Construction Plant Fitting cheat sheet

Construction Plant Fitting: Machines, Systems, and Safe Maintenance Practice

• Hydraulic system pressure is set by the relief valve, not the pump: pump displacement sets flow, relief valve setting caps pressure, so a slow-but-strong machine points to flow loss (worn pump, clogged suction strainer, aerated oil) while a weak-but-fast machine points to relief or cylinder seal leakage.

• Hydraulic hose selection rule: working pressure rating must be at least 4x the system's maximum continuous pressure for pulsating plant circuits; burst rating is typically 4x working pressure, so never size hose from burst figures.

• Cylinder force = pressure x piston area (bore area minus rod area on the retract side); a 100 mm bore at 200 bar gives about 157 kN extend, but the retract force is lower because rod area is subtracted.

• Contamination target for plant hydraulics is ISO 4406 cleanliness around 18/16/13 for general circuits and 16/14/11 for servo or proportional controls; water ingress above 0.05% by volume accelerates corrosion and oil breakdown.

• Torque rule for structural and running gear bolts: use the manufacturer's torque table plus thread lubricant condition; a torque wrench only measures applied torque, so bolt preload varies with friction and torque-to-yield bolts must be replaced, not reused.

• Diesel engine no-start diagnosis order: confirm cranking speed and battery voltage (above 9.6 V during crank on 12 V systems), then fuel supply and air in lines, then compression and timing; do not chase electrical faults before confirming fuel delivery at the injectors.

• Cooling system: a 50/50 glycol mix raises boiling point and lowers freeze point; pressure caps raise boiling point about 3 degrees C per 0.1 bar, so a failed cap causes overheating under load while the gauge reads normal at idle.

• Outrigger and stability rule: rated capacity charts assume firm level ground and full outrigger extension; capacity falls sharply with radius, so never interpolate beyond the chart or rely on tilt/load moment indicators as a substitute for the chart.

• Lockout/tagout before any maintenance on plant: isolate all energy sources including hydraulic accumulators (bleed to zero), gravity-loaded implements (block or lower), and stored spring energy; verify zero energy at the point of work before disassembly.