Air Brake Controls

Tractor protection valves:

protect a tractor air system in the event of a trailer breakaway

may not activate until air pressure drops to 20-45 PSI

are signaled from a dash valve

all of the above

Correct! Wrong!

A wig-wag (low air warning device) should operate:

between 20-45 PSI

when pressure drops to 60 PSI

when the vehicle is shut off

at air governor cut-in pressure

Correct! Wrong!

An inversion/spring brake modulating valve must be mounted upside down.

True

False

Correct! Wrong!

The Canadian Motor Vehicle Safety Standards (CMVSS) schedule 121 states that parking brakes must hold an empty or loaded vehicle on a:

12% grade

20% grade

30% grade

40% grade

Correct! Wrong!

Spring brakes commonly operate the _________________ to keep the vehicle from moving when parked.

regular service foundation brake assembly

drive shaft type parking brake assembly

special wheel brake assembly

none of the above

Correct! Wrong!

Cracking pressure" of relay valves refers to:

the pressure required to split the valve

the pressure required to first open the passage from the reservoir port to the delivery post

the pressure required to first open the passage from the valve to the exhaust port

the pressure required to first open the passage from the foot valve to the delivery port

Correct! Wrong!

Which section of the foot valve is used as the primary section?

Next to the foot pedal

Away from the foot pedal

Either A or B

Refers to the leading brake shoe

Correct! Wrong!

The CMVSS section 121 states that a visual low air warning device must be located in the drivers forward field of vision.

True

False

Correct! Wrong!

What is the style of valve often called a "highway valve"?

Single check valve

Double check valve

Hand valve

Foot valve

Correct! Wrong!

On a dual air system, a tractor protection valve uses which of the following?

Supply air

Blended air

Primary air

Foot valve

Correct! Wrong!

An ideal air braking system can be defined as:

one in which braking forces are proportional on all axles

one in which the braking pressure reaches each brake actuator simultaneously and at the same pressure level

one in which each axle receives braking force in a sequential manner, starting with the closest axle to the governor

one in which each wheel receives a graduated braking force over a preset range of the most probable braking conditions

Correct! Wrong!

All of the following could cause excessive leakage in an air brake system (service brakes applied) EXCEPT:

a leaking brake chamber diaphragm.

a leaking hose, tube, or fittings.

applying spring brakes.

a bad relay valve.

Correct! Wrong!

If the load and speed of a unit are both doubled, the effort needed to stop is _________ times.

2

4

6

8

Correct! Wrong!

Where would you expect that a quick-release valve would be mounted?

Close to the brake chambers

In the cab, close to the trailer protection valve

On the dash next to the tractor push pull valve

On the outside backwall of the tractor next to the gladhands

Correct! Wrong!

Technician A says that a frozen, plugged, or crimped discharged line from the air compressor and before the air dryer may cause an air compressor to blow the head gasket. Technician B says that a frozen, plugged or crimped discharged line from the air compressor and before the air dryer may cause the compressor to make a knocking sound. Who is correct?

Technician A

Technician B

Both A and B

Neither A nor B

Correct! Wrong!

You are performing an air timing balance test on a combination vehicle. Technician A uses an accurate watch as part of the required equipment. Technician B says that balanced air timing means each axle receives air at the same time and at the same pressure level as needed by the driver. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

The dual circuit foot valve:

has two separate valves that controls two separate brake systems.

is usually suspended from the cab firewall.

is a push-pull valve mounted on the panel in the cab.

operates in a clockwise manner and releases with a counterclockwise motion.

Correct! Wrong!

What style of air valve would be used on a trailer without spring brakes?

Relay emergency

Relay

Anti-compound

Spring brake relay

Correct! Wrong!

When the tractor park control valve pops out.

the spring brake releases.

air begins to build up in the piggyback.

it will not reopen until the treadle valve is depressed and opened.

air in the spring brake chamber is exhausted.

Correct! Wrong!

A driver communicates a complaint of dragging brakes, Technician A says a leaking diaphragm or seal could cause the problem. Technician B says a broken return spring in the service brake section could be the cause. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

What does the double check valve do?

The double check valve ensures that air is released in only one direction at one time.

If one reservoir loses pressure, the double check valve allows the functioning reservoir to supply air to both circuits.

The double check valve alerts the driver as to which direction the air in a particular line is travelling at a given time.

The double check valve ensures proper levels for governor cut-off pressures.

Correct! Wrong!

On an air brake system, the maximum allowable build up time for a single unit (tractor only) between 50 and 90 PSI is:

30 seconds

1 minute

3 minutes

5 minutes

Correct! Wrong!

Tests of brake applications and stroke length are made at _________ minimum air pressure at the brake chamber.

100 psi

80 psi

50 psi

20 psi

Correct! Wrong!

Technician A says that the park and emergency braking system is a distinct air circuit, separate from the regular service brake system. Technician B says that spring brake chambers use air pressure in the opposite way from the service brake chambers. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

What is brake compounding?

Running the tractor in a bobtail position.

Rapidly releasing the air in the spring brake chamber to allow the brakes to be applied.

Simultaneous application of the service and emergency side of the spring brake chambers.

Correct! Wrong!

Air line gladhand seals are made of:

Rubber

Polyurethane

Plastic

Rubber-covered aluminum

Correct! Wrong!

How many ports does a typical relay valve have for a tandem axle?

Two

Four

Five

Seven

Correct! Wrong!

What does the tractor protection valve do?

It ensures against air leakage in the gladhands.

It provides a means of preserving air pressure in sufficient amount to stop the tractor in event of a trailer breakaway.

It provides a means of holding off the spring brake in case of a spring brake chamber air loss.

It senses that the tractor is running without a trailer and automatically reduces the amount of air pressure that can be applied to the tractor''s drive axle(s).

Correct! Wrong!

A heavy truck brake system is being inspected. Technician A says that the proportioning valve should be inspected every time the brakes are serviced. Technician B uses gauges ahead of and behind the proportioning valve to test its function. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

What is a rule that applies equally to almost all air brake systems?

The first sign of moisture in the line indicates that repair is needed.

Air-operated equipment depends on air pressure in only one direction; movement in the opposite direction requires mechanical means.

Because air systems are a closed system, they do not need filters.

Air lines cannot have more than three 90-degree bends per 5-foot section.

Correct! Wrong!

Why is it very difficult to have the same actuation pressure on all axles of a combination vehicle?

Because there are more valves between the foot valve and the trailer axles than the tractor axles, thus increasing restrictions and lowering those respective pressures.

Because the increased length of the lines to the trailer causes a corresponding pressure drop or increase.

The same actuation pressure is impossible to achieve because both the tractor and trailer air systems are two separate and distinct systems.

Because the treadle valve operates the tractor air system, while the trailer supply valve operates the trailer air system.

Correct! Wrong!

During a brake inspection, a technician tests the air supply system. After doing a complete visual and audible examination, finds only that the air system build-up time is slow. Which one of the following could be the cause?

A clogged compressor inlet filter.

A leak in a brake chamber.

An air leak in the cab suspension.

A restriction in the governor line.

Correct! Wrong!

When testing the operation of the trailer hand control valve, a technician should:

move the handle to several intermediate positions, then fully applied position, while listening for leaks and stability and record the maximum application air pressure.

drain the air system to 0 psi, and then allow pressure to build up again, checking the valve in various positions.

record the maximum brake application air gauge reading of the air pressure first, and then drain the system.

listen for air leakage around the handle, as the handle is moved to the applied position.

Correct! Wrong!

When diagnosing a service brake relay valve, all of the following apply EXCEPT:

the air inlet valve leakage is tested with the service brakes released.

apply a soap solution to the area around the inlet and exhaust valve retaining ring to check exhaust valve leakage.

exhaust valve leakage is tested with the brakes applied.

the control port on the service brake relay valve is connected to the supply port on the brake application valve.

Correct! Wrong!

When considering the proper operation of a tractor service brake relay valve:

air line are connected from the service brake relay valve delivery ports to the rear axle service brake chambers.

when the brakes are released, the inlet valve is open in the service brake relay valve.

when the brakes are released, the exhaust valve is closed in the service brake relay valve.

the service brake relay valve is in a balanced position when the air pressure in the rear brake chambers equal reservoir pressure.

Correct! Wrong!

Technicians are discussing quick-release valves. Technician A says that a bad tractor protection valve will cause wheel lockup on the tractor during a brake application. Technician B says a defective quick-release valve can cause a slow front application pressure buildup and reduce stopping ability. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

Technicians are diagnosing the tractor spring brake control valve. Technician A says if the rear axle reservoir is drained to zero air pressure and the brake application valve is applied, the tractor air brake pressure should be at 120 psi. Technician B says when the tractor parking brakes are applied, the air pressure at the tractor spring brake valve delivery port should drop quickly to zero. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

Technician A says that the trailer air supply valve allows air to enter the trailer brake system when its knob is pushed inward. Technician B says that the knob of the park control (system park) valve must be pulled out before the trailer air supply valve can receive air at the control port. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

Technician A says that pressure below 45 psi in the air brake system will cause the knob of the trailer air supply valve to pop out. Technician B says that the pressure below 45 psi in the trailer air brake system will cause the control valve inside the tractor protection valve to close. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

When testing brake application valve leakage, Technician A says that the brake application pressure should be 90 psi (553.6 Kpa). Technician B says that this test is done every 50,000 miles. Who is right?

A only

B only

Both A and B

Neither A nor B

Correct! Wrong!

When conducting operation and leakage tests on single and double check valves:

with air pressure applied to the inlet side of a single check valve, leakage must not exceed specifications at the outlet side.

with air pressure applied to one of the inlet ports on a double check valve, the air pressure should increase slowly at the outlet port.

with air pressure applied to one inlet port of a double check valve, the test gauge at the opposite inlet port should indicate zero air pressure.

when air pressure is released at one inlet port on a double check valve, the air pressure should decrease slowly at the outlet port.

Correct! Wrong!

What does a bobtail proportioning valve do?

It speeds up the exhaust of air from the air chambers.

It speeds up the application and release of the brakes.

It works with the park control valve to provide tractor protection and control trailer parking brake application.

It reduces the amount of air pressure that can be applied to the tractor drive axle(s).

Correct! Wrong!

Which statement below is correct regarding what the trailer spring brake valve does?

Releases air in the reservoir to apply the service brake.

Allows the buildup of air pressure to allow operation of spring brake system.

Redirects air to the spring brake chambers for initial application.

Releases the trailer parking brakes with supply air pressure above 85 psi.

Correct! Wrong!

A relay valve:

speeds up application

speeds up release

is located close to the axle

all of the above

Correct! Wrong!

A driver complains that all the air brakes on his truck are dragging. Where would you look for the problem?

Dirt or rocks under the heal of the foot pedal

A reading on the air application gauge

A stuck foot valve plunger

All of the above

Correct! Wrong!

The relay emergency have is found on:

trailer axles

tractor drive axles

tractor steering axles

both tractor and trailer axles

Correct! Wrong!

Modulated spring brake systems are used for parking.

True

False

Correct! Wrong!

Blended air is the mixing of primary air and secondary air.

True

False

Correct! Wrong!

Relay valves are located close to the foot valve.

True

False

Correct! Wrong!

On air brake systems, pedal travel rather than pedal pressure regulates the brake application force.

True

False

Correct! Wrong!

Tractor protection valves:

A wig-wag (low air warning device) should operate:

An inversion/spring brake modulating valve must be mounted upside down.

The Canadian Motor Vehicle Safety Standards (CMVSS) schedule 121 states that parking brakes must hold an empty or loaded vehicle on a:

Spring brakes commonly operate the _________________ to keep the vehicle from moving when parked.

Cracking pressure" of relay valves refers to:

Which section of the foot valve is used as the primary section?

The CMVSS section 121 states that a visual low air warning device must be located in the drivers forward field of vision.

What is the style of valve often called a "highway valve"?

On a dual air system, a tractor protection valve uses which of the following?

An ideal air braking system can be defined as:

All of the following could cause excessive leakage in an air brake system (service brakes applied) EXCEPT:

If the load and speed of a unit are both doubled, the effort needed to stop is _________ times.

Where would you expect that a quick-release valve would be mounted?

The dual circuit foot valve:

What style of air valve would be used on a trailer without spring brakes?

When the tractor park control valve pops out.

A driver communicates a complaint of dragging brakes, Technician A says a leaking diaphragm or seal could cause the problem. Technician B says a broken return spring in the service brake section could be the cause. Who is right?

What does the double check valve do?

On an air brake system, the maximum allowable build up time for a single unit (tractor only) between 50 and 90 PSI is:

Tests of brake applications and stroke length are made at _________ minimum air pressure at the brake chamber.

Technician A says that the park and emergency braking system is a distinct air circuit, separate from the regular service brake system. Technician B says that spring brake chambers use air pressure in the opposite way from the service brake chambers. Who is right?

What is brake compounding?

Air line gladhand seals are made of:

How many ports does a typical relay valve have for a tandem axle?

What does the tractor protection valve do?

A heavy truck brake system is being inspected. Technician A says that the proportioning valve should be inspected every time the brakes are serviced. Technician B uses gauges ahead of and behind the proportioning valve to test its function. Who is right?

What is a rule that applies equally to almost all air brake systems?

Why is it very difficult to have the same actuation pressure on all axles of a combination vehicle?

During a brake inspection, a technician tests the air supply system. After doing a complete visual and audible examination, finds only that the air system build-up time is slow. Which one of the following could be the cause?

When testing the operation of the trailer hand control valve, a technician should:

When diagnosing a service brake relay valve, all of the following apply EXCEPT:

When considering the proper operation of a tractor service brake relay valve:

When testing brake application valve leakage, Technician A says that the brake application pressure should be 90 psi (553.6 Kpa). Technician B says that this test is done every 50,000 miles. Who is right?

When conducting operation and leakage tests on single and double check valves:

What does a bobtail proportioning valve do?

Which statement below is correct regarding what the trailer spring brake valve does?

A relay valve:

A driver complains that all the air brakes on his truck are dragging. Where would you look for the problem?

The relay emergency have is found on:

Modulated spring brake systems are used for parking.

Blended air is the mixing of primary air and secondary air.

Relay valves are located close to the foot valve.

On air brake systems, pedal travel rather than pedal pressure regulates the brake application force.

Success!

Heavy-Duty Mechanic - Trucks & Equipment