What is a Hydraulic System | How does a Hydraulic Pump Work?

What is a Hydraulic Pump?

A hydraulic pump is an equipment that transforms the mechanical energy of the hydraulic fluid into hydraulic power (hydraulic power such as pressure, flow). This pump produces flow with adequate power to overcome the pressure caused by the load.

The purpose of a hydraulic pump is to flow hydraulic oil by a hydraulic system. It acts as a beating heart of the system. All hydraulic pumps have two major functions:

  • These pumps supply hydraulic flow to other parts (such as hydraulic cylinder, rams, hydraulic motor, etc.) of the hydraulic system.
  • These generate a flow that further produces pressure to overcome the flow resistance.

Hydraulic pump is a type of positive displacement pump that uses for fluid power purposes. It uses to supply hydraulic fluid to different parts of the system like motors, rams, cylinders, etc. In PD pumps, the main purpose of the hydraulic pumps is to supply hydraulic oil to the piston so that the piston can quickly move forward and backward. The power steering pump in a car is an example of hydraulic pumps. Engine transmission oil pumps are another common example.

Moreover, maximum hydraulic pumps are driven by an electric motor and contain a pressure relief valve to prevent the pump from excess pressure.

These pumps mostly use in high flow and low-pressure applications. This is because they force the low-pressure fluids to move at higher speeds and transfer large quantities of fluids in a short time.

What is a Hydraulic System?

A hydraulic system is a transmission technology that uses fluid to transfer energy from an electric motor to an actuator such as a hydraulic cylinder. This fluid is incompressible, and the path of the fluid is as flexible as the wire.

These systems mainly use when high power densities are required or when the demand for loads increases quickly. The hydraulic system is especially applicable for all types of moveable equipment (e.g., excavators) and industrial systems (e.g., presses).

In a wind turbine, the hydraulic system uses to control the slope and the brakes. In some cases, various auxiliary structures (such as cranes and hatches) are also operated with the help of a hydraulic system.

Hydraulic Pump Working

A hydraulic pump works on the basic principle of displacement. A hydraulic pump works in the following steps:

hydraulic pump working

  • A hydraulic pump has two gears that are driver or power and driven or idler gears. These gears mesh into each other.
  • An electric motor uses to supply power to the driver gear through a driving shaft.
  • As the driver gear starts rotating then the driven gear also rotates with its movement.
  • Due to the movement of these gear, a vacuum generates at the inlet section. Due to this vacuum, the pump sucks fluid or oil from a tank or reservoir.
  • The suction and discharge section of the pump have check valves. The main objective of a check is to stop the backward flow of the fluids. This pump sucks fluid from the suction side, and the check valve located at the suction helps to force the fluid inside the pump.
  • As the fluid pressure inside the pump becomes higher than the external fluid pump, the suction valve closes.
  • This fluid needs to pass between the pump gears before discharging because there is no direct way to reach till outlet valve.
  • After entering into the pump, the fluid is trapped between the driver and driven gears.
  • This fluid or oil moves with the movement of the gears. As the fluid flows between the gears, its volume decreases, and the flow rate increases.
  • After reaching on desired flow rate, this hydraulic oil or fluid discharges through the discharge valve and supplies to different parts of the system such as piston or cylinder.

Components of a Hydraulic System 

In maximum cases, hydraulic pumps use to energize the fluids from lower pressure to higher. A hydraulic system has multiple moving and static components. The major components of a hydraulic system are given below:

Hydraulic System Components

1) Casing

This is the external component of the hydraulic pump to ensure the safety of the internal parts. Smaller pumps utilize aluminum casing, while other pumps utilize cast iron castings. The main object of the casing is to stop the splashing of fluid outside the pump. This component also prevents the hydraulic system from any damage if the heavyweight falls on the system’s body.

2) Runner Vanes

A runner is a rotary part of the pump that rotates inside the casing of the hydraulic pump. It has multiple vanes that rotate with the rotation of the runner. With the rotation of the runner vanes, the fluid inside the pump also rotates. This process increases the pressure of the fluid. In addition, these vanes also play a vital function in cooling and lubricating the system.

3) Shaft

The shaft of the pump uses to assemble the runner. This shaft is made of stainless steel or steel. Its size adjusts according to the runner.

4) Bearings

The bearings play an important for the rotation of the runner. Therefore, this is a very important component of the hydraulic system and pump.

5) Sealing

Sealing is an element that prevents the leakage of fluid from the pump. Most pumps fail due to damage to bearing components. A seal can significantly reduce the risk of failure by protecting bearing components from coolants and contaminants.

 6) Oil storage tank

The oil tank has non-compressible fluids (such as hydraulic oil). This tank also prevents the hydraulic oil from contaminants. In this way, the storage tank helps the hydraulic system to work properly.

7) Pipeline

The installation of the pipeline inside the system is simple, but the most important thing is that this pipeline transports hydraulic fluid from one place in the system to another.

8) Electric Motor

An electric motor uses to drive the driving shaft of the system. This driving shaft further drives the driver gear. In this way, an electric motor uses to empower the pump.

9)  Hydraulic drive

A hydraulic actuator is a component that converts the hydraulic power of a fluid into mechanical power to achieve the desired effect.

The actuator looks like this:

  • The hydraulic cylinder generates a linear movement (linear movement).
  • The hydraulic motor generates torque (torque) and rotates.

10) Relief valve

This valve uses to control the pressure inside the system. These valves also have multiple types. A pressure relief valve sends back the excess of fluid’s pressure toward the inlet. 

Types of Hydraulic Pump

The hydraulic pumps have the following major types:

  1. Rotary Vane pump
  2. External Gear Pump
  3. Lobe Pump
  4. Screw Gear Pump
  5. Vane Pumps
  6. Internal Gear Pump
  7. Piston pumps

  8. Axial Piston Pumps 

  9. Radial Piston Pump

  10. Clutch Hydraulic Pump

  11. PTO Hydraulic Pump

1) Rotary Vane pump

This is a positive displacement pump with a series of vanes attached to an impeller that revolves according to the impeller rotation. Sometimes, these vanes can be of different lengths and/or tension to sustain contact with the wall when the pump drives.

rotary vane pumps

An important factor in the design of vane pumps is how the vane is brought into contact with the casing and how the vane tip is treated at this point. There are different designs of the “lip” used for the rotary vane pump. But the primary purpose of the “lip” is to deliver a tight sealing between the inside of the vane and pump casing and minimize wear & tear and metal-to-metal contact.


  • These pumps have good wear characteristics of the vanes
  • Variable-capacity of the pump can be designed by changing the angle of the impeller
  • It delivers a stable flow of hydraulic fluid

2) External Gear Pump

Main article: Different types of Gear Pump

An external gear pump has two gears (driven and driver gears). This pump produces the flow of fluid by passing fluid between these two gears. These gears mesh with each other. One gear (driver gear) drives by a driving shaft. Due to the movement of this gear, the idler (driven) gear also starts rotating. The cavity formed between the teeth of these gears is closed by the pump casing and the side plates (also known as wear plates or pressure plates).

When the gear teeth un-mesh, a limited vacuum generates at the inlet of the pump. After un-meshing, the fluid starts to move to fill the generated vacuum and is transported out of the pump. When the gears mesh again, the fluid starts to enter again inside the pump.

external gear pump, hydraulic system

An external gear pump has herringbone gears, helical gears, or straight spur gears. Spur gears are very common in different applications, and they have easy cutting. These gears have a low cost compared to herringbone and helical gears. Super gears have high noise than other gears.


  • It is the most famous type of hydraulic pump
  • Gear pump has a very low number of moving components
  • These pumps have an easy maintenance
  • These have relatively low cost
  • Gear pumps can tolerate contaminations
  • These are very efficient

3) Lobe Pump

This type of pump is a rotary external gear pump. A lobe pump uses more than one lobe. These lobes rotate around a parallel shaft inside the housing of the pump to flow fluids. In a gear pump, one gear drives to the other one, while in the case of a lobe pump, both the lobes drive by the corresponding drive gears outside the pump housing chamber.

Lobe Pump, hydraulic pump

These pumps use for applications such as biopharmaceutical manufacturing, beverage & food processing, and hygienic processing industries, etc.


  • A lobe pump can handle pastes, slurries, and solids
  • It provides non-pulsating flow
  • It can operate in a dry condition for a long time

4) Screw Gear Pump

Main article: Screw Pump

It is an axial-flow gear pump. The working of this pump is similar to a rotary screw compressor, but the main difference is of working fluid. The flow through a screw pump takes place axially and in the direction of the driver screw. As the driver screw rotates, the inlet hydraulic fluid or oil surrounding traps between the driver and driven screws.  As the screws revolve along the axis, the fluid forces smoothly from one end to another end.

The fluid supplied by the screw pump does not rotate but moves linearly. The screws work like an endless piston and always move forward. There are no pulsations even at high speeds.

screw Pump

Screw pumps have the following five types that are:

i) Single Screw Pump

With a single screw pump, the screw rotor revolves eccentrically in the internal stator. It has only one screw.

ii) Twin Screw Pump

The twin-screw pump consists of two parallel screws that mesh with one another. These screws rotate in the pump casing and are machined with tight tolerances.

iii) Triple Screw Pump

The triple screw pump has three screws (one driver and two driven screws). The two driven screws mesh with the other one driver screw. These screws rotate in a casing that has been machined to close tolerance.

iv) Four-screw Pump

The working of this hydraulic pump is the same as the twin-screw pump. However, this pump has two rotors, and each rotor has two screws.

v) Five-screw pump

The operation of this pump is the same as the triple screw pump, but it has five screws.

Advantages of screw pumps:

  • The screw pumps need low maintenance than other types of pumps
  • These pumps have self-priming capability
  • These can operate in dry condition
  • A screw pump has a low pulsation
  • It has high reliability
  • They have quiet working
  • They pump the fluids with high speed

5) Vane Pumps

A series of vanes slide into rotor slots in a vane pump that revolves inside the pump casing or ring. This casing may have an eccentric shape with respect to the center of the rotor, or it may have an oval shape. In some constructions, centrifugal force causes the vane to make contact with the casing, and the eccentricity of the casing causes the vanes to move inward and outward of the slot.

During the working, as the space enclosed by the casing, rotor, and vanes increases, a vacuum generates at the pump inlet. After this, the atmospheric pressure forces the hydraulic fluid into this generated vacuum.  When the enclosed space decreases, the hydraulic fluid is pushed to drain through the outlet valve.  

6) Internal Gear Pump

Main article: Internal Gear Pump

These hydraulic pump types have external and internal gears. These pumps have compact and small parts.

internal gear pump, hydraulic system

The internal gear pump has one or two more external gear teeth than the internal gear so that these designs have a lower relative speed between the internal and external gears. E.g., if the inner and outer gears have 8 and 9 teethes, respectively, the inner gear will rotate 9 times, and the outer gear will rotate 8 times. This low relative speed means a low rate of wear.


  • It has one stuffing box
  • The internal gear pump has only two moving components
  • It is perfect for high viscosity fluids
  • It has flexible design

7) Piston Pumps

Main article: Piston Pump

A piston pump is a rotating device that uses the working principle of a reciprocating pump to create a flow of fluid. These pumps generally use when higher working pressure of the fluid is needed. They can survive higher pressure compared to a gear pump with the same displacement. Piston pumps traditionally withstand higher pressures than gear pumps with a comparable displacement. But piston pumps have a high price and complex design compared to gear pumps. Equipment designers and maintenance technicians need to understand this complexity to ensure that the other moving components of the piston pump are functioning properly and meet tighter tolerances and stricter filtration requirements. Piston pumps typically use on a truck-mounted crane but can also use for other applications (e.g., in snow and ice control) that require changes to the system flow without changing the engine speed.

This type of pump has a cylinder and a piston. This piston moves forward and backward in the cylinder of the pump. The movement of this piston pushes the hydraulic oil inside the hydraulic pump. In the 1st stroke, it sucks the fluid from the oil tank and pushes it inside the pump, and in the 2nd stroke, it increases the pressure of the fluid that discharges through the outlet valve.  The swash plate angle determines the stroke length of the piston stroke, and the swash plate angle contacts the sliding end of the piston.


  • This pump can bear high pressure
  • It has closure tolerance
  • Truck-mounted cranes
  • These pumps are available in both fix and variable designs
  • Smash plates remain static
  • It has a self-priming ability
  • It has high efficiency

8) Axial Piston Pumps 

The piston of the axial piston pump rotates in a parallel direction to the centerline of the drive shaft of the piston’s block. Due to this, the movement of the revolving shaft converts into an axial reciprocating movement. Maximum axial piston pumps are multi-piston pumps that use one-way valves or ports to pump fluid from the suction area to the outlet area.

axial piston hydraulic pump

9) Radial Piston Pump

In this pump, the piston is positioned in the radial direction within the cylinder block. These pistons reciprocate perpendicular to the centerline of the shaft. These can also classify depending on the arrangement of the pintle valves or one-way valves. Radial piston pumps are accessible in variable and fixed displacements.

radial piston pump

10) Clutch Hydraulic Pump

The clutch pump is a small positive displacement gear pump that is linked with a belt-driven electromagnetic clutch that is very similar to the air conditioner compressor of the vehicle. It is located on the engine compartment of the truck using a mounting kit to fasten it in place.

Clutch Hydraulic Pump Clutch pumps are often utilized when a transmission output port is missing or inaccessible. Typical uses of these pumps are hay spikes, cranes and aerial bucket trucks, etc. Generally, when the pump output flow exceeds 15 GPM, the engine belt will slip under heavy load, and the clutch pump cannot be used in such conditions.


  • Belt driven
  • A clutch pump is a small displacement pump
  • These pumps can use for hay spikes and wrecker applications
  • It doesn’t need adjustment

11) PTO Hydraulic Pump

It is a gear-type pump that uses for heavy-duty applications. It designs for PTO drive applications on all kinds of tractors. PTO hydraulic pump doesn’t require additional gearing.

It has a high-performance aluminum housing and minimal gear play and an end plate that is made of cast iron. The inner splined shaft runs through and is maintained on both ends by roller bearings.

PTO Hydraulic pump


  • PTO hydraulic pump has a self-adjusting wear plate
  • There are very rare cases of leakage
  • It has the least gear clearance
  • It has a casing that is made of high tensile aluminum
  • This pump doesn’t need any extra gearing

Hydraulic Pump Maintenance

The necessity of hydraulic preventive maintenance can determine with time according to the working conditions of the equipment. If you want to maintain your hydraulic pump then follow the following steps:

  • Inspect the level of oil in the oil tank of the power supply unit.
  • Check the changes in oil temperature.
  • Open your pump and check it for oil contaminations.
  • Inspect it for checking any possible leakage. If there is any leakage, then stop it.
  • Check the pipe clamps and screws and tighten them.
  • Monitor the pressure level on the pressure relief valve
  • Inspect the noise of the hydraulic oil pump and the motor for changes. If the pump is generating loud noise compared to before, this high noise may indicate a problem. Try to contact the technician to identify and fix the problem.
  • Before the inspection, check the valve block for leaks.
  • Keep the surface of oil tanks, components, and pipes clean.
  • Contact the technician to determine if maintenance is needed.
  • Read the manufacturer’s instructions book to check if the manufacturer explained any problem.

Applications of Hydraulic Pump

  • The hydraulic pump uses in automobile industries for different vehicles, such as it uses in the power steering system of the car.
  • Hydraulic pumps use for applications such as mining hardware, dump trucks, graders, ranger service devices, vacuum trucks, farm vehicles, loaders, cranes and excavators, etc.
  • These pumps also use for applications such as slitters, steel plants, foundries, bed jacks, forklifts, blenders, lifts, transports, material dealing with, squeezes, and Infusion shaping machines.

FAQ Section

What are the 4 types of hydraulic pump?

The major four types of the hydraulic pump are:

  1. Rotary Vane pump
  2. Gear Pump
  3. Lobe Pump
  4. Screw Gear Pump

Where are hydraulic pump used?

Hydraulic pumps use for different applications such as loaders, mining hardware, dump trucks, vacuum trucks, graders, farm vehicles, cranes, ranger service devices and excavators etc.

Who invented the Hydraulic System?

Joseph Bramah invented the first hydraulic press in 1975.

Does a hydraulic pump create pressure?

A hydraulic pump generates movement of the fluid but it can’t create pressure.

See More:

1) What are the different types of Pumps?

2) What are the different types of Compressors?

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