almost instantly, no lag
Driving Technique Facts
- Downgrades
- Use gear that climbed hill
- Engine retarder
- Auxiliary slowing, saves brakes
- ABS stop
- Apply firm, continuous pressure
- ABS light stays on
- Anti-lock off, brakes work
- Wet brakes
- Apply light pressure, dry them
Leakage Limit Ladder
Three, four, six: single, one-trailer, two-trailer
3 psi single unit4 psi one trailer6 psi two trailers
Single Unit vs Combination Leakage
Single Unit (Class 3)
- Max 3 psi per minute
- No trailer air lines
Combination (1-2 Trailers)
- Max 4 to 6 psi
- More air line volume
More trailers allow more leakage
Pre-Trip Leakage Sequence
- Engine off, brakes released→Watch gauge one full minute
- Single unit, no trailer→Allow max 3 psi drop
- One trailer attached→Allow max 4 psi drop
- Two trailers attached→Allow max 6 psi drop
- Testing applied leakage→Hold full application 90-100 psi
- Any audible leak found→Fail vehicle, needs repair
Exam Facts
- 25 questions
- Total test questions
- 20 correct
- Passing threshold (80%)
- 45 minutes
- Maximum time allowed
- $15
- Fee per attempt
- Code 15
- BC air brake endorsement
- 1 year
- Knowledge test validity
- 7 days
- Standard retest wait
Pre-Trip Leakage Limits
- Single unit (Class 3)
- Max 3 psi per minute
- One trailer combination
- Max 4 psi per minute
- Two trailer combination
- Max 6 psi per minute
- Test pressure
- Full application, 90-100 psi
- Test duration
- One minute, engine off
Pre-Trip Check Steps
- Cut-in check
- Pump to 80% max pressure
- Cut-in confirms
- Rebuilds before 80 psi
- Leak check
- Engine off, listen closely
- Pre-trip required
- Before every day's first trip
- Trip inspection report
- Written report for covered vehicles
Common Traps
Confusing Cut-In With Cut-Out
Cut-in restarts near 80 to 85 ≠ Cut-out stops near 125 psi
Mixing Up Free And Applied Stroke
Free stroke defect over 0.75 ≠ Applied stroke defect over 1.75
Ignoring The Low-Air Warning Light
Means pressure is below 60 ≠ Stop safely as soon as possible
Caging A Spring Brake Unsafely
Always block wheels first ≠ Truck can roll away
Assuming Applied Pressure Exceeds Reservoir
Applied pressure never exceeds reservoir ≠ 80 psi tank caps output
Treating Auto Slack As Maintenance-Free
Manual adjusting can hide problems ≠ Over 2 in needs repair
Shifting To A Higher Gear Downhill
Use the gear that climbed ≠ Never shift up on downgrades
Last Minute
- 1.25 questions, 20 correct required
- 2.45-minute time limit total
- 3.Low-air warning means below 60psi
- 4.Governor cuts in near 85psi
- 5.Safety valve vents near 150psi
- 6.Free stroke over 0.75in needs adjustment
- 7.Applied stroke over 1.75in needs adjustment
- 8.Single unit leakage limit 3psi
- 9.Combination leakage limit 4 to 6psi
- 10.Block wheels before caging springs
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