Hydraulic System: Components, Types & Principles

In this article, I will discuss the components, types and principles of a hydraulic system. Before I go deep into this topic, let me first define for you what a hydraulic system is.


A hydraulic system is a machine in which a liquid is put under pressure by pumps and transmitted to a unit that transforms this pressure energy into mechanical work.


After the transformation of the pressure energy into mechanical work, the liquid return to the pressurizing unit via pipes.


The process repeats itself when the liquid returns to the pressurizing unit.


For you to understand how the hydraulic system works, you have to know the components first.


Components of a hydraulic system.

These are the main components of a hydraulic system;

  1. Electric motor.
  2. Hydraulic pump.
  3. Pressure gauge manometer.
  4. Reservoir.
  5. Valves.
  6. Pipes.
  7. Actuating cylinder.
  8. Accumulator.


1. Electric motor.

The electric motor in the hydraulic system is used to power up the pump for it to pressurize the liquid.


Failure of this electric motor will cause the failure of the entire hydraulic system.


2. Hydraulic pump.

The main function of a hydraulic pump is to pressurize the liquid in the system to move it to the transforming unit.


This is very essential in a hydraulic system because the entire system depends on the pressure provided by the pump.


If the pump cannot work, so is the whole hydraulic system.


3. Pressure gauge manometer.

The pressure gauge manometer is used to read and monitor the pressure values in the hydraulic system so that if it’s too high or low, we can control it.


4. Reservoir.

Reservoir stores liquid used in the hydraulic system. It also receives the returning liquid from the hydraulic system.


5. Valves.

A hydraulic system has several types of valves, each valve has its unique function in the system.


Valves in the hydraulic system are categorized into;

  • Pressure control valve.
  • Directional control valve.
  • Flow control valve.


Pressure control valve: this valve controls the pressure in the hydraulic system. It ensures that there is a balance of pressure in the system, e.g. pressure relief, pressure reducing valve and sequence valve.


Directional control valve: this type of valve determines the path that a liquid follows in the hydraulic system, e.g. check valve, shuttle valve, two-way valve and more.


Flow control valve: this valve is used to control the flow of liquid in the hydraulic system.


6. Pipes.

The main function of the pipes in the hydraulic system is to convey the liquid in certain paths and aid in its circulation.


7. Actuating cylinder.

An actuator is a device that converts the pressure energy of the fluid to mechanical power.


The actuators in a hydraulic system are of three types;

  • Linear hydraulic cylinder.
  • Rotary hydraulic motor (continuous rotation).
  • Semi rotatory actuator (limited-angle movement).


Linear hydraulic cylinder – linear actuators provide a straight motion. They are mostly called rams of jacks.


Without forgetting an important point, linear actuators are further divided into three categories which are;

  • Displacement linear actuator.
  • Single-acting linear actuator.
  • Double-acting linear actuator.


They all convert the pressure energy from the liquid to a linear thrust.


Rotary hydraulic motor (continuous rotation) – it uses a motor shaft to rotate by fluid being forced into the driving members. The common term used for this type of actuator is ‘rotating actuator’.


Semi rotatory actuator (limited-angle movement) – this actuator also rotates but in limited angle movement. The revolutions are 3600 or less.


8. Accumulator.

An accumulator is a device in a hydraulic system that stores energy.


They are divided into three types namely;

  • Dead load accumulator.
  • Spring-loaded accumulator.
  • Gas-loaded accumulator.


Here are more functions of accumulator in a hydraulic system;

  1. It provides fluid to the system at a higher rate.
  2. It acts as a pulsation damper when the system demands a constant delivery.
  3. An accumulator is a standby power source in the event of pump failure.
  4. It compensates for leakages in the system as the system can’t tolerate any leakages.
  5. Accumulators counterbalance whenever the liquid is displaced into the actuating cylinder to fill the void.



Types of hydraulic systems.

There are two types of hydraulic systems namely;

  • Open centre hydraulic system.
  • Closed-centred hydraulic system.


1. Open centre hydraulic system.

This is the type of hydraulic system that has the flow of liquid in the system, but there is no pressure when the actuating mechanism is idle.


The liquid circulates freely in the system, hence the name ‘open centre hydraulic system’.


In this hydraulic system, an open centre selector valve controls pressure, but it’s limited relief.


2. Closed-centred hydraulic system.

In this system, a pump can rest when the liquid is not required in the actuating cylinder.


This means the flow of liquid can be stopped before it reaches the pump.


The control valve is closed at the centre to prevent the oil from reaching the pump.


In a closed centre hydraulic system, the liquid is under pressure whenever the pump is operating.


The main difference between the open centre and closed centre hydraulic system is that the selector valve/directional control valves in the closed centre system are arranged in parallel and not in series.


Principles of the hydraulic system.

The hydraulic system operates under three principles which are;

  • Hydrostatic.
  • Hydrodynamic.
  • Hydrokinetic.


1. Hydrostatic.

In this principle, force is transmitted through a vertical column of hydraulic fluid.


This is the same principle that is used to design a hydraulic jack, a small force on one end can lift a big load on the end.


Consider a vertical column of hydraulic liquid, the column that the small force is to be supplied is a little wider than the column that is supposed to lift the load.


The moment the force is applied on the wider vertical column of hydraulic liquid, it’s transmitted equally through the whole liquid and acts on the ram in the other column in the upward direction lifting the load.


2. Hydrodynamic.

In this principle, there is a pump that provides the pressure in the fluid, which will make the liquid move around the system.


This is applied in earthmoving equipment.


The principle largely relies on the pump for it to work effectively.


3. Hydrokinetic.

This principle doesn’t depend on a pump or a force applied at a certain end.


The power in this system is generated by the high speed of the liquid.


As it moves faster within the hydraulic system, it generates and transmits its power.


This principle is mostly used in designing fluid equipment or hydraulic coupling.


Thank you so much for reading the article. If you have questions, don’t be shy. Leave your comment in the comment section.


Related articles to check.

  1. Underground Water Reservoir Design Recommendations
  2. Reciprocating Pump: Components, Types, Working Principle & Application
  3. Nuclear Power Plant: Introduction, Components And Working Principle
  4. Factors To Consider When Designing An Air Duct System Supply
  5. Ventilation System: Purpose, Types, Working Principle And Maintenance

Leave a Comment