Getting to know your hydraulic pumps

There are different types of hydraulic pumps that perform different functions. Almost all hydraulic pumps are positive displacement pumps which means that they deliver a precise amount of fluid and can be used in high-power applications of over 10 000psi. Non-positive displacement pumps, such as centrifugal and axial pumps, depend on pressure for the amount of fluid they move. These are more common in pneumatics and low-pressure applications.

What are positive displacement pumps?

These pumps can have either fixed or variable displacement. In fixed displacement the pump provides the same amount of fluid during each pump cycle. Variable displacement sees the pump providing different amounts of fluid based on the speed at which it is run. The physical properties of the pump also place a role in the speed of the fluid.

Different types of pumps

  • Gear pumps are cost effective and more tolerant of fluid contaminates which makes them ideal for rough environments.
    • External gear pumps have two-tight meshed gears within the housing, where the driving gear and other is free-flowing. The fluid is trapped between the gears and rotated through the housing. This fluid is forced through the outlet pump.
    • The design of the internal gear has an inner gear inside an outer rotor gear. The inner gear has fewer teeth and turns the outer gear causing the spacer to go in between them and create a seal. The fluid moves in and through the gears, sealed up and discharged.
  • Vane pumps can be either unbalanced or balanced and have fixed or variable displacement. These pumps are quiet and can work in pressures of under 4000psi.
    • An unbalanced vane pump is a fixed displacement pump with a driven rotor and vanes that slide out in radial slots. As it rotates, the space between vanes increases which creates a vacuum to draw in the fluid. The trapped fluid moves around the system via the rotating vanes and is pushed out as the space between them decreases.
    • A balanced vane pump which is also a fixed displacement pump, moves the rotor through an elliptical cam ring which uses two outlets on each revolution.
    • Variable displacement vane pumps can change via the eccentricity between the rotor and casing. The outer casing ring is also moveable.
  • Piston pumps are perfect for high powered applications.
    • In-line axial piston pumps align the centre of the cylinder block with the centre of the driveshaft. The angle of the swash or cam plate helps to determine the amount of displacement.
    • Bent-axis axial piston pumps lines the centre of the cylinder block at an angle with the centre of the drive shaft.
    • Radial piston pumps use seven or nine radial barrels with a reaction ring, pintle and driveshaft.

For all hydraulic pump needs, Power Team SA can provide professional and expert advice on which pump is best for your machinery needs. With decades of experience supplying quality hydraulic components, Power Team SA is on hand to explain and discuss all your hydraulic needs.