Hydraulic pumps supply pressurized fluid to the hydraulic motor. Without them, it would be impossible to power many machines used in industry, as well as in many specialized vehicles.
Hydraulic pumps convert the mechanical energy supplied by the drive motor (internal combustion, electric) into hydraulic energy contained in the working medium pumped into the system under the appropriate pressure and performance. This can be done in many ways. Hence the multitude of types of hydraulic pumps – vane, gear, screw and piston pumps. Gear pumps are divided into single-section and multi-section, while piston pumps into single-stream and double-stream pumps. However, regardless of the type, each pump has the same task.
Fixed and variable displacement pumps
Fixed displacement hydraulic pumps are the simplest type of pumps. They have both a simple, uncomplicated structure and a scheme of operation. As a rule, these are gear or vane pumps. Fixed displacement pumps can drive attachment functions in lieu of basic machine functions. It is worth mentioning that they operate with lower pressure.
Variable displacement pumps are mainly piston pumps with a more complex structure than fixed displacement pumps. They are mainly used in working systems and machine drives. They can work under very high pressure. The wide possibility of regulation and control of the oil stream produced determines very good operating parameters. Interestingly, modern variable displacement pumps change their performance on their own, depending on the needs of the hydraulic system.
The variable displacement pump is in turn divided into two sub-types, i.e. closed loop pump and open loop pump. The first of them is most often used in the drive systems of loaders, bulldozers and excavators. In the case of excavators, closed system pumps are also used in the drive of machine rotation. Closed loop pumps are used to move the actuators. They can also power travel hydraulic motors, hydraulic hammers and screens.
Source: “Rodzaje pomp hydraulicznych w maszynach budowlanych” (https://archiwum.e-maszbud.pl)