Cert III Agricultural Mech flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Battery earth lead removal order

Disconnect the negative (earth) terminal first and reconnect it last. This prevents a wrench touching the chassis and completing a short circuit through the positive terminal.

Lockout tagout purpose

Isolates and locks energy sources so machinery cannot start or release stored energy during repair. Applies to electrical, hydraulic, pneumatic and mechanical spring energy.

Torque calculation formula

Torque in newton-metres equals force in newtons multiplied by lever length in metres. A 0.5 m bar with 200 N applied gives 100 N·m of torque.

Vernier caliper resolution

Typical vernier caliper resolution is 0.02 mm. Read the main scale before the zero mark, then add the vernier division that aligns with a main scale line.

Micrometer reading method

Micrometers usually resolve to 0.01 mm. Read the sleeve main scale, then add the thimble value, and apply the zero error correction if the instrument is out.

Four-stroke cycle order

Intake, compression, power and exhaust strokes complete one cycle in two crankshaft revolutions. The camshaft turns once per cycle, at half crankshaft speed.

Diesel compression ignition principle

Diesel engines ignite fuel by heat of compression, typically 16:1 to 22:1. High compression raises air temperature enough to fire injected fuel without a spark plug.

Hydraulic isolation before repair

Release pressure at the accumulator or relief point and cycle controls with the engine off before opening lines. Pressurised fluid can inject through skin and cause serious injury.

Metric bolt grade 8.8 meaning

The first number is tensile strength in hundreds of MPa and the second is yield ratio. Grade 8.8 means 800 MPa tensile and 640 MPa yield strength.

Wheel chocking rule

Chock the wheels that stay on the ground before lifting. This prevents the machine rolling while raised on stands or a jack.

Hearing protection threshold

Hearing protection is required when noise exposure reaches 85 dB(A) over an eight-hour average. Sound doubles in intensity roughly every 3 dB increase.

Specific gravity of charged cell

A fully charged lead-acid cell reads about 1.265 specific gravity and a discharged one near 1.120. Correct readings for electrolyte temperature before judging battery condition.

Two-stroke cycle operation

A two-stroke engine completes intake, compression, power and exhaust in one crankshaft revolution, using crankcase pressure to scavenge the cylinder through transfer ports.

Axle stand use rule

A trolley jack lifts but does not support. Place stands on firm level ground under rated structural points before any part of the body goes under the machine.

Feeler gauge application

Feeler gauges measure small gaps such as valve clearances and spark plug gaps. Combine leaves to match the gap and check that the specified leaf drags slightly.

Coolant concentration check

Refractometer or hydrometer testing confirms antifreeze concentration, commonly 50 percent for freeze and boil protection. Wrong concentration causes corrosion or freezing damage.

Hydraulic pressure force formula

Force equals pressure multiplied by piston area. A 10 MPa pressure on 0.01 m² area produces 100 kN of force, so bore size governs lifting capacity.

Cylinder extend versus retract

Extend force uses full piston area and retract force uses piston area minus rod area. Retract is therefore weaker but faster at the same pump flow.

Hydraulic power calculation

Power in kilowatts equals flow in litres per minute multiplied by pressure in kilopascals, divided by 60000. This estimates the power a hydraulic circuit delivers.

Relief valve function

A relief valve limits maximum system pressure by diverting flow to tank. A stuck-open valve causes weak operation and heat; a stuck-closed valve risks burst lines.

Ohm's law application

Voltage equals current multiplied by resistance. A 12 V circuit drawing 3 A has 4 Ω resistance, useful for locating excessive resistance faults.

Electrical power formula

Power in watts equals voltage multiplied by current. A 24 W lamp on a 12 V system draws 2 A and has about 6 Ω resistance.

Healthy battery resting voltage

A charged 12 V battery rests near 12.6 V after standing. Cranking voltage should stay above about 9.6 V; lower readings suggest a weak or failing battery.

Alternator charging voltage

A working 12 V alternator typically holds 13.8 to 14.5 V across the battery at operating speed. Outside this range, check the regulator and wiring.

Voltage drop testing method

Measure voltage difference across a circuit while it carries load. More than about 0.5 V total drop on a 12 V circuit indicates excessive resistance in cables or connections.

Greasing until relief appears

Pump grease until fresh grease escapes at the seal relief point, then stop. Excess grease can rupture seals and overheat bearings through churning.

Bearing failure main causes

Misalignment, contamination, poor lubrication and over-tightened belts shorten bearing life. Correct alignment and clean lubricant give the longest service interval.

Service interval decision rule

Service when either the hour meter or the calendar interval is reached, whichever comes first. Dusty or heavy-load conditions shorten intervals below the standard schedule.

Filter replacement pairing

Replace air, fuel and oil filters at the scheduled interval and always after contamination events. Change the fluid whenever a filter change indicates debris has circulated.

Seasonal storage preparation

Stabilise or drain fuel, keep the battery on maintenance charge, inflate tyres and protect cylinder rods. This prevents corrosion, flat spots and seal damage.

Hydraulic oil overheating causes

Low oil level, blocked cooler, continuous relief valve bypass or wrong oil grade raise temperature. Excess heat thins oil and accelerates seal and pump wear.

Belt tension check rule

Set belt deflection to the manual specification, usually measured at mid-span. Too loose slips and glazes pulleys; too tight overloads bearings and seals.