What are the Main Hydraulic System Parts – The Ultimate Guide

Simply put, we can define Hydraulic systems as those that use pressurized fluids to carry out their functions. Their principle of operation is that any pressure you apply at any point on the fluid is transmitted without diminishing it.

Examples of Hydraulic System Parts

For your Hydraulic System to properly function, all its components have to work simultaneously. Let us have a detailed look at each of these components and their functions in the system:

Omponents of A Hydraulic System
Components of A Hydraulic System

Hydraulic Pump

This device is responsible for converting the mechanical energy generated by an electric motor into hydraulic energy. This hydraulic energy is what drives the actuator.

There is a reservoir where you fill the hydraulic fluid to be used in your system. The hydraulic pump get sit from there and circulates it all through the hydraulic circuit.

Hydraulic Pump
Hydraulic Pump

The pump operates at a constant speed generated by the motor. We can further classify Hydraulic Pumps into three broader categories:

Reciprocating Pumps

 We mainly use this positive displacement pump where we require a very large displacement pressure. They function more or less like any other four-stroke engine.

A rotating motor motor drives the piston to open and close the valves. This allows the hydraulic fluid to enter and leave the cylinder.

Reciprocating Pump
Reciprocating Pump

This supplies a constant volume of fluid to the entire hydraulic system. The discharge is independent of the pressure at the outlet port of the cylinders.

Centrifugal Pumps

These pumps circulate the hydraulic fluid through rotational kinetic energy. An electric motor generates the rotational energy that powers the impeller pushing the fluid.

Additionally, the centrifugal force displaces the hydraulic fluid to the edges of the pump. The outlet pressure determines the frequency of the fluid delivery.

Entrifugal Pump
Centrifugal Pump

We use these pumps mostly in applications that require a high hydraulic volume flow. Such applications usually require low operational pressure.

Gear Pumps

We can have gear pumps in hydraulic systems working either internally or externally. Both these configurations operate with a similar principle.

They circulate the hydraulic fluid by passing it through the teeth found in their meshing gear set during motion. Remember, they may not be as efficient as the other pumps but they have a high tolerance to fluid contamination.

Gear Pump
Gear Pump

Hydraulic Fluid Reservoir

This is the tank that stores the fluid used in running your hydraulic system. In most cases, this supply is able to compensate for any fluid losses due to evaporations or any form of leakages.

Their design is in such a way that the hydraulic fluid you using can easily expand for easy cooling. The two variations you can find are either a vented reservoir or a pressurized and sealed one.

Hydraulic Fluid Reservoir
Hydraulic Fluid Reservoir

Besides acting as an overflow container for any excess fluid, it also allows for air bubbles in the system to be released. These bubbles are one of the major causes of the failures in your hydraulic system.

Hydraulic Fluid

The major purpose of the hydraulic fluid in your system is to transmit the energy through it. They also serve other purposes such as heat dissipation, lubrication, and regulating contaminants.

You should consider traits like viscosity and seal compatibility when choosing your hydraulic fluid. We can categorize hydraulic fluids into three main classifications namely:

Petroleum/mineral-Based Fluids

This is the most common hydraulic fluid you will find in use currently. Despite having a high quality, you will find them cheaply and readily.

Their properties vary depending on their refining process and the additives included in the final fluid. You might bump into some fluids having a form of dye that lets you identify leaking spots.

Water-Based Hydraulic Fluids

Their composition is mostly water therefore we prefer to use them where fire resistance is required. This means that such systems and their environments can safely operate at elevated temperatures.

Such temperatures may result in the evaporation of water in the fluid raising the viscosity. You will have to add distilled water time and again to counter this shortcoming.

Synthetic Hydraulic Fluids

They are normally man-made in such a way that they can withstand both high pressure and temperature. They have exceptional thermal stability with reduced friction and fire resistance.

However, the downside is that they are toxic to your health and you will need special disposal methods. Additionally, it will cost you more to acquire it compared to other fluids.

Hydraulic Fluid
Hydraulic Fluid


The function of an actuator in a hydraulic system is to convert the hydraulic fluid power into mechanical power. You can regulate the operations of the actuators using the various valves available in the hydraulic systems.

Let us look at the three main types of actuators which we classify based on their motion:

Linear Actuator

This actuator operates in a straight line. The output force and motion are similar to that of a reciprocating motor. We can also refer to them as hydraulic cylinders.

Linear Actuator
Linear Actuator

Rotary Actuator

 Its motion takes a rotational form. This motion produces a torque that actuates the hydraulic system power. We commonly refer to it as a hydraulic motor.

Rotary Actuator
Rotary Actuator

Semi-Rotary Actuator

It functions the same as a rotary actuator but does not complete a rotation.


We use valves in Hydraulic Systems to regulate the fluid pressure and flow rate as well as give it direction. The several ways in which you can actuate these valves include pneumatically, electrically, or mechanically.

Here is a list of some of the valves you are likely to encounter in Hydraulic Systems and their uses:

Pressure-Reducing Valves

They usually operate in a “normally open” position. Normally, they ensure that the reduced hydraulic fluid pressure is maintained at its specific location.

Pressure Reducing Valve
Pressure Reducing Valve

Pressure Relief Valves

We normally use them as a fluid bypass when the system pressure becomes too high. We position them all over the hydraulic system circuit.

Pressure Relief Valve
Pressure Relief Valve

Unloading Valves

They operate at very high speeds with low pressure. In most cases, they work in pairs to move the actuator.

Unloading Valve
Unloading Valve

Counter-balance Valves

They control the rapid acceleration of loads in cylinders. Sudden stoppage of such loads that have weight may damage the cylinders.

Directional Control Valves

It controls the energy distribution in the hydraulic fluid by giving it direction. It can also start and stop the flow of the same liquid through its ports.

Flow Control Valve

As we already know, the motion speed of an actuator relies on the hydraulic fluid flow rate. This valve controls the actuator by governing the hydraulic fluid flow.


These are the components responsible for conducting the hydraulic fluids through the hydraulic system. The physical nature of these pipes determines the efficiency of the hydraulic fluid flow.

Hydraulic Pipelines
Hydraulic Pipelines

We can categorize the pipelines into:

Pressure Pipelines

These pipes carry pressurized hydraulic oil from the reservoir to the actuators.

Return Pipelines:

The pipes carry used hydraulic oil that is under low pressure.


Your hydraulic system is prone to contamination from the normal wear of components and foreign matter. You can use several filter methods to get rid of such contaminants such as such strainers.

The location of filters is usually in the reservoir tank and the pressure and return lines. The reservoir tank also has magnetic plugs that attract and remove any iron or steel fillings in the hydraulic oil.



We can refer to them as hydraulic systems storage batteries. They are able to retain the hydraulic fluid under pressure for use when required.

The stored hydraulic fluid can be used to compensate for any loss of pressure brought about by leakages. In the event that you experience power failure, the accumulator will maintain the hydraulic system pump pressure.


Hydraulic Motors

These motors convert the force from hydraulic fluid pressure into a rotational motion having torque. The hydraulic fluid enters the motor through ports under pressure pushing the motors shaft to create torque.

We can classify hydraulic motors into three based on their design and function:

Gear Motors

They work best in applications having a medium flow rate and pressure.

Vane Motors

Mostly used in hydraulic system applications having a high flow rate with medium pressure.

Radial/Axial Piston Motors

They are best suited for applications having a high pressure and flow rate.

Hydraulic Motor
Hydraulic Motor


The heart of the Hydraulic System is the efficient combination of all these components working efficiently together. If you want to guarantee a safe and efficient operation, carry out proper maintenance of every part.

More Resources:

Hydraulic Calculations – Source: Target Hydraulics

Hydraulic Valves – Source: IQS Directory

Types of Hydraulic Cylinders – Source: Target Hydraulics

Hydraulic System & Fluid Selection – Source: Machinery Lubrication

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