Hydraulic System Components and Their Functions in Detail

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Hydraulic System Components

Every system that transfers energy using pressurized incompressible hydraulic fluids is a hydraulic system. It works on the principle of Pascal’s law. That is, when a pressure is applied to a hydraulic fluid stored in a container, it will be equally distributed in all direction. The hydraulic energy produced as a result of this energy transfer is used for applications like lifting, holding and moving goods.

Transferring fluids directly through a pipeline won’t create any hydraulic pressure. Instead, the system comprises of different hydraulic components like pump, actuators, valve, filter, reservoir, etc… They need to be arranged in a proper fashion to create an efficient hydraulic system.

The aim of this article is to help the readers to identify hydraulic system components and its functions. Details regarding some of the important hydraulic system components and their functions are included in this article.

Hydraulic Reservoir

The lifeblood of every hydraulic system is hydraulic fluid. This fluid required to drive the hydraulic system is stored in a reservoir/tank. The size of the reservoir will vary depending on the hydraulic system and application used for. Air trapped inside the fluid will cause problems like aeration. So, a reservoir is designed in such a way to remove trapped air and to cool the pressurized hydraulic fluid. Also, extra space is provided in the system to avoid overfilling as a result of oil expansion. A rim at the filler neck of most of the reservoir is the maximum limit for filling. Another method to prevent overfilling include checking the fluid level using a glass or plastic sight gage, a tube, or a dipstick.

Vented reservoir and pressurized reservoir are the two categories of the reservoir. The vented reservoir is open to the atmospheric pressure and the air enters and escapes through the vent line of the reservoir.  A filter is integrated on the vent line to remove contamination from the atmosphere. Such reservoirs are placed at the highest point of the hydraulic system to provide maximum gravity/force to the flow. High altitude applications like aircraft use pressurized reservoirs to store hydraulic fluids. The fluid will be closed to the atmosphere and pressurized.


The major concern regarding any hydraulic fluid is contamination. The rust, foreign particles and water are some contaminants that can cause the failure of any hydraulic system. Filters are used in hydraulic systems to remove these foreign particles and to purify the fluid. It is important to clean or replace the filter at regular intervals. Otherwise, the pressure of the hydraulic fluid gets reduced and will result in other issues. Generally, the filter units are installed in pressure and return lines to prevent damage of major components.

According to JIS B 8356: 1993, there are different types of filters. Reservoir filters, line filters, off-line filters are some among them. Also, other cleaning equipments like air breather, magnet separators, oil filling ports, etc.. are available for removing contaminants.

The reservoir filters are placed before the pump to prevent the entry of contaminants into the pump. They are of two types; suction filter and return filter. The suction filters are installed at the pump suction port and the return filter clean the fluid returning to the reservoir after the operation. Line filters are used to remove contaminants from the working fluid. These filters are selected depending on the pressure, flow rate and filtration ratings. Off-line filters purify working hydraulic fluid in the reservoir using a pump and filter. 

Hydraulic Pump

In the hydraulics industry, a pump is considered as the heart of every hydraulic system. Because a pump is a component that converts the mechanical energy of fluids to hydraulic energy. Hand pumps and power driven pumps are the two categories of hydraulic pumps. Power driven pumps are commonly used in the hydraulics industry. Hand pumps are suitable for emergency conditions, where the power pumps fail. Piston pumps, gear pumps and vane pumps are the important classifications of power pumps. Our previous article Hydraulic pumps Types contains details regarding hydraulic power pumps and its applications.

Hydraulic Valve

In a hydraulic system, valves have multiple functions. They direct the flow of fluid through the system, control flow of fluid, and regulates the pressure of fluids. What the valve does to perform all these functions is, just opening and closing. Mechanically operated, electric-solenoid operated and pilot operated valves are available in the market. Pilot operated valves are used in most of the applications of hydraulics.Directional control valve, pressure control valve, and flow control valve are three important types of hydraulics valve.  The directional control valve directs the flow of fluid, pressure control valve will monitor and regulate the pressure of fluids, and the flow control valve controls the fluid flow through the system. The article Types of Hydraulic Valve will provide more details on hydraulic valves.

Hydraulic Actuators

Hydraulic actuators convert hydraulic energy into mechanical energy. Cylinders and motors are the two important type of actuating devices. The hydraulic cylinders produce a unidirectional force. So, they are called linear motion actuators.Types of Hydraulic Cylinder contains more details on hydraulic cylinders. A hydraulic motor is another type of actuating device that converts hydraulic energy into rotating mechanical energy. The flow of fluid towards the motor determines the rotating speed. Gear, vane, and piston are the three classifications of hydraulic motors. Gear and vane motors are simple rotating systems with advantages like low cost and high rpm. The complex piston motors are suitable for high-quality drive systems.


Hydraulic systems use accumulators for energy accumulation, shocks absorption, and absorption of pulsations. Accumulators help to achieve a large flow rate and to minimize the noises and pulsations. Bladder type, diaphragm type, piston type, spring type, and weight loaded type are the different types of accumulators. Weight loaded type accumulator is designed for large-scale machinery and spring type accumulators are used to prevent pulsations.

Hydraulic Seals

Hydraulic seals are usually non-metallic, quite soft rings made out of materials like rubber, PTFE, and polyurethane (AU). Seals prevent leakage of hydraulic fluids. Static and dynamic seals two major classifications of hydraulic seals. Dynamic seals are used between parts having relative motion. Similarly, static seals are used in between parts, that doesn’t require motion. Piston seals, rod seals are examples for dynamic seals.

Hydraulic Hoses

The flexible hydraulic hoses connect separate components like pumps, motors, cylinders, etc.. and transfer fluid between them. The flexible nature of hoses makes it suitable for applications requiring less space. Also, ease of maintenance and installation are other benefits of hydraulic hoses. Since the hydraulic system operates under high temperature and pressure, the hoses are constructed with several layers of reinforcement. Reinforced, coiled, corrugated, articulated and multi-element are different types of hydraulic hoses available.

Tubings and Pipings

Hydraulic tubes and pipes have the same function of hydraulic hose. They transfer fluid between the components of the hydraulic system. A pipe/tube is a tubular section or hollow cylinder that will allow the passage of hydraulic pressure. Due to its rigid nature, such connections require more space and installation time. Both tubes and pipes are interchangeable.

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