Customer Service 0232 479 15 50

Hydraulic Cylinder: Structure and Working Principle

Hydraulic Cylinder: Structure and Working Principle


Hydraulic Cylinder: Structure and Working Principle

What is a Hydraulic Cylinder?

A hydraulic cylinder is an actuator that converts pressurized fluid energy into linear mechanical motion in a hydraulic system. It usually consists of a piston and piston rod moving in a cylindrical body. The pressure created by the application of hydraulic fluid (usually oil) to the system exerts force on the piston surface, and this force makes the piston move linearly. Thanks to this structure, precise transmission and control of high forces becomes possible.

Hydraulic cylinders widely used in mechanical engineering and automation systems; It acts as a power transmission element in many areas such as construction machinery, industrial presses, robotic systems and transport equipment.

Modern special equipment offers a high energy density despite its compact dimensions. This need is met by hydraulic drive systems, which are the most efficient solution to ensure reciprocating movement. The basic element of these systems is the hydraulic cylinder.

Basic Structure of Hydraulic Cylinder

The structure of the hydraulic cylinder contains all the components necessary for the pressurized fluid to create a linear motion. Each of these components is critical to keeping the cylinder running efficiently. The main components can be listed as follows:

  1. Body (Cylinder Head)

The body forms the main structure of the hydraulic cylinder. It is usually made of durable steel and reliably holds fluid pressure, ensuring the proper functioning of all components of the cylinder. The external structure of the cylinder is usually in a cylindrical form, which ensures that fluid pressure is safely maintained inside.

  1. Plunger

The piston is one of the most important components of the hydraulic cylinder. A piston is an element that is propelled by the fluid and moves linearly. The piston is moved by the pressure of the fluid, and this movement produces an outward mechanical work. It is important that the piston fits snugly against the inner surface of the cylinder and seals.

  1. Piston Kolu

The piston rod is the extension that is connected to the piston and allows the movement to be transferred to the outside. The piston rod is connected to a fastener on the outside of the cylinder, which transmits the linear motion of the piston to the corresponding system. The piston rod must be durable and long-lasting.

  1. Rod Kolu (Rod Seal)

The concern arm, located on the part of the piston rod that goes out of the cylinder, is the sealing element that prevents fluid leaks. This element prevents the liquid inside the cylinder from leaking out and increases the efficiency of the system.

  1. Seals

Sealing elements are used to prevent fluid leaks in various areas of the hydraulic cylinder. The surfaces on which the piston moves and the places where the piston rod protrudes are protected by sealing elements. These elements must be resistant to high pressure and must not wear out over time.

A hydraulic cylinder; It consists of body, piston, piston rod (rod) and sealing elements. The piston, moving within the cylinder body, creates two separate working cavities:

  • Piston clearance (a): The volume between the body and the piston.
  • Rod clearance (b): The volume between the body, piston and rod.

The pressurized oil is directed to these gaps and the piston is moved back and forth. Thus, the bar makes the exit or retracement movement.

Working Principle of Hydraulic Cylinder

A hydraulic cylinder is an actuator that works by converting pressurized fluid energy into a linear mechanical motion. This principle  is based on Pascal's Principle and explains the basic operating logic of hydraulic systems. According to Pascal's Principle, the pressure in the liquid is transmitted equally in all directions.

We can explain the principle of operation of the hydraulic cylinder in more detail in the following steps:

  1. Pressurized Fluid Flow

In the hydraulic system, the liquid (usually oil) is brought to high pressure, usually by means of a pump. This fluid is directed into the cylinder through the pipes. The pump sends the fluid at high pressure, causing the piston inside the cylinder to move.

  1. Movement of the Piston

The pressurized fluid is directed towards the piston on the inside of the hydraulic cylinder. This fluid, thanks to the pressure it exerts on the piston, pushes the piston and initiates a linear movement. The direction of movement of the piston depends on which side the fluid is on.

  • If the fluid  is applied to the fixed surface of  the piston (the flat surface of the piston), the piston moves outward.
  • If the fluid  is applied to the back of the piston  (the rear surface of the piston), the piston moves inward.
  1. Direction of Movement and Control

The direction of movement of the hydraulic cylinder is  determined by the control valves used  . These valves decide in which direction the fluid will flow and thus allow the piston to move forward or backward. In addition, the steering valves in the hydraulic system allow to control the speed of the cylinder as well.

  • Double-acting cylinder: The liquid can be applied to both the front surface and the rear surface of the piston. Such cylinders can move both forward and backward.
  • Single-acting cylinder: The fluid is applied only to one side of the piston, the reversing movement is usually provided by a spring or other mechanism.
  1. Pascal's Principle

The pressure in the hydraulic system is evenly distributed throughout the entire fluid according to Pascal's Principle. According to this principle, the pressure exerted in the liquid is transmitted evenly through the liquid to each surface of the piston. Thus, high pressure exerted on a small area produces force on a large surface area. This feature gives hydraulic systems the capacity to generate large forces.

  1. Non-compressing feature of hydraulic cylinder

Fluids used in hydraulic systems generally have incompressible properties. Therefore, a direct and fast transmission of force can be achieved thanks to the fluid flow. This feature gives hydraulic cylinders high precision and reliability.

  1. Oil Return and System Continuity

In the hydraulic system, the pressurized fluid needs to return after use. For the reverse movement of the cylinder, the fluid is directed through the cylinder to a return line. This return creates a continuous cycle in the fluid system and ensures that the cylinder operates efficiently.

 

  • When fluid is introduced into the piston cavity, the rod protrudes forward (straight stroke).
  • When fluid is introduced into the rod cavity, the rod is retracted (reverse stroke).

Classification of Hydraulic Cylinders

  1. According to the direction of operation:
    • Single-acting: The liquid moves in only one direction (with a return spring or weight).
    • Double-acting: The liquid acts in both directions.
  2. According to the structure of the working room:
    • Piston cylinder
    • Diaphragm cylinder
    • Telescopic cylinder
  3. By Number of Miles:
    • Single Shaft
    • Twin Shaft
  4. According to the type of liquid feeding:
    • Over miles
    • Through the sleeve
  5. According to the way of mounting:
    • Flanged, eyed, threaded, welded, etc.

Hydraulic Cylinder Performance Calculations

Force Calculation:

F=A⋅pF=A⋅p

  • F: Force (N)
  • A: Piston active area (m²)
  • p: Applied pressure (Pa)

Cylinder Shaft Speed:

V=QAV=AQ

  • V: Spindle speed (m/s)
  • Q: Flow rate (m³/s)

Detailed calculations are presented in the document, accompanied by figures and formulas. You  can also use our online hydraulic cylinder calculator tool according to your need.

Application Areas

Different designs of hydraulic cylinders vary according to the intended use:

  • Piston rollers: Excavators, garbage trucks, etc.
  • Telescopic rollers: For lifting dump truck bodies.
  • Support rollers: In fastening tasks.
  • Boom extension cylinders: In crane systems, load lifting mechanisms.

Each design must be specifically selected according to the type of installation and application load. Especially in telescopic systems, the change in speed and force must be carefully calculated according to the order of extension.