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Axial piston pumps

Axial piston pumps are key components for generating hydraulic pressure and are characterized by the axial movement of pistons within their cylinders. They operate either on the swash plate principle or the bent axis principle. Learn more...

Axial Piston Pumps by Hydromot - A Selection

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In swash plate pumps, the displacement is determined by the angle of a rotating plate, which controls the movement of the pistons.
Bent axis pumps are characterized by the drive shaft and the cylinder block being positioned at an angle to each other, with the pistons connected to the drive flange via ball joints to generate the displacement volume through their motion.

We offer axial piston pumps for both open and closed circuits, tailored to different system requirements.

Open circuit: The hydraulic fluid is drawn from a reservoir and, after passing through the pump and the actuator, is returned to the reservoir. The system pressure depends on the load and may be atmospheric when there is no load. Typical features include suction lines with large diameters and short lengths, as well as the use of flow-dependent directional control valves. These pumps are often used in mobile hydraulics, such as in construction and agricultural machinery, as well as in industrial applications such as machine tools, presses, and wind turbines.

Closed circuit: In this case, the hydraulic oil circulates within a closed system without returning to a reservoir. A separate charge pump or a hydraulic accumulator maintains constant system pressure. Closed circuits offer lower pressure losses, higher efficiency, a more compact design, and more precise control thanks to constant pressure supply. They are primarily used in mobile drive systems.
Many of our axial piston pumps are designed as variable displacement pumps. The adjustment mechanism allows stepless variation of the swash plate or bent-axis angle during operation, enabling the displacement volume and flow rate to be precisely adapted to changing demands. Certain models even allow reversal of rotation by passing through zero displacement. Additionally, we also supply fixed displacement pumps with a constant displacement volume.

Axial piston pumps are known for their high efficiency, which contributes to energy savings, as well as their high power density, which allows significant performance in a compact space. Other advantages include excellent controllability for precise operation and long service life when used properly.

Axial Piston Pumps – Frequently Asked Questions

What is the fundamental difference between an open and a closed circuit in axial piston pumps?

In an open circuit, the hydraulic fluid is drawn from a reservoir, pumped by the axial piston pump to the actuator, and then returned to the reservoir. The system pressure primarily depends on the load and may be atmospheric when there is no load.

In a closed circuit, the fluid circulates continuously between the axial piston pump and the actuator without returning to an open reservoir. A separate charge pump or hydraulic accumulator maintains constant system pressure, enabling more precise performance control.

What specific characteristics distinguish open and closed hydraulic circuits in axial piston pumps?

Open circuits are characterized by large-diameter suction lines, flow-dependent directional control valves, and external filtration and cooling systems. The pump’s capacity is designed for maximum flow output.

In closed circuits, the axial piston pump is part of a compact, self-contained system. Hydraulic filters and hydraulic oil coolers are often installed in bypass configurations, and the pump does not require a separate suction line from a reservoir. These systems are more thermally efficient and compact.

What are the main advantages of a closed circuit compared to an open circuit in axial piston pumps?

Closed circuits offer several key advantages:

Reduced pressure losses: No suction line reduces flow losses
Higher efficiency: Energy is used more effectively
Compact design: No large reservoir is needed
Better controllability: Constant pressure supply enables precise pump control

How does the bent-axis principle work in axial piston pumps, and how does it affect flow rate?

In the bent-axis design, the pistons are mounted in a cylinder block set at an angle to the drive shaft. As the shaft rotates, the pistons move axially, displacing fluid. The flow rate is directly determined by the angle of the bent axis: a larger angle increases displacement, while a smaller angle reduces it.

What role does the adjustment mechanism play in variable displacement axial piston pumps?

The adjustment mechanism allows the swash plate angle to be changed during operation. This makes it possible to adapt the flow rate to current demand, increasing energy efficiency and allowing dynamic control of the hydraulic system.

In which applications are axial piston pumps typically used?

Axial piston pumps are used in many industries due to their high power density and controllability:

Construction machinery (e.g., excavators, loaders)
Agricultural machinery (e.g., tractors, combine harvesters)
Industrial hydraulics (e.g., presses, machine tools)
Wind turbines (e.g., for blade pitch control)
Marine and offshore (e.g., steering drives, winches)

What are the main types of axial piston pumps, and how do they differ?

There are two main types:

Fixed displacement pumps: These pumps have a constant displacement volume and deliver a fixed flow rate at a given speed
Variable displacement pumps: The flow rate can be adjusted via the adjustment mechanism. They allow demand-based performance control and higher energy efficiency. The swash plate design is particularly common

What key advantages do axial piston pumps offer compared to other hydraulic pump types?

Axial piston pumps offer several decisive advantages:

High efficiency: Effective energy transfer
High power density: Compact size with high performance
Excellent controllability: Especially in variable displacement models
Long service life: Robust construction when properly maintained
Versatility: Suitable for open and closed circuits in both stationary and mobile applications

What is the difference between swash plate and bent-axis designs?

Both designs use the axial piston principle but differ in construction:

Swash plate design: The pistons move parallel to the drive shaft and are displaced axially by a tilted plate. This design is widespread and allows compact construction
Bent-axis design: The entire piston assembly is set at an angle to the drive shaft. This design often offers higher power density but is mechanically more complex

What maintenance aspects are especially important for axial piston pumps?

The following maintenance factors are crucial for long service life:

Hydraulic oil quality: Regularly check and replace the hydraulic fluid
Filtration: Keep filter elements clean to ensure optimal oil cleanliness
Operating temperature: Stay within the allowable temperature range
Pressure monitoring: Avoid overloads from pressure spikes
Regular inspection: Check seals, connections, and the adjustment mechanism

How do I choose the right axial piston pump for my application?

Selection is based on several factors:

System type: Open or closed circuit
Displacement volume: Required flow rate in l/min
Operating pressure: Maximum system pressure
Control type: Fixed or variable displacement
Drive power: Available motor capacity
Application environment: Stationary or mobile, temperature range