ypes of Piston Pumps

Axial Piston Pump (most common in excavators)

Radial Piston Pump (less common)

Axial piston pumps are further classified into:

Swash Plate Type

Bent Axis Type

Most modern excavators use variable displacement axial piston pumps due to their efficiency and ability to adjust flow based on system demand.

3. Key Components

Cylinder Block (Barrel): Houses multiple pistons arranged in a circular pattern.

Pistons: Move in and out to draw in and push out hydraulic fluid.

Swash Plate: Angle controls piston stroke length, affecting fluid displacement.

Valve Plate: Directs the intake and discharge of hydraulic fluid.

Charge Pump: Feeds hydraulic oil to the main pump to prevent cavitation.

4. Working Principle

The engine drives the pump via a coupling.

The swash plate tilts, causing pistons to reciprocate.

During the piston downstroke (suction), hydraulic fluid is drawn into the chamber.

During the upstroke (discharge), fluid is pushed into the hydraulic circuit.

The swash plate angle is controlled to vary the flow output depending on operator commands and system load.

5. Features

Variable Displacement: Adjusts flow to match load requirements, improving fuel efficiency.

Load Sensing: Detects pressure demand and adjusts flow automatically.

High Pressure Rating: Typically operates between 3000–5000 psi (210–350 bar).

Compact and Durable Design: Built for high-performance, continuous operation in harsh environments.

6. Applications in Excavators

Boom lift and lower

Arm extension and retraction

Bucket curl and dump

Swing motor operation

Travel and steering

7. Common Brands

Kawasaki

Rexroth (Bosch Rexroth)

Komatsu

Caterpillar

Doosan / Daewoo

Hydac

8. Maintenance Considerations

Use clean hydraulic fluid to prevent wear.

Monitor pump noise, vibration, and heat.

Regularly check pressure relief settings.

Inspect for internal or external leakage.