270203 - Hydraulics, Steering, Suspension and Air Brakes

Hydrodynamics in a hydraulic system is best described as:

Transmission of force using confined but stationary liquid Transmission of force or motion through the flow of liquids Transmission of force through a solid lever system Transmission of force using compressed air only

Hydrostatics refers to:

Force transmission using rapidly moving liquid Force transmission using confined liquids that may be stationary Force transmission using compressed gases Force transmission using mechanical linkages only

An example of a primarily hydrostatic application would be a:

Hydraulic motor driving a conveyor Hydraulic steering system using continuous flow through an orbitrol Bottle jack supporting a lifted vehicle with the pump stopped Hydraulic cooling fan that runs at variable speed

Pascal’s law states that pressure applied to a confined fluid:

Is greatest at the pump outlet and lowest at the actuator Acts only in the direction of flow Is transmitted equally in all directions throughout the fluid Is cancelled by gravity at the reservoir

A hydraulic press uses a 2 cm² input piston and a 20 cm² output piston. Ignoring losses, the mechanical advantage in force is approximately:

1:1 2:1 10:1 20:1

To increase mechanical advantage in a basic hydraulic jack without changing pressure, you would:

Decrease the area of the load piston Increase the area of the load piston Increase reservoir size only Decrease oil viscosity only

When storing hydraulic fluid, a key precaution is to:

Store open drums outdoors to allow moisture to vent Leave containers unsealed to equalize pressure Protect fluids from contamination, separation, oxidation and freezing Mix different grades to reduce inventory

A hydraulic system relying on fast oil flow through a motor to create rotation is using:

Mainly hydrostatic principles Mainly hydrodynamic principles Only mechanical principles Pneumatic principles

Which condition is most likely to reduce the effectiveness of a hydraulic system based on Pascal’s law?

Trapped air compressibility in the circuit Use of liquid with higher viscosity Increasing fluid temperature to normal range Using steel instead of aluminum for lines

Some hydraulic reservoirs are slightly pressurized primarily to:

Increase fluid temperature Prevent cavitation at the pump inlet Reduce system pressure Improve electrical grounding

The main contaminants removed by hydraulic filters are:

Water vapour only Solid particles measured in microns Air bubbles only Fuel additives

A filter rated at 10 microns is best described as:

Capable of removing all water from the fluid Capable of removing particles roughly 10 micrometres and larger Only suitable for air systems Too coarse for any hydraulic use

High-pressure hydraulic hose is reinforced with:

Plastic braid only Spiral wire braid or multiple steel wire layers Woven cotton threads Copper tubing strands

Hydraulic tubing size is normally specified by:

Inside diameter only Outside diameter and wall thickness Length only Thread size only

Overheating of hydraulic oil is undesirable mainly because it:

Reduces oil flow in cold conditions Causes oxidation and breakdown of the fluid Improves seal compatibility Increases filtration efficiency

A return-line filter is normally installed:

Between reservoir and pump inlet Between actuator outlet and reservoir Directly in the case drain line only Inside the accumulator shell

A suction strainer in the reservoir is primarily intended to:

Control system pressure Protect the pump from large debris at low pressure Cool the hydraulic oil Vent the system to atmosphere

A hydraulic oil cooler is often placed in the:

Suction line to the pump Return line from the system to the reservoir Case drain line of the pump only Air brake supply line

When replacing a high-pressure hose on mobile equipment, you should also verify:

That the hose has the correct pressure rating and reinforcement type Only that the colour of the hose matches the original That the hose is longer than the original to reduce strain That a smaller inside diameter is used to increase pressure

A clogged hydraulic filter bypass valve opening frequently indicates:

Fluid too cold Filter element is restricted and needs service Relief valve stuck open Accumulator pre-charge too high

Which reservoir design feature helps remove entrained air from hydraulic oil?

Very small surface area Baffles and adequate residence time before oil re-enters the pump suction High-speed stirrer inside the tank Mounting the tank upside down

The primary purpose of any hydraulic pump is to:

Create system pressure directly Create fluid flow that can be converted to pressure by resistance Store hydraulic energy Cool the hydraulic fluid

An axial piston pump with a fixed swashplate angle will:

Provide variable displacement with speed Provide constant displacement per revolution Not move any oil at all Only work in closed-loop hydrostatic drives

A variable-displacement axial piston pump changes flow output by:

Changing oil viscosity Varying the swashplate angle Changing reservoir size Adjusting return line backpressure only

In a system using a fixed-displacement pump and relief valve, system pressure is limited by the:

Pump displacement only Reservoir size Relief valve cracking pressure Hose diameter only

A pressure-compensated variable-displacement pump reduces flow output when:

System pressure reaches the compensator setting Reservoir level drops slightly Fluid temperature is low Filter condition is clean

A directional control valve in a hydraulic system is used to:

Limit maximum pressure Change the path of flow to various actuators Remove contaminants from the fluid Measure pump displacement

A flow control valve is primarily used to:

Change direction of flow Regulate the rate of flow to control actuator speed Vent air from the reservoir Provide emergency stop

When a cylinder reaches the end of its stroke and the pump continues to supply flow, system pressure rises until:

The reservoir vents The relief valve opens The pump stops instantly The oil cooler switches off

A check valve in a hydraulic circuit will:

Allow free flow in one direction and block flow in the opposite direction Relieve pressure at a preset level Mix air into the oil Act as a pressure gauge

If a fixed-displacement gear pump is dead-headed with no relief valve in the circuit, the most likely result is:

Normal operation at lower temperature Rapid rise in pressure and mechanical failure of a component System automatically converts to variable displacement Flow simply stops with no pressure increase

In a load-sensing hydraulic system, the pump output pressure is controlled so that it:

Is always at maximum relief pressure Matches load pressure plus a small margin Is controlled only by engine speed Is unaffected by actuator load

The basic functions of valves in hydraulic circuits are to:

Create mechanical motion Regulate pressure and flow and determine path of flow Cool the oil and store energy Increase engine power

In a single-acting hydraulic cylinder, hydraulic pressure is used to:

Extend and retract the rod Extend the rod only, with gravity or a spring providing retraction Retract the rod only Rotate the rod continuously

A double-acting cylinder differs from a single-acting cylinder because it:

Has no piston seals Uses hydraulic pressure to extend and retract the rod Cannot be used in vertical applications Must be mounted upside down

A hydraulic motor converts:

Electrical energy into heat Hydraulic energy into rotary mechanical energy Mechanical energy into electrical energy Air pressure into hydraulic pressure

Many axial-piston hydraulic motors use what type of swashplate arrangement?

Only variable swashplates Fixed or moveable swashplates depending on design No swashplate at all Chain-driven swashplates only

A hydraulic accumulator can be used to:

Store hydraulic energy in the form of pressurized fluid Replace the pump entirely Vent air from the fuel system Measure oil temperature only

An accumulator also helps the system by:

Increasing pump noise Absorbing pressure spikes and shock loads Eliminating the need for filtration Reducing reservoir size to zero

Common accumulator types include:

Weighted, spring-loaded and gas-charged Pistonless, friction and magnetic Rotary, vane and gerotor Axial, radial and transverse

A gas-charged accumulator typically uses which gas?

Oxygen Nitrogen Carbon monoxide Chlorine

A cylinder with a larger piston area on the cap end than on the rod end will:

Produce greater force on extension than retraction at the same pressure Produce equal force in both directions Produce greater force on retraction Not move under hydraulic pressure

Cushioning at the end of cylinder stroke is used to:

Speed up piston impact at the end of stroke Reduce shock by restricting flow as the piston approaches the end of travel Increase system pressure at all times Replace the need for accumulators

A rod-less hydraulic cylinder is most often used to:

Provide rotary motion Provide linear motion without an external rod projecting from the barrel Store hydraulic energy Filter hydraulic oil

When a hydraulic motor is used in closed-loop hydrostatic drive, it is often paired with:

A pneumatic compressor A variable-displacement pump to control speed and direction A fixed-displacement water pump An electric starter motor

A tell-tale sign of internal leakage in a hydraulic cylinder is:

External oil on the rod surface Load slowly drifting down with no external leaks visible High pump noise at all times Oil temperature dropping below ambient

A weighted accumulator stores energy by:

Using compressed gas Using a heavy weight acting on a piston Using a coil spring only Using a flywheel

During system start-up, a properly pre-charged accumulator can:

Prevent pump from building pressure Allow gradual pressure build-up and reduce shock when valves are shifted Increase flow demand suddenly Eliminate need for relief valves

A spring-loaded accumulator stores energy by:

Compressing a spring as fluid enters the chamber Heating the fluid Cooling the fluid Using centrifugal force only

When servicing an accumulator, a critical safety step is to:

Loosen fittings while system is still pressurized Ensure all hydraulic and gas pressure is safely relieved before disassembly Heat the shell to expand it Store it with maximum pressure inside

A hydraulic motor used as a brake when flow is reversed is acting as a:

Compressor Pump, converting mechanical energy back into hydraulic energy Heat exchanger Filter

A key advantage of hydraulic motors compared with cylinders is:

They cannot stall under load They provide continuous rotary motion suitable for conveyors and drives They require no filtration They do not require hydraulic oil

The primary function of a heavy-duty suspension system is to:

Increase engine horsepower Support the weight of the vehicle and cargo, cushion shocks and maintain axle alignment Reduce tire wear by eliminating axle movement Provide steering assistance only

Longitudinal torque rods in a suspension are primarily used to:

Control vertical axle movement only Stabilize the axle against acceleration and braking forces Support the frame Carry spring load

Transverse rods in heavy-duty suspension systems are used to:

Increase engine torque Improve lateral stability by controlling side-to-side axle movement Increase wheelbase Reduce ride height

An auxiliary spring assembly (helper spring) is designed to:

Provide a softer ride when fully loaded Absorb part of the load when the vehicle occasionally carries heavier loads than normal Replace the main spring entirely Reduce frame height under light load

A key advantage of auxiliary spring assemblies is that they:

Increase load capacity without significantly decreasing unloaded ride quality Eliminate need for shock absorbers Reduce tire contact with the road Remove weight from the frame

Ride height control valves on an air spring suspension system work by:

Manually locking the axle to the frame Maintaining a specified distance between frame and axle by admitting or exhausting air Regulating hydraulic fluid in the shocks Changing differential gear ratio

When supplying a replacement leaf spring for a heavy truck, related parts that should be considered include:

Centre bolt, U-bolts, spring pins, bushings, bolts, nuts and washers Only shock absorbers Only wheel bearings Only air lines and valves

Excessive axle walk or side shift on a heavy truck is most likely caused by:

Loose or worn transverse torque rods or bushings Incorrect tire inflation only High oil pressure Overcharged air conditioning system

On an air spring suspension, a leaking ride-height control linkage connection will likely cause:

Overheated hydraulic fluid Incorrect suspension height and uneven air spring pressures Loss of engine oil pressure Improved fuel economy

A broken centre bolt in a multi-leaf spring pack can lead to:

Improved ride quality Leaf misalignment and axle shift on the spring seat Reduced suspension travel only Increased air pressure in the air springs

When replacing U-bolts on a suspension, best practice is to:

Reuse old U-bolts if threads are clean Install new U-bolts and torque them to the manufacturer’s specification Lubricate the spring leaves with oil Overtighten U-bolts until the spring leaves flatten

Crab steering on mobile equipment allows the machine to:

Turn only in a tight circle Move sideways with minimal forward movement by steering all wheels in the same direction Lock the front axle and steer with the rear axle only Operate without any steering linkage

On a king-pin type steer axle, thrust bearings are located:

Inside the differential case Either above and below the steering knuckle or below the axle to support vertical load Between the wheel studs and nuts Only in the steering gear box

The steering knuckle is connected to the axle beam by the:

Drag link King pin Track bar Shock absorber

The drag link connects which two steering components?

Steering wheel and steering column Steering box pitman arm and left-hand steering arm Steering gear and differential case Idler arm and frame crossmember

The steering axle wheel hub mounts to the spindle using:

Tapered roller bearings and an adjusting/lock nut Plain bushings only Ball bearings only Friction washers only

Excessive free play at the steering wheel on a heavy truck could be caused by:

Improper tire inflation only Worn drag link ends, tie rod ends or steering gear wear Low engine oil pressure Overfilled power steering reservoir

A power steering pump on heavy-duty equipment is usually driven by:

A separate electric motor only Engine accessory drive using belts or gear drive The trailer wheels The air compressor discharge line

If thrust bearings at the top or bottom of a king pin fail, the driver may notice:

Improved steering effort Heavy steering and wander due to improper king pin loading Higher engine RPM Overcharging of the air system

Toe-out on turns in heavy-duty steering geometry is designed to:

Increase steering effort Allow inner and outer wheels to follow correct turning radii Reduce turning radius to zero Eliminate the need for steering stops

A steering axle with worn king pin bushings will most likely show:

Excessive vertical and lateral movement at the steering knuckle Increased air brake pressure Reduced engine oil temperature Improved tire life

After servicing steering linkage components, it is important to:

Increase tire pressure beyond specification Check and adjust front-end alignment as required Remove wheel balancing weights Drain the power steering reservoir

Steering system components such as drag links and tie rods commonly use which type of serviceable joint?

Plain bushings only Ball-and-socket joints with tapered studs Splined couplings only Roller clutches

The coefficient of friction is best described as:

The temperature difference between two surfaces The degree of friction between two surfaces when one moves over the other The pressure in the air tanks The size of the brake chamber

Total stopping distance for a heavy vehicle includes:

Brake lag time only Driver reaction time, brake system lag and actual brake application time Tire wear rate only Engine horsepower rating

The effective size of an air brake chamber is based on its:

External diameter only Effective diaphragm area Spring length Thread size on push rod

Components making up an S-cam foundation brake include:

Brake drum, brake shoes with linings, spider, return springs, S-camshaft, slack adjuster and dust shield Master cylinder and disc rotors only Wedge actuator and caliper only Hydraulic cylinder and drum only

The main purpose of the slack adjuster is to:

Convert rotary motion into linear motion Convert push-rod linear motion into camshaft rotation and provide adjustment for shoe-to-drum clearance Store compressed air Measure lining thickness

Automatic slack adjusters must be:

Adjusted manually every trip Installed correctly and inspected; they self-adjust when brakes are applied through full stroke Greased only once at installation Used only on trailers

A low coefficient of friction between tire and road surface (for example, ice) will:

Shorten stopping distance Increase stopping distance even with properly adjusted brakes Have no effect on stopping distance Increase brake temperature during normal stops

Excessive brake drum diameter from wear or machining will:

Improve braking because of larger surface area Reduce braking effectiveness and may require drum replacement Have no effect on braking Automatically adjust slack adjusters

Heat cracks in brake linings are most likely caused by:

Low air pressure in the tanks Overheating due to excessive or continuous braking Cold ambient temperatures Correctly adjusted brakes

The components that make up the supply circuit on a truck air brake system include:

Only service chambers and rotors Compressor, governor, moisture/contamination control, reservoirs, check valves, safety valves, gauges, tubing and hoses Battery, alternator and starter Slack adjusters and drums only

The primary service brake circuit on a typical tractor supplies air to the:

Steer axle service brakes Drive axle service brakes Trailer service brakes only Parking brake chambers only

A relay valve in an air brake system is used to:

Slow brake application Speed up application and release of the drive axle brakes, reducing lag Store compressed air Act as a foot valve

Spring (park) brakes are applied:

By air pressure only Mechanically by heavy springs when air pressure is released Only by the service foot valve Through hydraulic pressure

The tractor protection valve knob in the cab is usually:

Red and octagonal Yellow and diamond-shaped Blue and round Green and square

The function of the tractor protection valve is to:

Protect the tractor’s air supply if the trailer loses air Increase engine power Control cab temperature Adjust wheel alignment

Moisture and oil in the air brake system are usually controlled by:

Air dryer or reservoirs drained periodically Brake drums only Engine oil filter Power steering pump

A governor in an air brake system is responsible for:

Adjusting slack adjusters Controlling when the compressor loads and unloads Operating ABS valves Regulating tire pressure

A safety (pop-off) valve mounted on the air tank is used to:

Bleed air to prevent over-pressurization Adjust spring brake force Control foundation brake wear Balance the service brake circuits

The trailer supply (emergency) line is used to:

Carry service application air to the trailer chambers Charge and supply the trailer reservoirs Control ABS sensors Vent air from tires

The trailer service line is used to:

Provide air for parking brakes only Carry modulated service air to operate trailer brakes during foot valve application Feed the air dryer Control cab suspension

The trailer air supply valve knob in the cab is usually:

Yellow and diamond-shaped Red and octagonal (stop-sign shaped) Blue and round Green and square

If the trailer supply line ruptures, the tractor protection valve will:

Open and exhaust air from the tractor system Close to protect tractor air supply and cause trailer spring brakes to apply Increase compressor cut-in pressure Disable the foot valve

The order in which axles apply their braking in a multi-axle combination vehicle is influenced mainly by:

Colour of the brake chambers Relay valve locations and cracking pressures in the circuits Tire brand Engine horsepower

An anti-lock brake system (ABS) on a trailer typically includes:

Sensor and tooth wheel, electronic control unit (ECU) and modulator valve Only a mechanical governor Power steering pump and orbitrol Engine control module and injectors

When the trailer ABS system is active during a hard stop, the driver will generally notice:

Complete loss of braking Pulsing of brake application at the wheels to prevent lock-up Constant application of maximum braking force with wheel lock Engine stalling