Hydraulic Fundamentals

Hydraulics is the transmission of power using:

Compressed air Pressurized liquids, typically oil Electric current Solid linkages only

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

Is reduced at each bend in the piping Acts equally in all directions and at right angles to the containing surfaces Acts only in the direction of pump rotation Cannot be transmitted through hoses

Pressure in a hydraulic system is defined as:

Force multiplied by area Force divided by area Flow multiplied by speed Area divided by flow

The SI unit commonly used for hydraulic pressure is:

Kilowatt (kW) Litre (L) Kilopascal (kPa) or megapascals (MPa) Volt (V)

One bar of pressure is approximately equal to:

10 kPa 100 kPa 1000 kPa 1 MPa

Flow rate in hydraulics is typically measured in:

Kilowatts Litres per minute (L/min) Newtons Joules per second

In a hydraulic cylinder, increasing the piston area while keeping pressure constant will:

Decrease output force Increase output force Have no effect on force Stop cylinder movement

Hydraulic power can be approximated by the formula:

Power = pressure × flow Power = area × distance Power = voltage × resistance Power = flow ÷ pressure

Compared to pneumatics, hydraulics generally:

Operate at lower pressures and lower forces Operate at higher pressures and can produce higher forces Cannot hold loads stationary Use only water as a fluid

A major advantage of hydraulic systems on mobile equipment is:

Inability to overload components High power-to-weight ratio and flexible routing to remote actuators No heat generation No need for maintenance

The primary function of hydraulic fluid is to:

Cool the engine only Transmit power, lubricate components, seal clearances and carry away heat and contaminants Provide electrical insulation Increase exhaust back pressure

Viscosity of a hydraulic fluid is a measure of its:

Colour Resistance to flow (thickness) Electrical conductivity Acidity

If hydraulic oil is too viscous (too thick) at operating temperature, the system will likely:

Leak excessively through clearances Experience high resistance to flow, poor cold start performance and energy loss Operate more efficiently Stop generating heat

Hydraulic oil that is too thin (low viscosity) can:

Improve sealing and lubrication Increase leakage and reduce lubrication film strength Eliminate heat generation Prevent cavitation

Cavitation in a hydraulic pump is best described as:

External leakage from fittings Formation and collapse of vapour bubbles due to low inlet pressure Normal pressure ripple in hoses Filter bypassing due to blockage

A common cause of cavitation at the pump inlet is:

Oversized suction lines Restricted suction line, clogged inlet strainer or low reservoir level Low system pressure at the actuators High ambient temperature only

Hydraulic system contamination can be in the form of:

Only water Solid particles, water, air and chemical degradation products Electrical noise only Fuel vapours only

The most damaging type of contamination for close-tolerance hydraulic components is:

Large visible particles only Small hard particles similar in size to internal clearances Air bubbles Water in large droplets

To reduce contamination, hydraulic system design typically includes:

No filtration to reduce pressure drop Properly sized filters, breathers and clean filling practices Oversized return lines only High engine idle speed

In a simple hydraulic system, the component that converts mechanical energy into hydraulic energy is the:

Hydraulic cylinder Pump Reservoir Relief valve

The component that converts hydraulic energy back into mechanical linear motion is the:

Motor Cylinder Reservoir Filter

Pressure is created in a hydraulic system when:

The pump turns with all valves open to tank Flow from the pump meets resistance to flow at an actuator or restriction Oil returns freely to the reservoir The engine is shut off

The gauge port in a hydraulic system is used to:

Add mechanical leverage Measure pressure at specific locations Lubricate bearings directly Vent exhaust gases

A typical symbol for a fixed-displacement pump includes:

A circle with an arrow through it indicating direction of flow A triangle pointing into a reservoir A square with four ports A zig-zag resistor symbol

Hydraulic system operating temperature that is too high will:

Always improve efficiency Accelerate fluid oxidation, reduce viscosity and shorten component life Eliminate contamination Prevent cavitation

Hydraulic system operating temperature that is too low can:

Reduce viscosity to ideal levels instantly Cause sluggish operation and high pressure drop due to thick oil Eliminate the need for warm-up Improve filtration efficiency only

In the ILM Hydraulic Fundamentals module, parts technicians are expected to:

Design complete hydraulic systems from first principles Understand basic terms, units, laws and relationships used in hydraulic components Perform welding repairs on pressure vessels Adjust engine ECU programming

A double-acting cylinder:

Produces force in one direction only Can produce force in both extension and retraction strokes using pressure on both sides of the piston Has no piston rod Cannot hold a load

If a cylinder with a 50 mm diameter piston is supplied with 10 MPa of pressure, the theoretical extension force (ignoring losses) will:

Increase if piston area increases Decrease if piston area increases Remain unchanged with changes in area Be independent of area

The main difference between laminar and turbulent flow in a hydraulic line is:

Laminar flow is smooth and orderly; turbulent flow is chaotic with energy losses Laminar flow causes more pressure drop Turbulent flow never occurs in hydraulics Laminar flow occurs only in return lines

Flexible hydraulic hoses are used instead of rigid tubing when:

No movement or vibration is present Components move relative to each other or experience vibration Static installations exist only Pressures are extremely low

When air is trapped in a hydraulic system, operation may be:

Smooth and quiet Spongy, erratic and noisy Unaffected Improved due to compressibility

System pressure is normally limited by:

The reservoir size A pressure relief valve or pressure control device Hose length Pump displacement

Hydraulic horsepower can be increased by:

Reducing both pressure and flow Increasing either pressure, flow, or both within component ratings Increasing reservoir size only Changing fluid colour

The primary safety concern when working around pressurized hydraulics is:

Low sound levels Risk of injection injuries, component failure and high-force movement Mild temperatures Exhaust fumes only

Hydraulic fluid cleanliness is often specified using:

Only fluid colour charts International cleanliness codes that define particle counts at various sizes Engine oil viscosity grades only Coolant test strips