Heavy Duty Equipment Technician

SCR: diesel exhaust fluid (DEF/urea) injected before catalyst, chemically reduces NOx. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Spring brakes hold vehicle safe if air pressure lost; safer than air-applied only. Safety regulations exist because the consequences of ignoring them are severe — injury, death, or legal liability. Know these requirements the way you know your own name.

Modulation valve: output pressure ~ input signal; smooth brake control without lock-up. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

DEF: 32.5% urea, 67.5% deionized water; injected into exhaust before SCR catalyst. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

DPF traps soot; periodic regeneration heats filter to burn accumulated soot. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Powershift: hydraulic control of clutches allows shifts without interrupting power (used in dozers, loaders). On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Transmission brake (hydraulic spring-applied, released by pressure) prevents creep on grades. Material selection directly affects performance, code compliance, and longevity. Using the wrong type can fail an inspection or create a hazard down the line.

ABS: ECU detects wheel lock, rapidly pulses brakes maintaining traction. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Brake fluid must withstand high temperatures from friction; DOT 3/4 (205°C min wet), DOT 5 (260°C). On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Optimal fluid temp: 50-55°C; above 70°C = degradation risk; below 40°C = viscosity issues. Memorize this formula and practise substituting values — exam questions often give you three variables and ask you to solve for the fourth.

Accumulator: gas-charged bladder/piston preload; fluid pressure compresses gas, storing energy. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Cavitation: pump inlet starvation or sudden pressure drop creates bubbles; collapse causes erosion/noise. Troubleshooting is a systematic process: identify symptoms, narrow down causes logically, and verify your diagnosis before replacing parts. This logical approach is what examiners want to see.

Displacement (cc/rev): volume per complete revolution; flow (gpm/L/min) = displacement × RPM. Memorize this formula and practise substituting values — exam questions often give you three variables and ask you to solve for the fourth.

Hydrostatic: pump pressurizes fluid to motor; scalable speed/torque; used in loaders, dozers. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Truck air system: compressor builds 120-140 psi (~8-9 bar); brakes apply at lower pressure. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

ABS/EBS coordinates tractor/trailer to prevent jackknife; proportional braking critical. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

VGT: adjustable vanes change nozzle area, improving low-end torque and high-speed efficiency. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Intercooler: cooler, denser air improves combustion and reduces heat load. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Heavy equipment maintenance: follow OEM intervals but adjust for duty cycle (load/temp). On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Lock: both wheels same speed/torque; improves traction on soft/slippery surfaces. Safety regulations exist because the consequences of ignoring them are severe — injury, death, or legal liability. Know these requirements the way you know your own name.

Load-sensing: pump compensates to load + small margin; reduces waste heat vs. fixed pressure. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Piston rods experience rod-side pressure + external load; buckling is a concern in long rods. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Directional valve spool positions determine which pump port connects to which line (A/B/T). On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Relief valve: as pressure rises, spool opens, spilling excess to tank, protecting system. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Piston pumps: high pressure, high displacement, variable capability; common in mobile equipment. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Gear pumps: simple, robust, fixed displacement, low cost; less efficient than piston pumps. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Common-rail: fuel rail maintains 1000-2000+ bar; injector opens to spray atomized fuel. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Air disc brakes: pneumatic chamber with spring stacks applies friction discs; sealed and durable. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

Waste gate: pneumatic/mechanical valve vents excess exhaust, preventing over-boost. On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.

15W-40: 15W = pumpable at -20°C; 40 = viscosity at 100°C; W = winter grade. Memorize this formula and practise substituting values — exam questions often give you three variables and ask you to solve for the fourth.

Oil analysis: particle count (wear), water%, fuel%, viscosity, TAN, wear metals (Fe, Cu, Al). On the job, a solid grasp of this concept means faster decisions, fewer errors, and work that passes inspection the first time.