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In previous post we have discussed hydraulic oil classifications and hydraulic fluidproperties now we will come to this blog where we will discuss the basic devices those are used in hydraulic system.

Power Supply unit

Basic function of power supply section is to convert the mechanical power from drive motor for providing the required Hydraulic power. The Hydraulic pump is the most important part of power supply unit.

Pump withdraws the hydraulic oil from reservoir and will transmit under pressure to various lines for operating the actuators. We must not the pressure will be produced only if hydraulic oil will find any resistance during flow.

Oil filtration unit

There will be lot of possibilities of introducing impurities with hydraulic oil due to mechanical wear, heating of hydraulic oil and due to various environmental factors. oil filtration unit is also provided with power supply unit for capturing and removing impurities such as dust particles from hydraulic oil. We used to replace the filter after a pre-decided frequency for better efficiency of our hydraulic system

Heat exchangers or oil coolers are also installed with power supply section for conditioning of hydraulic fluid because due to continuous operation , hydraulic oil will be heated and heated oil might damage the seals and may lead the unwanted leakage of hydraulic oil.

So heat exchangers are used with power supply section for cooling the hydraulic oil to keep the hydraulic oil under the desired temperature limit. In case of cold environment , during starting of power unit sometime we need heater also .In power supply unit , we use baffle plates for filtering and separating air or gases and hydraulic oil also cooled through its surfaces.

Hydraulic fluid

Hydraulic fluid is the working medium of hydraulic system that transmits the developed energy from the power supply section to actuators i.e. hydraulic motor or cylinders. There is lot of variations in properties of hydraulic fluid; hence we must select the best hydraulic fluid that meets our system requirement.

We must note that the requirements are not standard but vary from one problem to another problem. Mineral oil based hydraulic fluid are normally preferred for hydraulic system and we called it hydraulic oil.


Valves are used in hydraulic system for controlling the flow of developed energy; valves are used for controlling following parameters in hydraulic system
  1. Direction of fluid flow 
  2. Flow control
  3. Pressure control
  4. Velocity of flow 

Direction control Valve [DC valve]

Direction control valves are used for controlling the direction of movement of actuators by controlling the direction of fluid flow. These types of valves may be operated mechanically, electrically, hydraulically, manually or pneumatically.

Pressure valves 

Such type of valves is used in hydraulic system for regulating and setting of pressure at which hydraulic oil will enter. I have also observed that pressure valves are also used for unloading a pump.

Non return valve

Non return valve, as name indicates, permit the fluid flow only in one direction, I have also observed various types of non return valves such as pilot operated non return valves. 

Pilot operated non return valve may permit the fluid flow in blocked direction also but it will need one pilot pressure as signal.


Cylinders are the main important component of hydraulic system that converts the hydraulic power in to the mechanical power. Hydraulic oil exerts pressure behind the movable piston to generate the movement in piston.

There are basically two types of cylinder 
  1. Single acting cylinder 
  2. Double acting cylinder 

Single acting cylinder 

In case of single acting cylinder , fluid pressure could be applied by one side of piston only hence only drive motion will be possible by hydraulic pressure and for returning stroke there must be any external source such as springs . We may see hydraulic ram for better understanding of single acting cylinder.

Double acting cylinder 

Hydraulic fluid pressure could be applied in both side of piston and hence we may secure forward and reverse stroke by fluid pressure in case of double acting cylinder, we may see synchronous cylinder for better understanding.

Hydraulic motor 

Hydraulic motors are also, like cylinders, actuators that convert hydraulic power in to the mechanical power. Hydraulic motors are used for providing the rotating movement.

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