Hydraulic System Fundamentals
Hydraulic principles including pumps, valves, accumulators, pilot systems, cavitation, and fluid properties.
- Identify hydraulic pump types and variable displacement operation
- Explain relief valve, pressure compensator, and load sensing functions
- Describe pilot systems, accumulators, and pre-charge procedures
- Identify causes of cavitation, aeration, and oil foaming
Lesson 1
Hydraulic Pump Types & Variable Displacement
Pump Types in Heavy Equipment
Heavy equipment uses three main types of hydraulic pumps: gear pumps, vane pumps, and piston pumps. Each has different characteristics for pressure capability, efficiency, and cost.
Gear Pump
Simple, rugged design
Fixed displacement only
Lower pressure capability
Used for: charge pumps, pilot systems
Piston Pump
Most efficient for high pressure
Variable displacement with swashplate
Highest pressure capability
Used for: main hydraulic systems
Variable Displacement
The pump type with variable displacement capability is the piston pump with swashplate. By changing the angle of the swashplate, the pump's output (displacement) can be adjusted from zero to maximum flow without changing engine speed. This allows the system to match flow to demand, reducing energy waste and heat generation.
Load Sensing Systems
A load sensing hydraulic system adjusts pump output based on system demand. A signal line communicates the highest working pressure back to the pump's compensator, which adjusts displacement to maintain a set pressure differential above the load. This provides efficient operation because the pump only produces the flow and pressure needed.
Variable Displacement Advantage
Piston pumps with swashplate can vary output from zero to maximum without changing engine speed. This reduces fuel consumption, heat generation, and component wear.
The piston pump with swashplate provides variable displacement capability. Piston pumps are the most efficient for high-pressure applications. Load sensing adjusts pump output to match system demand.