What Is the Difference Between a Single-Acting and a Double-Acting Hydraulic Cylinder?

What Is the Difference Between a Single-Acting and a Double-Acting Hydraulic Cylinder?

The cylinder, like the hydraulic motor, is an actuator that converts hydraulic energy into mechanical energy. Unlike the engine, which has a rotary motion and transmits torque, the cylinder has a rectilinear motion and transmits a force. The maximum force that a cylinder can exert, neglecting friction, depends on the operating pressure, e.g., on the useful area of piston A: F=p⋅A If a machine has to perform linear movements, the use of cylinders offers a series of advantages: •

Ease of assembly and ease of positioning during the design phase;

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Constant force along the entire stroke;

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Constant speed along the entire stroke, dependent only on the supply flow rate;

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Possibility of generating thrust or traction forces with the same actuator;

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Realization of high-power drives with small overall dimensions.

The tasks entrusted to the cylinders are the lifting, lowering, locking, and moving of a load, but very often, they are coupled with other mechanical parts to give rise to articulated systems capable of carrying out complex movements also, in this case, the cylinders exert the conspicuous forces necessary to operate the mechanism.

What Is the Difference Between a Single-Acting and a Double-Acting Hydraulic Cylinder?

And among all these cylinders, you can find the single-acting, double-acting, and telescopic cylinders, each having a different dimensioning, and therefore the speed and the force vary. This article will reveal the difference between a single-acting and a double-acting hydraulic cylinder.

Single-acting hydraulic cylinder The single-acting hydraulic cylinder is one of the most used among the categories of hydraulic cylinders: the piston and the corresponding rod form a single piece of equal diameter. Only the dynamic seal is required for the rod, and the piston return occurs by external forces. The construction cost is low, but it can only be of the single-acting type.

As its name suggests, a single-acting cylinder is designed to perform a simple action: create a mechanical action and perform a movement in one direction only (usually pushing, sometimes pulling). Once the movement has been carried out, the cylinder returns to its initial position under the effect of the weight.

What Is the Difference Between a Single-Acting and a Double-Acting Hydraulic Cylinder?

To protect the cylinder, a pressure relief valve is generally used. As for the valves, they are used to regulate the flow or block the cylinder in the event of a hose rupture.

Remember that the minimum operating pressure is 20 bar and a maximum of 200 bar (and up to 350 bar on request).

Double-acting hydraulic cylinder The double-acting cylinder, also improperly called a double-acting hydraulic piston, differs from the single-acting one in that it can develop thrust in both axial directions, thus making the piston slide along its axis in both directions. The oil is pushed under pressure both in the thrust chamber and in the pulling chamber and can thus generate movement, ensuring complete control of the system to be governed. It is particularly suitable for attachments that do not allow the piston to return due to the force of gravity alone, for example, because they work in tilting or overturning conditions.

Contrary to what one might think, the double-acting cylinder does not double the minimum operating pressure. No, it is designed to produce two movements. A piston makes it possible to create a forward movement and a return movement.

And so that this movement can be done in both directions, the pressure and the flow are exerted via two supply orifices which alternately supply each hydraulic cylinder chamber. This is how the stem moves in or out, depending on the pressure and flow available. Remember that the minimum operating pressure is the same as a single-acting cylinder.

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