Hydraulic cylinders - types, design, and applications

Hydraulic cylinders are a key component in many fields of industry, mechanics, and engineering, enabling the precise and efficient transmission of force using a working fluid, most commonly hydraulic oil.

Their applications are extremely diverse, ranging from simple mechanisms to advanced machine systems where high force, precise motion, or both are required. Thanks to the variety of designs and operating principles, hydraulic cylinders can be adapted to specific needs and operating conditions, making them indispensable in many industrial, construction, agricultural, and other sectors. Advances in hydraulic technology contribute to the continuous improvement of these devices, increasing their efficiency, reliability, and cost-effectiveness.

What are the types of hydraulic cylinders?

Hydraulic cylinders can be divided into several main categories, which differ in design and operating characteristics.

• Single-acting cylinders—these are cylinders in which hydraulic fluid is forced into one chamber, causing the piston to move in one direction. The piston returns to its initial position via a spring or under the influence of an external load.
• Double-acting cylinders—in these cylinders, hydraulic fluid can be alternately forced into both sides of the piston, allowing control of the piston’s movement in both directions. They may have a single-sided or double-sided bearing.
• Telescopic cylinders—these feature a piston that allows for an extended working stroke. They consist of several sections that extend one after another, increasing the cylinder’s operating range.
• Tandem cylinders—these are cylinders that are twice as powerful for the same piston diameter. They consist of two cylinders placed one behind the other, which increases the operating force.
• Double cylinders – have two pistons operating independently or synchronously, which allows for greater force or precision of movement.
• Rotary actuators—differ from the others in that they generate rotary motion instead of linear motion. Their design can be vane, screw, or rack-and-pinion.
• Plunger cylinders—in these cylinders, the piston, called a plunger, moves inside the cylinder without the need for a piston rod.

It is worth noting that the selection of the appropriate type of hydraulic cylinder depends on the specific requirements of the application in which it is to be used, including the direction and type of motion required by the machine or device.

Construction of a hydraulic cylinder

A hydraulic cylinder, also known as a hydraulic actuator, is an actuator that converts the energy of fluid pressure, typically hydraulic oil, into mechanical energy, enabling the movement of various structures or machines. The construction of a hydraulic cylinder is relatively simple yet precise to ensure reliability and operational efficiency.

The basic components of a hydraulic cylinder are:

• Cylinders: These are housings that contain the other components of the cylinder and are filled with hydraulic fluid. Cylinders are typically made of steel and are designed to withstand the high pressure of the working fluid.
• Piston: This is a moving component that divides the interior of the cylinder into two chambers. The piston moves along the cylinder under the pressure of the hydraulic fluid. In single-acting cylinders, the piston may be equipped with a return spring that helps it return to its initial position.
• Diaphragm or plunger: In some cylinder designs, a diaphragm or plunger is used instead of a traditional piston; these also move under the influence of fluid pressure.
• Seals: These are components that ensure the cylinder’s tightness and prevent working fluid leakage. Seals are mounted on the piston and at points where other components, such as the piston rod, pass through the cylinder body.
• Piston rod: This is the component that connects the piston to the moving part of the structure or machine to which mechanical energy is transferred. The piston rod is also often responsible for mounting the cylinder to other devices.
• Controls: A cylinder may also include controls that are operated via hydraulic valves. These allow for precise control of the piston’s movement.
• Gland and foot: These are the components that form the front and rear ends of the cylinder. The gland often also serves as a mounting element.

Depending on the type of cylinder, it may have one chamber (in single-acting cylinders) or two chambers (in double-acting cylinders), which allow the piston to move in both directions. All these components are designed to withstand high pressure and ensure long-lasting, trouble-free operation of the hydraulic cylinder.

Applications of Hydraulic Cylinders

Hydraulic cylinders are widely used in many industrial and technical sectors where high force and precision are required. Here are some of their main applications:

• Construction: Hydraulic cylinders are a key component in cranes, where they enable the lifting of heavy booms and other structural elements.
• Mining: In this industry, cylinders are used to operate machines for performing auxiliary tasks.
• Metallurgy: Hydraulic cylinders are used in metallurgical rolling mills that operate under high pressure.
• Industry: They are used in hydraulic presses and in various types of industrial machinery that operate continuously, e.g., in factories, cold storage facilities, and industrial halls.
• Agriculture: Hydraulic cylinders are used in agricultural machinery, such as tractors, combine harvesters, and other harvesting equipment.
• Transportation: In auto repair shops and in the transportation industry, hydraulic cylinders are used to operate various mechanisms, such as in braking systems.
• Woodworking machinery: In this industry, cylinders are used in gluing presses, band saws, and milling machines.
• Opening and closing systems: Hydraulic cylinders assist in opening and closing systems for doors, windows, and gates.
• Earthmoving and road construction machinery: Cylinders are essential in excavators, bulldozers, cranes, and other road construction machinery.

Hydraulic cylinders are valued for their reliability, efficiency, and ability to generate immense force, making them an indispensable tool in many applications. However, because they can be relatively prone to failure, they require constant monitoring of their technical condition as well as periodic maintenance and repairs.

How does a hydraulic cylinder work?

A hydraulic cylinder operates by converting the energy of fluid pressure—most commonly hydraulic oil—into mechanical energy, which enables various structures or machines to move. The operating principle of a hydraulic cylinder is relatively simple and relies on several key components and principles of physics.

The basic components of a hydraulic cylinder are the cylinder (body, housing), the piston, and the piston rod. Hydraulic oil is forced under pressure into the cylinder chamber, causing the pressure to push against the piston, forcing it to extend and thereby moving the piston rod.

In the case of single-acting cylinders, piston movement is possible in only one direction. When fluid is supplied to a single working port, it forces the piston to move in one direction until the end of the stroke is reached. The piston then returns to its starting position, which may be assisted by a return spring or an external force.

Double-acting cylinders do not have a spring and are equipped with two working chambers. Fluid pressure can be applied alternately to both sides of the piston, allowing for control of the piston’s movement in both directions. This enables the piston to move both forward and backward, increasing the cylinder’s functionality.

The operating principle of a hydraulic cylinder is as simple as its design. The energy carrier is a fluid that is forced under pressure into the cylinder chamber, causing the piston to move. In single-acting cylinders, the piston moves toward the base, performing work, while simultaneously compressing the return spring, if present. In double-acting models, the fluid is alternately forced into one side or the other of the piston, allowing the piston to move in both directions.