8 Common Types of Hydraulic Systems in the Fluid Mechanics

Hydraulics involves the use of the physical properties of liquids combined with an application of force. These properties are then applied to scientific fields such as engineering and chemistry to fully utilize the resulting force.

What is a Hydraulic System?

Hydraulic systems are systems that work through transmission. Energy is transmitted through the static force of liquids. Mechanical forces are produced by manipulating the contained fluid using hydraulic cylinders.

Types of Hydraulic Systems

1. Hydraulic Power Pack

Hydraulic power packs are free-standing hydraulic units. They are a source of power that is used to move an actuator such as a cylinder inside a hydraulic system. You will find hydraulic power pack is equipped with various valve connections.

Hydraulic Power Pack
Hydraulic Power Pack


There are different designs of the hydraulic power pack and as such they may differ in features. Some of the features found in the system include;

  • Hydraulic power packs are designed with a variety of valves used to control flow.
  • It is equipped with a filter that sieves any foreign particles out of the fluid.
  • They can be fitted with oil coolers that help maintain the temperature of the system.
  • Pressure-limiting valves are present to prevent system failure due to a build-up of pressure.
  • Sensors are built into the system to help manage the system by analyzing data

Parts of a Hydraulic Power Pack

The system consists of the following parts;

  • Drive motor
  • Hydraulic pump
  • Hydraulic fluid tank
Parts of a Hydraulic Power Pack
Parts of a Hydraulic Power Pack

Working Principle

The independent unit consists of a motor drive, which provides the driving force for the system and is linked to a hydraulic pump using a shaft. The motor drive produces electricity, which is transformed by the hydraulic pump into hydraulic pressure. This pressure is what provides the needed mechanical force.


  • Hydraulic power packs are compact inside making them portable
  • They are not expensive to purchase
  • The power packs have a high power density despite being lightweight.


  • They are prone to overheating and as such require cooling packs to function properly
  • Loss of energy may be experienced during the conversion process
  • It may experience high pressure that may result in failure


There are several applications for this system. They include; plant trailers, cranes, tipping trucks, forklifts, jacks, industrial machinery, pumps, safety harnesses, lifts, and airplanes.

2. Hydraulic Power Unit

Hydraulic power unit is an alternative term used to describe hydraulic power packs. They are independent systems that comprise hydraulic pumps, motor drives, and a fluid tank. It works by converting electrical energy from the drive motor to hydraulic energy using the hydraulic pump.


Hydraulic Power Unit
Hydraulic Power Unit

3. Hydraulic Manifold Block

A hydraulic manifold block is a device that is used to control the fluid. Controlling the fluid by extension controls the pumps or actuators by transferring power through these and other parts. There are two main types of hydraulic manifold blocks; mono-block systems and modular block systems.

Hydraulic Manifold Block
Hydraulic Manifold Block

Parts of the Hydraulic Manifold Block

This system’s main component is a block that has drilled holes. The block is used in conjunction with other parts such as valves and fittings among others to perform its function. These parts include;

  • Small plate
  • Cover plate
  • Valve mounting plates,
  • Valve blocks
  • Header pipe
  • connecting blocks

Working Principle

The hydraulic manifold block consists of integrated hydraulic valves whose connection determines the extent of control one can get. It essentially functions like an electric circuit’s switchboard by giving you the operator the ability to decide the direction of flow as well as the quantity of fluid. The fluid is directed to the selected outlet connected to the device that needs to be powered.


  • The hydraulic manifold has a compact design that makes it suitable for areas with limited space
  • The device is easy to install and simple to operate
  • Using a hydraulic manifold block helps to reduce potential leakage


  • The compact system may be difficult to maintain
  • It may lead to pressure drops in the system
  • Troubleshooting the system is a bit difficult given the centralized design.


The uses of hydraulic manifold bock systems include;

  • Food processing plants
  • Agriculture equipment
  • Off-highway equipment
  • Industrial construction machines
  • Valve operations
  • Oil plants

4. Open Loop Hydraulic System

An open-loop hydraulic system is a linear system where the fluid flows continuously through the system. The pump inlet and actuator-return ports in this system are linked to the reservoir for the hydraulic fluid.

Parts of Open Loop Hydraulic System

  • An actuator
  • Hydraulic pump
  • Hydraulic Fluid tank
  • Valve

Working Principle

In this system, the hydraulic pump is used to move the fluid from the reservoir through the system back to the storage where it draws fresh fluid. Valves for regulating flow and direction are used to control the actuator’s direction and speed.

Open loop Hydraulic Circuit
Open loop Hydraulic Circuit


  • The system is easy to use and maintain.
  • This system is suitable for low-pressure application
  • It is ideal for high-temperature uses as it disperses heat as fluid across the system
  • Open-loop hydraulic systems can be fitted with a variety of valves that help smoothen operations
  • They are cheaper to purchase
  • Contamination is reduced with this type of system
  • They come in multiple designs that can easily be customized to suit your system


  • The design requires a large fluid tank and is therefore not ideal for limited spaces
  • It is more difficult to troubleshoot the open-looped system
  • Can overheat if not equipped with an appropriately sized reservoir


The uses of open loop hydraulic systems use cylinders including agricultural equipment, turbines, construction equipment, and heat exchangers

5. Closed Loop Hydraulic System.

This is a compact system that is typically used for mobile applications. They are also referred to as hydrostatic drives. The fluid in the system does not go back to the reservoir instead it goes from the piston pump and returns to the pump after circulation through the motor.

Parts of the Closed Loop Hydraulic System

  • Piston pump
  • Motor
  • Hydraulic fluid reservoir
  • Control lever
Closed Loop Hydraulic System
Closed Loop Hydraulic System

Working Principle

In a closed-loop hydraulic system, the fluid is pulled from the reservoir using the piston pump. The fluid is then transported to the motor before it is circulated back to the pump. It is fitted with a displacement controller fitted on the swash plate of the pump that you use to control the speed and the direction of the flow of the fluid. Pushing the control lever forward turns the swashplate of the piston pump allowing fluid to get to the motor that begins to operate and pulling it back turns it off.


  • The system is suited for high-pressure applications
  • It helps minimize the usage of fluid as most of it is retained inside
  • Closed-loop systems allow for movement in multiple directions
  • It has a compact design suitable for applications with minimal space
  • The device is lightweight making it the best system for moving devices


  • It is not cost-friendly
  • There is a bigger risk of contamination of the fluid
  • The system functions at a much higher temperature
  • It requires a high-pressure fluid filter


The uses of closed-loop hydraulic systems include; pumps, forklifts, cranes, tractors, oil plants, and refrigerating systems among others.

6. Hydraulic Motors and Cylinders

A hydraulic motor is a rotating rod that consists of a valve, a pump, a reservoir, and a piston. This device is used to convert hydraulic energy to mechanical force in the form of angular displacement and torque that can be used to lift and move objects.

Hydraulic Motor
Hydraulic Motor

Hydraulic cylinders on the other hand are mechanical actuators used to apply pressure to the fluid. This pressure results in linear force and motion, moving the piston. It therefore converts the hydraulic pressure into useable mechanical force.

Hydrauluc Cylinder
Hydraulic Cylinder

7. Aviation Hydraulic System

There can be more than one type of aviation hydraulic system depending on the type of aircraft in question. Aviation hydraulic systems typically comprise the three main hydraulic parts which are the hydraulic pump, fluid reservoir, and motor. These systems are used to power different systems although they are not standard for all crafts.

These systems include wheel brakes flaps and slats, thrust reversers, windshield wipers, flight control surfaces, nose wheel steering, propeller, pitch control, speed brakes, landing gear retraction, loading ramps, and cargo doors.

Aviation Hydraulic System
Aviation Hydraulic System

8. Hydraulic Valve System

This system is comprised of devices that are typically used to control the flow in the system. There are different types of hydraulic valves that execute different roles in the system. Their method of action depends on the design of the device.

Hydraulic Valve System
Hydraulic Valve System

The main categories of valves used in hydraulic systems include;

  • Hydraulic Pressure Control Valves that regulate the pressure in order to maintain it at an optimum level
  • Hydraulic Directional Control Valves that set a course for the flow of fluid mechanically or using pressure
  • Hydraulic Flow Control Valves which control the amount of fluid passing through the system


There are various examples of hydraulic systems that function in different ways. It is key that you understand how they function to decide on which system best suits your needs.

More Resources:

Hydraulic Power Pack – Source: TARGET HYDRAULICS

Hydraulic System and Fluid Selection – Source: MACHINERY & LUBRICATION

Hydraulic Power Unit – Source: TARGET HYDRAULICS

Hydraulics – Source: BRITANNICA

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