Hydraulic Cylinders

Hydraulic cylinders are widely used in engineering vehicles and other mechanical applications. A cylinder is a device that converts fluid power into linear mechanical force and motion. A hydraulic cylinder is a linear actuator used for converting fluid energy to an output force in a linear direction for performing various tasks. Some of the important tasks performed by a hydraulic cylinder are pulling or pushing in engineering applications like in machine tools, earth moving equipments, construction equipments and space applications. The application of hydraulic cylinder can be seen in simple car jacks to complicated robotics as well. Small hydraulic cylinders are widely demanded for they can be easily carried and installed in any system.

Hydraulic Cylinder Design: Components of a Hydraulic Cylinder

The basic structure of a hydraulic cylinder is very simple. It contains three main parts which we are explaining below:

Cylinder body:

Like other cylinders, the hydraulic cylinder is also a round body, referred as cylinder barrel. The cylinder body houses the internal parts of a hydraulic cylinder. All hydraulic cylinder bodies are made of very strong metal because they have to deal with high hydraulic pressure and physical strain. The process of filling the cylinder is same as filling water in a barrel. The hydraulic fluid which is inside the cyclinder produces pressure and pushes against all sides. The hard steel body prevents the hydraulic fluid from escaping.

Hydraulic Piston:

This is another component of hydraulic cylinder. The hydraulic piston is a round component which is fixed inside the cylinder body. The piston is designed in such a way that it fits firmly against the interior sides of the cylinder as the piston moves forward when hydraulic fluid is forced into the cylinder. A powerful hydraulic cylinder is one in which pressure builds up to the highest level with the pushing of the piston. A seal or gasket surrounds the hydraulic piston in applications which need very high pressures. This gasket moves with the piston which produces the high internal pressure needed for maximum hydraulic pushing force.

Hydraulic Rod:

The third component of a hydraulic cylinder is the hydraulic rod which connects the piston to other parts. Made of steel or other metal, this hydraulic rod extends through the top of the cylinder body. When the piston moves, the rod is pushed with strong force. When pressure drops, the piston and the rod return to its starting position. The hydraulic rod can pull or push, depending on the design of the hydraulic cylinder.

Common Applications of Hydraulic Cylinders

• Hydraulic cylinders are used in almost all types of construction equipment like as excavators, bulldozers, back hoes, cranes and graders.
• Hydraulic cylinders are used in elevators in buldings. Hydraulic elevators use large compound telescoping cylinders.
• Hydraulic cylinders are also seen in large trash dumpsters to compact trash.
• In the trasportation and automotive, hydraulic brakes make use of hydraulic cylinders.
• In various industries, hydraulic cylinders are fixed on forklifts and jacks.
• In domestic applications, log splitters use hydraulic cylinder rams to split firewood.
• The hydraulic cylinders are used for all fields of engineering that comprise of earth moving, mining industry, construction machinery, plant engineering, defence technology, automotive engineering, mechanical engineering, textile industries, railways, power plants, agricultural machinery etc.

Hydraulic Cylinder Repair

Check out
A User's Guide to Hydraulic Cylinder Troubleshooting
Repairing Hydraulic Cylinders for Effective Performance

Types of Hydraulic Cylinders

As per their functions, cylinders are classified as:

1. Single acting cylinders

In this type of cylinder, the oil pressure is fed only on one side of the cylinder either during extension or retraction. When the oil pressure is cut-off, these cylinders return to the normal position either by a spring or by an external load.

2. Double acting cylinders

: These are operated by applying oil pressure to the cylinder in both directions. Due to inherent mechanical problems associated with the spring, single acting cylinders with spring return are not used in applications using larger stroke lengths. They may be either single rod ended or double rod ended type.

3. Plunger or ram cylinders

: These are used as a single acting cylinder in a vertical position so that the load on the cylinder can retract when the oil supply is stopped. Eg. Cylinders used as lifts in automobile service stations.

4. Telescoping cylinders

: These cylinders provide long working strokes in a short retracted envelope and are used in mobile applications such as tilting of truck dump bodies and fork lift trucks, hydraulic cranes etc.

5. Cable cylinders

: These are double acting cylinders that can be powered either pneumatically or hydraulically and find usage in applications requiring relatively long strokes and moderate forces and can be operated in limited spaces.

6. Diaphragm cylinders

: These are often used in pneumatic applications and are either of the rolling diaphragm or flat diaphragm-type. They have very low break-out friction with absolute zero leak across the piston.

7. Bellows cylinders

: These are used for very low force applications in sensitive pneumatic control systems. The pressure and the spring rate of the bellows determine the amount of tension and contraction and may be used for basic servo-control systems since metal bellows have a linear spring rate.

Mounting Styles of Hydraulic Cylinders

The mounting style of hydraulic cylinders is an important parameter both from design and maintenance consideration. The various forms of mounting arrangements used are: Plain, Threaded, Clevis, Flange, Tongue or eye etc. Mounting styles for the cylinder body can be: Plain, Foot, Square bracket (single-ended), Square bracket (double-ended), Trunnion-Cap or head-ended, Trunnion-Center, Flange-rectangular or square, Clevis, Tongue and bracket or Tie rod extended.