In hydraulic systems, axial piston pumps are characterized by high efficiency, small size, and high pressure resistance. One of its outstanding features is variable displacement, which allows the pump to adjust the flow output according to system needs. This not only improves energy efficiency, but also ensures precise control of hydraulic actuators.
1. What is hydraulic pump displacement?
Displacement is how much fluid is delivered per shaft rotation of the pump. Displacement in an axial piston pump is calculated through the swash plate angle and the number of plungers involved in the rotation.
Fixed displacement pumps deliver a constant amount of fluid per rotation.
Variable displacement pumps generally modulate the displacement dynamically through external control or load sensing systems.
2. The axial piston pump design
We first have to know its key elements before we can appreciate how the displacement is varied.
Cylinder: Houses some pistons arranged axially.
Pistons: Rotate with the cylinder body, sliding in and out.
Swash plate (bent shaft in some designs): Controls each piston stroke length.
Valve plate: Guides fluid into and out of the piston.
The most significant factor in varying displacement is the angle of the swash plate. If the swash plate is perpendicular to the shaft (i.e., zero angle), no piston stroke and therefore no fluid displacement occurs. As the angle increases in magnitude, the stroke length also increases, and so does the displacement.
3. How a Piston Pump Swash Plate Controls Displacement
In a swash plate axial piston pump, the piston lags the swash plate angle when the shaft rotates. This causes the piston to reciprocate, drawing fluid in and then pushing the fluid out.
Increased swash plate angle = increased piston stroke = increased displacement
This mechanism allows flow to be changed without changing the motor speed – a critical feature in a dynamic system.
4. Methods of Changing Displacement
There are several ways to change the swash plate angle, and therefore the displacement:
a) Manual Control
Manual change pumps with an adjustment lever to change the swash plate angle are provided. These are simple and cost-effective but not automatic.
b) Hydraulic Control (Pressure Compensated)
Swash plate angle in a pressure compensated pump is changed automatically based on system pressure.
If system pressure reaches a predetermined value, the pump reduces the swash plate angle, minimizing flow and saving energy.
This type is ideal for systems with varying demand but constant pressure requirements.
c) Load Sensing Control
Load-sensing variable displacement pumps adjust flow based on actual load requirements.
The control valve senses pressure from the actuator and sends a signal to the pump.
The pump responds by changing the swash plate angle to match the exact flow required.
This improves efficiency and avoids unnecessary heat generation.
d) Electro-hydraulic Control
For advanced applications, the swash plate can be adjusted by an electro-hydraulic actuator, allowing:
Remote control
Proportional regulation
Integration with PLC or computer systems
5. Hydraulic Pumps Bent Axis Pumps and Displacement Control
Not all axial piston pumps use a swash plate. In bent axis designs, displacement is controlled by changing the angle between the drive shaft and the cylinder block.
The principle is the same: the larger the angle, the longer the piston stroke and the greater the displacement.
6. Advantages of Variable Displacement Piston Pumps
Being able to vary displacement has several advantages:
Energy savings: The pump delivers only the required flow.
Reduced heat generation: Reducing excess flow reduces system temperature.
Precise control: Ideal for applications that require frequent changes in speed or force.
Compact system design: No bypass valves or flow restrictors are required.
7. Examples of Hydraulic Piston Pump Applications
Variable displacement axial piston pumps are widely used in:
Construction machinery (excavators, loaders)
Agricultural equipment (tractors, harvesters)
Plastic injection molding machines
Hydraulic presses and test benches
Marine and offshore systems
They are particularly suitable for any system with fluctuating load conditions or where precise actuator control is required.
8. Common models of variable displacement piston pumps available
At Poocca Hydraulic Manufacturers, we offer a full range of variable displacement axial piston pumps, such as:
Rexroth A10VSO / A4VSO / A4VG
Kawasaki K3V / K5V / K7V
Parker PV / PAVC Series
Danfoss 45 / 90 Series Pumps
Yuken A Series
All models support swash plate control and are available with manual, hydraulic or electro-hydraulic adjustment mechanisms.
If your application requires small size, fast response or low noise operation, our variable displacement pumps can meet the requirements of both open and closed loop systems.
The variability in displacement of axial piston pumps is perhaps the most significant cause of their popularity in modern hydraulic systems. Through regulation of the swash plate angle (and, in certain designs, the bent shaft angle), the pump can precisely match system demand in real time.
By way of manual adjustment, pressure compensation, load sensing or electro-hydraulic control, this flexibility brings added energy efficiency, less wear and greater flexibility.
High-performance variable displacement piston pumps for industrial and mobile hydraulic applications worldwide are produced by Poocca Hydraulics manufacturers. For professional advice or purchasing support for axial piston pumps, our professionals are ready at your behest to help you with selection, technical advice and prompt delivery.
Post time: Jul-23-2025
