The Working Principle and Maintenance Points of Excavator Main Pump

The excavator main pump is a hydraulic pump directly driven by the engine. Its core function is to convert the mechanical energy output by the engine (rotational torque and speed) into hydraulic energy (high-pressure oil flow). The high-pressure hydraulic oil it generates is delivered through complex valve groups and control lines to various hydraulic actuators of the excavator (such as hydraulic cylinders and hydraulic motors), thereby driving the boom, arm, bucket, swing, and travel mechanisms to perform operations. In simple terms: the engine provides "rotation," the main pump converts "rotation" into "high-pressure oil flow," and the high-pressure oil flow then drives the "movements."

Almost all main pumps used in modern excavators are variable displacement piston pumps, which are technologically advanced, highly efficient, and offer strong controllability. They are mainly divided into swash plate type axial piston pumps and bent axis type axial piston pumps.

The working principle of the swash plate type axial piston pump involves multiple piston cylinders evenly distributed around a circumference. The drive shaft rotates the cylinder block, while the ends of the pistons remain in close contact with an adjustable-angle swash plate. When the cylinder block rotates, the angle of the swash plate causes the pistons to reciprocate within their cylinder bores, completing the oil suction and discharge processes. By changing the tilt angle of the swash plate, the pump's displacement can be continuously and steplessly adjusted. A larger angle results in a longer piston stroke, increasing the oil discharged per revolution, as well as the output flow and power. When the angle is zero, no oil is discharged. This forms the basis for energy-saving technologies such as "negative flow control" or "positive flow control."

The working principle of the bent axis type axial piston pump involves a certain angle (oblique angle) between the axis of the drive shaft and the axis of the cylinder block. The pistons are connected to the drive plate via connecting rods. When the drive shaft rotates, it drives the cylinder block to rotate through the connecting rods while forcing the pistons to reciprocate within the cylinders. This design offers better structural rigidity, allowing it to withstand higher pressures and shocks, and typically provides a longer service life. However, it requires higher machining precision and is relatively more expensive.

Modern excavators are typically equipped with 2–3 such main pumps:

Dual-pump system: The most common configuration. One main pump supplies oil to the excavator's boom, arm, and swing functions, while the other supplies oil to the bucket and travel functions. The two pumps can operate independently or combine their flow (when performing a single heavy-duty action, such as lifting the boom) to provide greater force and speed.

Triple-pump system: Used in large or high-end excavators, this system typically dedicates a separate pump to drive the swing system independently, making compound actions (such as swinging while lifting the boom) smoother and more powerful.

There are some important maintenance points for the excavator main pump:

High-quality hydraulic oil of the specified grade must be used, and the oil and filters must be changed strictly on schedule.

When replacing filters or performing any hydraulic system maintenance, extreme cleanliness must be ensured to prevent contaminants from entering the system.

After starting the engine, allow it to idle for several minutes to enable the main pump to fully draw oil before beginning operations. Avoid prolonged operation under extreme pressure conditions.

Regularly check to ensure the oil temperature remains within the normal range and the oil level is sufficient.

If a main pump malfunction is suspected, it should be inspected and repaired by professional technicians using specialized tools. Unauthorized disassembly can easily cause irreversible damage.

Elephant Fluid Power company boasts over a decade of manufacturing experience and is now the largest producer of hydraulic products in Northern China. We operate three specialized production lines equipped with advanced German manufacturing equipment. If you are interested in our products, please feel free to contact us for purchasing inquiries.

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