Choosing the right hydraulic pump for your needs

Are you in the market for a new hydraulic pump? Then you might currently feel a little bit overwhelmed right now if you’ve had time to explore the different options available. Between hydraulic pump types, styles, fluids, and all other specifications you need to consider, it can be quite a difficult task. Different applications all have their unique needs, and the better understanding of the design characteristics of the different hydraulic pumps you have, the easier it will be to find the right pump for your needs.

This guide is for you who’s currently struggling with your hydraulic pump purchase. Keep reading and learn more about the different hydraulic pump options available, and when you should choose one over the other.


Hydraulic pump types

Using the principle of fluid displacement, a hydraulic pump converts mechanical energy into hydraulic energy, imparting it onto the gears of the pump. Pumps can use either positive or non-positive displacement methods to generate this energy, which affects the rate of flow:

  • Positive displacement pump: A fixed amount of fluid is trapped where the volume stays constant, and the pressure in the pump does not increase. These types of pumps are generally used on low-pressure applications. They are sometimes referred to as hydrostatic pumps. Most pumps use positive displacement.
  • Non-positive displacement pump: The pump changes the velocity of the fluid as needed to create a continuous flow. This means that the pressure can vary with each cycle. The maximum pressure is much higher in a non-positive pump than a positive pump. Some examples of pumps that follow this design include centrifugal and propeller pumps.


Gear pumps

Gear pumps include two types of configurations: internal and external. In either gear pump configuration, two gears mesh together to carry fluid in between the gear teeth. The drive shaft powers one gear, while the other gear moves by linking up to the other.

The different types of gear pumps to choose from include:

  • Internal gear pumps: The internal gear pump, sometimes referred to as a gerotor pump, has two gears, one smaller than the other – usually with fewer teeth in it. The outer gear has its teeth pointing inwards, and the inner gear has its teeth pointing outwards, to make them mesh for part of the rotation. The liquid moves through the space inside the gears. Internal gear pumps create very little pulsation but lack high-pressure capabilities.
  • External gear pumps: In comparison, in an external gear pump, the liquid moves outside of the two gears, between the pump housing and gear to create a vacuum to pull liquid in from the inlet port. External gear pumps offer both higher speeds and a quieter operation.
  • Axial-flow gear pumps: The axial-flow gear pump, sometimes referred to as a screw pump, uses one, two, or three screws to generate an axial flow. These types of pumps offer a very quiet operation since there is no pulsation or contact between metal parts.


Vane pumps

As the name implies, vane pumps work by using small vanes to move in and out of a central rotor to create chambers that transfer the liquid through an oval- or crescent shaped opening. The vanes are often offset for eccentricity. The vanes extend outward, past the edge of the central rotor, creating chambers when they push against the housing wall, extending with the natural curve of the space. The liquid is then forced through the outlet when space is closed. 

Vane pumps have a relatively complex design compared to other pump models and can follow either fixed or variable displacement. 


Piston pumps

Last but not least, the piston pumps. Piston pumps use rotary power to create the flow, and is typically either an axial or radial types, which can offer either fixed or variable displacement: 

  • Inline axial pumps: Inline axial pumps have pistons arranged in a circular pattern in a cylinder block. They have an angled swashplate on one side, and inlet and outlet pots on the other. When the block rotates, the pistons meet the angle of the swashplate, causing them to move in and out and create space in the chamber. This occurs near the inlet valve, thus creating a vacuum to pull in the liquid, while at the outlet valve, the pistons are forced back in, thus pushing the liquid out. 
  • Radial-piston pumps: Radial-piston pumps are available in several different configurations with changes in piston shapes, variable and fixed displacement choices, and valve types. The most common type of configuration has the pistons placed like wheel spokes around an eccentrically placed cam mounted on the drive shaft. When the shaft rotates, the cam moves with it, causing the pistons to push inward as it passes. Each piston has an inlet and outlet port leading to its chamber, where valves control the intake and release of the fluid.
  • Bent-axis pumps: In this design, two parts of the pump meet at an angle. One side, the drive shaft turns a cylinder block with pistons, while the other has bores that match up to these pistons. As the block rotates, the distance between the pistons and the valving surface changes, thus altering the amount of space in the chamber. On the other side, these chambers bring in liquid as the pistons move out, and force it through the outlet as they push in. The angle of the two parts determines the degree of displacement.


Features to consider when purchasing a hydraulic pump

These are the main feature considerations you need to make when you need to invest in a hydraulic pump:

  1. Hydraulic fluid viscosity
  2. Fluid type
  3. Flow rate
  4. Power curves/Torque ratings
  5. Speed
  6. Max operating pressure
  7. Fixed displacement vs. Variable displacement
  8. Maintenance time and costs


Hydraulic pumps from Bygging-Uddemann

We offer complete units of hydraulic high-pressure oil pumps of various types, including oil lines with fittings. For more detailed information about our units, please click the “READ MORE…” button on each item listed on our hydraulic pump page

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