Hydraulics in construction and agricultural machinery

Hydraulics is the backbone of most construction and agricultural machinery. It is the hydraulics that lift the excavator bucket, turn the crane arm, control front hydraulics and drive many of the tools you attach to a tractor. As a mechanic you must understand both how the system is constructed and how you work safely with the high pressure.

A hydraulic system transmits force through a fluid typically hydraulic oil. A pump puts the oil under pressure and the pressure is led through hoses and pipes to a cylinder or hydraulic motor which converts the pressure into a movement or a force. The advantage is that you can move very large forces with relatively small components.

• 01Pump: creates flow and builds pressure from engine revolutions.
• 02Tank/reservoir: stores the oil and helps with venting and cooling.
• 03Valves: control direction, pressure and flow to the individual functions.
• 04Cylinder: converts pressure into linear movement (e.g. lifting).
• 05Hydraulic motor: converts pressure to a rotating movement.
• 06Filter: keeps the oil clean so valves and pump don't wear out too quickly.
• 07Hoses, pipes and couplings: carry the oil around the system.

Hydraulic oil lubricates, cools, protects against corrosion and transfers the force. Dirty or wrong oil is one of the most common causes of failure. Keep track of service intervals, use the oil type the manufacturer prescribes and change filter according to specification. When you open a hydraulic system you must work cleanly because even small particles can damage fine valve seats.

• 01Start with a visual inspection: leaks, worn hoses, oil level, and contamination.
• 02Ask the user: when does the error occur, and under what load?
• 03Separate the symptoms: is it lack of force, slow movement, or no function at all?
• 04Use the manufacturer's diagrams and measuring equipment rather than guessing.
• 05Test one thing at a time so you know what changed the situation.

When you work systematically and understand the relationship between pump valves and consumers you can pinpoint the fault faster and avoid replacing expensive parts blindly.