Hydraulics on heavy vehicles
How hydraulics lift and control ton-heavy loads
Many heavy vehicles can do much more than drive: they tip loads lift cranes operate tail lifts and control tools. Behind most of this power is hydraulics — transferring force through liquid under pressure. For a truck mechanic hydraulics is a technical field found on everything from tipping loads to work machines.
§The basic principle
Hydraulics is based on the fact that liquid cannot be compressed. When a pump pushes oil into a cylinder, the piston moves and does work. Because pressure distributes in a closed liquid, a small force on a small area can give a large force on a large area. That is why a hydraulic system can lift loads weighing many tons.
§Central components
- 01Pump — puts the oil under pressure and drives the system.
- 02Tank/reservoir — stores hydraulic oil and allows air and heat to dissipate.
- 03Valves — control direction, pressure and amount of oil.
- 04Cylinders and motors — convert oil pressure into linear movement or rotation.
- 05Hoses and pipes — carry the oil around under high pressure.
- 06Filter — keeps the oil clean of particles.
§Safety at high pressure
Hydraulic systems work under high pressure and a leak can spray oil with great force. A thin jet of oil can penetrate the skin and cause serious damage even if the hole looks harmless. Therefore never search for a leak with your fingers — use for example a piece of cardboard. Always relieve the pressure and mechanically support lifted parts before working under them; a hydraulic cylinder can sink if a valve or hose fails.
§Troubleshooting on hydraulics
Typical symptoms are slow or jerky movement, lack of power or leakage. The cause could be low oil level, air in the system, worn pump, defective valve or clogged filter. Work systematically: check oil level and condition first, then use gauges and manufacturer's data to pinpoint where in the circuit the pressure drops.