Other Parts — Reservoirs, Compressor & Chambers (Chapter 4) +14Quebec · CDL · English

Heavy vehicles have at least three compressed air reservoirs. The supply reservoir receives air from the compressor and feeds two service reservoirs, which supply air to the brake chambers. Trailers/semi-trailers have their own reservoirs supplied by the truck's service reservoirs.

• ✓At least three reservoirs on heavy vehicles
• ✓Supply reservoir receives air from compressor
• ✓Two service reservoirs supply the brake chambers
• ✓Trailers have own reservoirs supplied by truck service reservoirs

If the compressor fails, brakes work for a while, but air supply can run out quickly depending on brake use, accessory air use, and system air-tightness. When it runs low, the low air pressure indicator warns and the emergency brake activates. Pull over and repair immediately.

• ✓Reservoirs store enough air for brakes to work a while after compressor failure
• ✓Air can run out quickly
• ✓Low air pressure indicator warns and emergency brake activates
• ✓Pull over and repair as soon as warning appears

The compressor draws in and compresses outside air and sends it to the supply reservoir. It is engine-driven and operates only when required and the engine runs. Systems maintain a spread of 138 kPa (20 psi). The compressor typically starts below 724 kPa (105 psi) and stops at 862 kPa (125 psi). The pressure regulator manages this.

• ✓Compressor is driven by the engine
• ✓Systems maintain a 138 kPa (20 psi) spread
• ✓Compressor starts when pressure drops below ~724 kPa (105 psi)
• ✓Compressor stops at ~862 kPa (125 psi)
• ✓Pressure regulator starts compressor before 550 kPa (80 psi) and stops it between 805-945 kPa (117-137 psi)

There is a brake chamber near each wheel. Air from service reservoirs pushes a diaphragm attached to a push rod. On drum brakes, the push rod operates a slack adjuster driving a camshaft, and the S-cam clamps the brakes. There are single chambers (service brake) and double chambers (service + parking brake).

• ✓A brake chamber sits near each wheel
• ✓Air pushes a diaphragm attached to a push rod
• ✓Single chamber = service brake only
• ✓Double chamber = service brake + parking brake

Clean air is essential for brake performance. Impurities build up from temperature/environmental changes and must be removed by bleeding reservoirs completely every day using the air bleed valve. In winter, bleed after operating while warm to avoid valves freezing open.

• ✓Bleed reservoirs completely every day
• ✓Use the air bleed valve on each reservoir
• ✓In winter, bleed while vehicle is still warm to prevent freezing
• ✓Still bleed even if an air dryer/purifier is fitted

Most modern heavy vehicles have an air purifier (air dryer/filter) located between the compressor and supply reservoir. It filters, dries and removes impurities from the air, but does not eliminate the need to bleed the reservoirs.

• ✓Located between compressor and supply reservoir
• ✓Filters and dries air, removes impurities
• ✓Does NOT replace the need to bleed reservoirs

Some vehicles (e.g. buses) have an additional emergency air reservoir. If service brakes fail and emergency brakes activate, this reservoir provides air to move the vehicle a few metres from where it stopped.

• ✓Some vehicles (buses) have an additional emergency reservoir
• ✓Allows moving the vehicle a few metres after emergency stop

The driver normally performs the circle check, but the operator may designate another person, in which case the operator becomes accountable.

• ✓The driver must perform the circle check of the vehicle he/she is driving
• ✓A person designated by the operator may perform the check, making the operator accountable
• ✓If the designated person is also the driver, the report must indicate the check was done as the person designated by the operator

When a designated person performs the check, the driver may accept and co-sign it or refuse it and perform a new one.

• ✓If accepting, driver must ensure the check is valid (within previous 24 hours) and co-sign the report
• ✓When accepting, driver is not accountable for the check but must keep the report updated and report trip defects
• ✓If refusing, driver must perform a new circle check and fill out a new report
• ✓Driver behind the wheel must always update the report and record defects observed during the trip

Only tires on weight-bearing axles must be checked (auxiliary lift axle recommended). Check tread groove depth. The tread wear indicator is set at 1.6 mm, found facing the wear indicator marker.

• ✓Defect 9.A (major, steering axle of vehicle GVWR ≥ 4,500 kg): The depth of two adjacent grooves is equal to or less than the tread wear indicator
• ✓Defect 9.1 (minor, all tires): The tread wear indicator touches the roadway or a groove depth is equal to/less than the indicator (1.6 mm)

Check tread and sidewall of all tires for wear, foreign material, damage, and bulging. To detect a flat dual tire, strike it with a hammer. For retreads, a separation 6 mm wide or less is normal. Defect severity differs for a single tire/both duals versus one of the duals.

• ✓Defect 9.B/9.C (major, single tire or both duals): foreign body that could puncture; cut/wear/damage exposing cord or steel belt
• ✓Defect 9.2/9.3 (minor, one of the duals): foreign material that could puncture; cut/wear/damage exposing cord or steel belt
• ✓Defect 9.D (major, all tires): tire touches a fixed component, shows air leak or is flat, or shows a bulge from a carcass defect
• ✓Defect 9.4 (minor): abnormal deformation, or tread/sidewall rubber separated from the carcass

Only tires on weight-bearing axles must be checked (auxiliary lift axle tires recommended). Check groove depth in the tread; the tread wear indicator is set at 1.6 mm, found facing the wear indicator marker.

• ✓Major defect (9.A): on a steering-axle tire of a motor vehicle with GVWR 4,500 kg or more, the depth of two adjacent grooves is equal to or less than the tread wear indicator
• ✓Minor defect (9.1): for all tires, a tread wear indicator touches the roadway or a groove depth is equal to or less than the tread wear indicator

Check the condition of the tire valves on tires around the vehicle.

• ✓Defect 9.5 (minor): The tire valve is worn or damaged (e.g. scraped or cut)
• ✓Inspect valves on tires around the vehicle

List 3 applies to motor coaches; trailers towed are inspected under List 2. Notably, the electric brake system and hydraulic brake system are NOT subject to inspection for motor coaches, while the pneumatic brake system defects fully apply.

• ✓List 3 applies to motor coaches; any towed trailer is inspected under List 2
• ✓Electric brake system (17) and hydraulic brake system (18) are NOT subject to inspection for motor coaches
• ✓Pneumatic brake system defects (19) with standard air leak limits fully apply

For motor coaches, suspension inspection is limited due to accessibility, covering only certain items: air leak with exposed/repaired cord (minor), uncompensated air leak or ball missing/deflated (major), and broken axle/positioning component affecting parallelism (major).

• ✓Motor coach suspension checks are limited to items 14.2, 14.B, and 14.G
• ✓Major (14.B): air leak not compensated by compressor or ball missing/deflated; Major (14.G): broken axle affecting parallelism or wheel position

Because heavy vehicles are dangerous to road workers, the Move-Over Law requires respecting a buffer zone around a stopped vehicle (emergency vehicle, tow truck, or other) when its yellow arrow signal, rotating or flashing lights are activated. Slow down, change lanes to move over as far as possible when safe, and stop if circumstances require.

• ✓Move over around a stopped vehicle with activated warning/flashing lights
• ✓Slow down and change lanes as far as possible when safe to do so
• ✓Stop the vehicle if circumstances require it

Drivers must pay attention to signs near and on road work sites. The speed limit indicated on an orange sign must be observed just as the limit on a white road sign.

• ✓Pay attention to signs near and on road work sites
• ✓Observe the speed limit on orange road-work signs as you would a white sign

When air pressure drops too low for effective service braking, a visual warning (warning light or wigwag), sometimes with a buzzer, alerts the driver. Activation varies by system but is never lower than 380 kPa (55 psi). At 380 kPa it is too low to deactivate the parking brake but enough to keep moving if already in motion.

• ✓Low air pressure warning is never lower than 380 kPa (55 psi)
• ✓Two visual warning types: warning light and wigwag
• ✓At 380 kPa the parking brake cannot be released but the vehicle can keep moving if already in motion

The air pressure gauge measures air pressure in the service reservoirs. Because the system has two independent circuits, there are two gauges (or one gauge with two needles), one per circuit. There is no gauge for the supply reservoir.

• ✓Air pressure gauge measures service reservoir pressure
• ✓Two gauges or one gauge with two needles, one per circuit
• ✓No gauge for the supply reservoir

This gauge measures the compressed air pressure in the brake chambers when the brakes are applied. Unlike the air pressure gauge, it is not a standard feature in heavy vehicles.

• ✓Measures air pressure in the brake chambers when braking
• ✓Not a standard feature on heavy vehicles

Dangerous substances must be labelled using prescribed safety marks. Before taking possession, the driver must verify classification, proper safety marks on containers, and shipper-provided placards.

• ✓Verify the dangerous substances have been classified
• ✓Verify the shipper affixed appropriate safety marks (label, placard or sign) on containers
• ✓Placards must be placed on each end and each side of the vehicle

Dangerous substances are divided into nine classes with recognizable placards: Class 1 Explosives, Class 2 Gases, Class 3 Flammable liquids, Class 4 Flammable solids/self-igniting/water-reactive, Class 5 Oxidizers/organic peroxides, Class 6 Toxic/infectious, Class 7 Radioactive, Class 8 Corrosive, Class 9 Miscellaneous.

• ✓Class 1 Explosives; Class 2 Gases; Class 3 Flammable liquids (flash point ≤ 60.5°C, e.g. gasoline, diesel)
• ✓Class 4 Flammable solids; Class 5 Oxidizers and organic peroxides; Class 6 Toxic and infectious substances
• ✓Class 7 Radioactive; Class 8 Corrosive; Class 9 Miscellaneous products (e.g. PCBs, asbestos)

Class 1 has subdivisions 1.1 through 1.6. Placards are not required for Class 1.4 in certain quantities, and Québec requires special authorization for certain explosives.

• ✓No placards required for Class 1.4 if quantity is 1,000 kg or less
• ✓No placards required for Class 1.4S regardless of quantity
• ✓In Québec, drivers transporting listed explosives must obtain authorization from the Sûreté du Québec

Drivers must always report defects noticed during a trip, being in the best position to detect unusual behaviour.

• ✓Drivers are always responsible for reporting defects noted during a trip, even if a designated person performed the check
• ✓Drivers must be able to carry out an inspection and recognize defects normally detected during a circle check

A circle check must generally be valid within 24 hours prior to driving, with re-inspection rules when not done by a designated person.

• ✓An inspection must be performed within the 24 hours prior to driving; otherwise a new one is required
• ✓If the check was not done by a designated person, the driver must perform a new one even if fewer than 24 hours have elapsed
• ✓Drivers must plan to perform a new circle check before 24 hours have elapsed, except for certain vehicles with different limits

A Class 3 licence authorizes straight-body trucks: double-axle trucks of 4,500 kg or more net weight, or any truck with three or more axles. It covers trucks hitched to trailers under 2,000 kg, or 2,000–4,500 kg carrying permanent equipment, and 2-axle (4,500 kg+) or 3+ axle truck tractors not hitched to a trailer.

• ✓Class 3 permits a double-axle truck of 4,500 kg+ or any truck with 3+ axles
• ✓Class 3 covers hitched trailers under 2,000 kg net weight
• ✓Class 3 covers hitched trailers 2,000–4,500 kg used only for permanent equipment
• ✓Class 3 permits truck tractors (2-axle 4,500 kg+ or 3+ axle) not hitched to a trailer
• ✓Class 3 excludes Class 1 combinations, Class 2 buses, and Class 6 motorcycles

A Class 2 licence authorizes driving a bus designed to carry more than 24 passengers, and a bus hitched to a trailer provided the trailer weighs less than 2,000 kg. Class 2 holders may drive all other categories except vehicle combinations (Class 1) and motorcycles.

• ✓Class 2 permits buses designed for more than 24 passengers
• ✓Class 2 permits a bus hitched to a trailer under 2,000 kg
• ✓Class 2 excludes vehicle combinations (Class 1) and motorcycles

Heavy vehicle drivers must pay attention to signs near and on road work sites. Observe the speed limit indicated on the orange sign just as you would a speed limit on a white road sign.

• ✓Obey the speed limit on orange road work signs as with white signs
• ✓Pay attention to signs near and on road work sites

On a gentle grade you may keep constant speed by accelerating slightly without downshifting. On a steeper grade, use the transmission properly and judge the right moment to downshift for maximum efficiency, especially with a heavy load. To start on an uphill grade, use the service brake to prevent rolling back; when ready, ease off the clutch to the friction point, release the brake, then gradually accelerate.

• ✓On steep grades, time downshifts properly for maximum efficiency, especially with a heavy load
• ✓When starting uphill, use the service brake to prevent rolling backward
• ✓Ease off the clutch to the friction point, release the brake, then accelerate gradually

On a gentle grade you may only need to accelerate slightly. On steeper grades, use the transmission properly and judge the proper moment to downshift for maximum efficiency—especially with a heavy load. To start on an uphill grade, use the service brake to prevent rolling back, then ease off the clutch to the friction point, release the brake, and gradually accelerate.

• ✓On steeper grades, downshift at the proper moment for maximum efficiency
• ✓Proper gear-change timing is especially important with a heavy load
• ✓To start uphill, use the service brake to prevent rolling backward
• ✓Ease off the clutch to the friction point, release the brake, then accelerate

Under the Motor Vehicle Safety Act, wide heavy trailers and semi-trailers must have reflective strips, with limited exemptions.

• ✓All trailers and semi-trailers 2.05 m wide or wider with GVWR of 4,500 kg or more must have reflective strips
• ✓Trailers designed exclusively as a dwelling or office are exempt
• ✓School buses are not required to have reflective strips, but if they do, the strips must be yellow

Reflective strips must be placed in specified locations with prescribed heights and colours around the trailer.

• ✓Upper corners facing rear: at the top, white
• ✓Rear bumper bar horizontal surface, full width facing rear: red and white
• ✓Rear across full trailer width: as horizontal as possible between 375 mm and 1,525 mm from ground, red and white (or solid white/yellow or yellow and white on lower rear/side)
• ✓Each side facing outward, continuous or equally spaced over at least 50% of vehicle length, beginning and ending at the far ends: red and white, yellow and white, solid white or solid yellow

A series of reflectors may replace reflective strips if spaced within the required limits.

• ✓Reflectors may be used instead of reflective strips in some cases
• ✓The centre of each reflector must be no more than 100 mm from the centre of adjacent reflectors

Standards specify location, height and colour of reflective strips: upper rear corners (white, at top), rear bumper bar full width (red and white), rear across full width (red/white or lower-body solid white/yellow), and each side over at least 50% of length.

• ✓Upper rear corners: white, at the top; rear bumper bar: red and white over full width
• ✓Rear across full width and side strips: as horizontal as possible, between 375 mm and 1,525 mm from the ground
• ✓Side strips must run continuous or equally spaced over at least 50% of vehicle length, beginning and ending at the far ends

A permit may authorize: an A double road train (tractor, semi-trailer, tandem-axle single drawbar dolly converting the second semi-trailer to a trailer); a C double road train (tandem-axle double drawbar dolly); a B double road train (semi-trailer resting on a fifth wheel at the rear of the first); or a double road train with a tandem-axle dolly.

• ✓An A double road train uses a tandem-axle single drawbar dolly to convert the second semi-trailer to a trailer
• ✓A C double road train uses a tandem-axle double drawbar dolly
• ✓A B double road train has the second semi-trailer resting on a fifth wheel at the rear of the first

The maximum total loaded mass limit is 67,500 kg. For an LCV consisting of a tractor, semi-trailer and tandem-axle dolly (excluding the second semi-trailer), the total loaded mass must be within regulatory limits for the tractor and semi-trailer plus 2,000 kg.

• ✓The maximum total loaded mass limit for an LCV is 67,500 kg
• ✓For a tractor/semi-trailer/tandem-axle dolly combination, the limit is the tractor and semi-trailer regulatory limits plus 2,000 kg

The tractor must have at least 1 HP per 180 kg of the LCV's total loaded mass. It must also be equipped with an air compressor with a capacity of at least 425 L per minute to supply the brake system.

• ✓The tractor must have at least 1 HP per 180 kg of the LCV's total loaded mass
• ✓The tractor's air compressor must have a capacity of at least 425 L per minute for the brake system

The maximum length of the first semi-trailer is 16.2 m. The minimum length varies: 12 m for a B train and 13.5 m for an A or C double road train.

• ✓The maximum length of the first semi-trailer is 16.2 m
• ✓The minimum first semi-trailer length is 12 m for a B train
• ✓The minimum first semi-trailer length is 13.5 m for an A or C double road train

Road signs in wooded areas warn of wildlife. Animals can venture onto the road and cause serious accidents, especially at night when attracted by headlights. Obey speed limits, be extra careful in areas of reduced visibility (bends, hills, roadside vegetation), and be especially cautious in early morning, dusk and evening, particularly during May, June, October and November.

• ✓Animals are attracted by headlights, so be on guard especially at night
• ✓Obey speed limits and watch areas of reduced visibility
• ✓Be extra careful at dawn, dusk and evening during May, June, October and November

If an animal is on the road, slow down and press your brakes several times to alert motorists behind you. Be alert for other animals nearby. Do not rely on gadgets such as deer whistles, as they have not been proven effective.

• ✓Slow down and press brakes several times to warn following motorists
• ✓Watch for other animals in the vicinity
• ✓Do NOT rely on deer whistles—they are not proven effective

Parking brakes are mounted only on the rear wheels of the tractor/truck/bus (requiring double chambers on at least one axle) and on trailer/semi-trailer wheels (except most auxiliary lift axles). A parking brake is always paired with a service brake and uses a powerful spring that also serves as the emergency brake.

• ✓Parking brakes on rear wheels of tractor/truck/bus
• ✓Requires double brake chambers on at least one axle
• ✓Also on trailer/semi-trailer wheels (except most lift axles)
• ✓Always paired with a service brake
• ✓Powerful spring applies parking brake and activates emergency brake

Pulling the parking brake lever empties air from the parking portion of the double chamber, letting springs relax and apply the brake. Pushing the lever down lets air in, compresses the springs, and releases the wheels.

• ✓Pull lever UP: air empties, springs relax, parking brake applies
• ✓Push lever DOWN: air enters, springs compress, wheels free to turn
• ✓Springs mechanically apply the brake with no air

A service brake is on each wheel. Braking power in air systems comes from compressed air pressure, not the driver's muscle strength (unlike hydraulic systems).

• ✓Service brake installed on each wheel
• ✓Air brake power comes from compressed air, not muscle strength
• ✓Brake pedal lets service reservoir air into chambers

Drum brakes use brake shoes with linings that press against the inside of a drum. S-cam drum brakes are the most common on heavy vehicles; an S-shaped cam pulls the shoes apart. Friction produces heat; overheated linings lose effectiveness.

• ✓Most common brake on heavy vehicles is the S-cam drum brake
• ✓S-shaped cam pulls the brake shoes apart
• ✓Two brake shoes with linings press against the drum
• ✓Overheated linings lose effectiveness

Disc brakes use a disc on the hub with pads held by a caliper that grips both sides of the disc. Common in motor coaches and increasingly on other heavy vehicles. Compared to drum brakes, they use less air (smaller chamber) and resist braking loss at high temperatures.

• ✓Caliper pushes pads against a disc
• ✓Most common in motor coaches
• ✓Consume less air than drum brakes (smaller chamber)
• ✓Less likely to lose efficiency at high temperatures