What Is Hydraulic Cylinder, and What Are Its Types?

Hydraulic cylinders are most often found on agricultural equipment, construction machinery, industrial bodywork, the maritime industry, and even industrial machinery. Basically, it is simply an actuator that creates mechanical linear motion to transmit force and achieve pressure displacement. This article will reveal what a hydraulic cylinder is and what its types are.

What is a hydraulic cylinder?

A hydraulic cylinder is mainly made up of an empty cylindrical body inside which a piston, also known as a rod, generally ground, flows through the effect of the pressure exerted by a liquid. 

Types of Hydraulic Cylinder

According to their functioning, the cylinders are divided into:

• Single-acting cylinders;

• Double-acting cylinders.

Single-acting cylinders

In this case, the liquid, generally oil, enters and exits from one side only, so the force on the stem is applied in one direction only. The cylinder works only by push or pull, and the return of the rod is guaranteed by means of a spring or through the same load. Single-acting cylinders can be with plunger piston or with spring return.

Plunger piston cylinders- This type of cylinder can only carry out a pushing action, and depending on the needs, it can be equipped or not with an internal guide piston. This type of cylinder is used when the existence of a contrasting force of a certain direction guarantees the return movement to the initial position. Therefore, the exit phase is made possible by the action of the oil pressure on the piston surfaces, while the action of an external force guarantees the return phase.

Spring return cylinders- This type of cylinder is used when there is no external force to guarantee the return phase: this phase is therefore guaranteed by the action of a spring, which, depending on the construction method of the cylinder, can act either in the exit phase of the piston or in the re-entry phase. The opposite phase, i.e., the one in which the cylinder carries out its motive action, is ensured by the action of the oil under pressure.

Double-acting cylinders

In double-acting technologies, on the other hand, the cylinder is equipped with two threaded holes which represent the delivery and discharge of the liquid, allowing the piston to work both in thrust and in pulling. There are different types of double-acting cylinders:

• Differential cylinder;

• Synchronous cylinder;

Differential cylinders- The double-acting differential cylinder has two opposite useful surfaces of different sections and is equipped with two supply connections. A thrust or traction force is transmitted to the piston and a consequent outgoing or re-entering motion by feeding one of the two connections with pressurized fluid.

The cylinder is called differential because the two useful sections are different. This entails a different behavior of the cylinder in the outgoing phase of the piston and in the re-entry phase.

In the exit phase, since the pressure acts on the greater surface, there will be a greater force than in the return phase; on the contrary, the speed will be greater in the return phase because the same flow will act on a smaller surface.

Double rod cylinder (synchronous cylinder)- The two-rod cylinder is obtained by connecting two rods of the same or different diameter to the piston, in any case, smaller than that of the piston. The maximum force developed in both directions is given by the product of the respective annular areas and the operating pressure.

If the diameters of the two rods are the same, so are the annular areas on the two sides of the piston, so that at the same pressure, the forces developed in both directions are equal. Furthermore, since the annular areas are equal, with the same flow rate introduced through connections A and B, equal speeds develop in both directions, hence the name of the synchronous cylinder.

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