The Hydraulic Pump, 3 Types Explained

Hydraulic pumps are an essential component in hydraulic systems, providing your hydraulic cylinders with the power needed to move and operate your machinery.
The Hydraulic Pump, 3 Types Explained

The Hydraulic Pump, 3 Types Explained

Hydraulic pumps are an essential component in hydraulic systems, providing your hydraulic cylinders with the power needed to move and operate your machinery. The pump converts mechanical energy into hydraulic energy and produces the flow required for the development of actuation pressure. Force generated from hydraulic pumps for the agricultural, mining and earthmoving industries is immense as it must adequately supply pressure required by the hydraulic systems to operate. Determining the type of pump you should use for your machinery requires determining the required pressure for your cylinders, the flow rate of the hydraulic fluid, operational temperatures and the power of the pump. At Kappa Engineering we can assist you in all aspects of hydraulic cylinders. We can give you advice on which hydraulic pump will best suit your system requirements.

How Hydraulic Pumps Work

When a hydraulic pump is in operation, a vacuum is created at the inlet port. This pushes the hydraulic liquid from the reservoir into the inlet line to the pump.  By the action of gears inside the pump, it delivers the hydraulic liquid to the pump outlet port and forces it into the hydraulic system which in turn powers the hydraulic cylinders. These pumps can be either positive-displacement or non-positive-displacement pumps. The latter produces a constant flow of the hydraulic liquid but the output varies because the pressure generated is variable. Positive-displacement hydraulic pumps deliver the same amount of hydraulic liquid on each rotating cycle of the internal pumping gears keeping the flow constant, even if there is a change in pressure.

Types of Hydraulic Pumps

Gear Pumps

Gear pumps are positive-displacement pumps and the simplest type of hydraulic pumps available. They are divided into two categories:

External Gear pumps

External gear pumps have two identical interlocking gears that rotate against each other to produce the flow of the hydraulic liquid. This creates a liquid seal within the pump casing which creates suction at the inlet port of the pump. The hydraulic fluid in the pump is enclosed within the pockets between the gear teeth and the interior housing of the gear pump. The fluid is transferred out of the outlet port into the hydraulic system under pressure. Each gear is supported by a shaft and bearings on both sides, but only one of the gears are driven by a motor. These pumps are commonly used in industrial and mobile hydraulic applications.


  • They run very quietly because of the support of the bearings on both sides of each gear
  • Well suited for high-pressure applications
  • Operate at high speeds
  • No overhung bearing loads


  • Fixed End Clearances
  • Bushings are in a liquid area which causes wear

Internal-gear pumps

Internal-gear pumps work on the same principle as external gear pumps but the two gears are of different sizes with the smaller external gear, the idler, interlocking with the larger internal gear, the rotor. The idler is mounted off-centre to interlock the gear teeth with the rotor gear at one point. The fixed half-moon shaped spacer fills the gap created by the off-centre mounting position of the idler. This shape also causes a seal between the inlet and outlet ports.  The internal-gear pump work cycle consists of three stages:

  1. Filling: As the gears come out of mesh by the inlet port of the pump creating an expanded volume in the fluid. It flows into the gaps created by the gear teeth and it becomes trapped there.
  2. Transfer: The trapped fluid is moved from the inlet port by the rotation of the gear to the discharge port around the casing of the pump.
  3. Delivery: as the gears interlock at the discharge port, the volume of the fluid is reduced and it’s forced out under pressure.


  • The liquid has a smooth and pulseless flow
  • They have marginally more horsepower for the size of the pump


  • They are very expensive
  • They have a limited size range
  • Their pressure ratings are low to moderate
  • Few manufacturers make them

Radial Piston Pump

Radial piston pumps use pistons to pump hydraulic liquid into the hydraulic system. A series of pistons are mounted like spokes in a wheel around a cylinder block with an eccentrical central cam mounted on a drive shaft. The shaft directs the hydraulic fluid. As the drive shaft turns, the cam moves towards the pistons forcing them into the cylinder block. This causes the hydraulic fluid to be sucked into the radially mounted cylinders and then being discharged. As the cam moves away, springs help to retract the piston causing the intake stroke to take place. Check valves are put in place to ensure that hydraulic fluid only enters at the inlet port and only exits at the outlet ports. 


  • They run very quietly(low noise)
  • The pump can handle high loads at low speeds
  • High-pressure levels (up to 1000 bar)
  • High efficiency
  • High reliability

Please watch the following video of a radial piston pump demonstration:

There are many more variations of hydraulic pumps that you can learn about online. To learn more please watch the following video:


It is very important that your machines run as effective as possible with the power needed to execute work effectively. Make sure your hydraulic systems are powered by the right type of hydraulic pump. Speak to the experts at Kappa Engineering if you need any advice regarding hydraulics. Contact us today.

Hydraulic Cylinders for sale from Kappa Engineering

If you need 250 Series hydraulic cylinders, 150 Series cylinders or Tipper Series cylinders, click here to order them from Kappa Engineering. We manufacture hydraulic cylinders with any mounting type or port position you require. We manufacture every component of the cylinder in-house and we design and build custom hydraulics for specialised applications.

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