Rexroth A4VG multi-piston pump and its application in hydraulic systems of construction machinery
The hydraulic pump A4VG is a device from the Rexroth "stable", we have already mentioned the company in another article, and we also presented individual pump models that pass through our repair service. In this text, we will focus the reader's attention on the model designation mentioned in the first sentence. 
Application of the pump in drive systems
This pump is mounted in closed systems, and its most popular application is found in drive systems of construction machinery. It is often referred to as a "drive pump". A prime example of the use of hydrostatic drives in systems responsible for vehicle movement are Liebherr constructions. The manufacturer uses this technology in its loaders and we will take a closer look at these types of construction equipment, as they are most often equipped with the A4VG pump.
The characteristics of this hydraulic pump are presented by the manufacturer as a device perfectly suited for installation in electrified drive systems. A4VG is a variable displacement pump, and it pumps oil based on the movement of pistons in the cylinder (axial multi-piston pump).
How is the performance of a hydraulic pump measured and what is it used for?
An important parameter describing the pump is its performance. The discussed type comes in various sizes, which determine the mentioned descriptive value of the pump. Sizes are captured by the geometric volume expressed in cm3/rev.
A4 variants start from 28 cm3 and end at 250 cm3. This doesn't mean much to a layman, as this value translates into performance presented in l/min. You can easily calculate this yourself using a simplified formula, in which we multiply the geometric volume by the number of revolutions, then divide by a thousand and get the desired number in l/min. Performance expressed in l/min allows to adjust the parameters of the hydraulic motor to our system.
Having this data, we can estimate what size of pump we need to fulfill its role in our machine. Usually, information about maximum revolutions can be found in the technical documentation of the hydraulic pump. With such knowledge, we gain greater awareness of how our equipment works and its capabilities.
Hydrostatic drive in drive systems of loaders
In the previously mentioned loaders, the A4VG pump often serves the entire vehicle's drive system. In Liebherr loaders, the drive system consists of two variable displacement pumps, which pump oil from the tank and transport it through hydraulic lines to two piston motors powering the final drives. This solution includes vehicles belonging to the family of model designations L550 - L580. The efficiency of the machine depends on the performance of the pump at a given moment of its operation.
Closed circuit hydraulic systems are also used in Komatsu loaders, where it is responsible for steering the machine's drive. The Komatsu WA320-8 model powers its drive system with a hydrostatic drive, in which oil is pumped by a variable displacement multi-piston pump. All manufacturers using this type of solution for drive systems emphasize the precision and smoothness in controlling the machine, which also translates into economical engine operation.
The progressing electronization of control systems also does not bypass construction machinery. Both Liebherr and Komatsu use electronic sensors to regulate, for example, the maximum speed in the Komatsu WA320-8 loader is controlled using a programmable speed controller. These examples best illustrate the wide range of applications for the A4VG pump.
Operation and service of hydraulic pumps
Heavy construction equipment is almost constantly exposed to all kinds of damage and breakdowns due to the nature of the tasks performed. Hydraulic systems take on the bulk of the machine's individual functions. The previously mentioned loaders are tasked with lifting and moving material of high density (compacted soil, aggregate). Frequent work cycles and improper equipment maintenance can lead to a malfunction, and even serious damage that immobilizes the vehicle for an extended period.
Noticeable drops in hydraulic drive power, problems with hydraulic fluid leakage, or strange noises that did not occur before, should alert the operator. These may be signs of a hydraulic pump failure and if they are observed, you should contact a professional repair service. Repairing on your own can only worsen the condition of the pump.
At Wibako, we have conducted thousands of repairs of hydraulic pumps and motors of various types of popular brands. We have restored many Rexroth devices to working order, including a large number of A4VG models. We offer repair and service of piston and vane pumps. For those looking for spare parts, we recommend visiting the WIBAKO hydraulics website - entirely dedicated to Bosch Rexroth products.
You can read about how we carry out repairs in the appropriate article, where we present step by step the actions taken by the Wibako workshop on specific cases, both less complicated and more complex. Properly and efficiently conducted repair guarantees a reduction in machine downtime, and thus eliminates unnecessary costs.
