How Does a Hydraulic Cylinder Work?

Double acting hydraulic cylinders are equipped with two ports, respectively on the rod ends and base ends. The function of these two ports is to control the flow and movement of fluid back and forth. The piston retracts when hydraulic oil is pumped into the top port, then the piston will be forced into its original position. On the other hand, the piston extends when pumping fluid to the head end. For projects requiring repetitive accuracy, double-acting cylinder is a better choice because of its faster and predictable shrinkage.

Step 1: The extension stroke:

When hydraulic fluid is applied to the base or end cap of the cylinder, the piston and attached rod begin to move away from the base. This movement is caused by the hydraulic pressure exerted against the surface area of the piston, forcing the piston to slide up the cylinder bore. As the piston moves, the rod extends from the rod end of the cylinder. This movement is utilized for tasks requiring a pushing force.

Stage 2 - The retraction stroke:

Retraction occurs when the direction of hydraulic fluid flow is reversed. Now, the fluid is applied to the "rod end" of the cylinder, moving the piston towards the base and forcing the fluid in the cap end to be pushed out and return to the reservoir. The retraction stroke provides a pulling force and is controlled in speed and pressure just like the extension stroke.

How Do Single Acting Hydraulic Cylinders Work?

In this type, hydraulic cylinders usually include just one port where the hydraulic oil enters and forces the piston out in a singular direction. The piston rod in the cylinder barrel can push outwards but cannot pull back. Thus, it is required an extra pressure in the opposite direction to make the rod back.

Step 1: Hydraulic Pressure for Extension:
Inside the single acting cylinder is a piston attached to a piston rod. When hydraulic fluid is pumped into the cylinder, it enters through a single port and applies pressure to the piston area. This pressure causes the piston to move, which in turn extends the piston rod out of the cylinder body. This motion can do work such as lifting a load or pushing against an object.

Step 2: Retraction Mechanism:
Opposite to a double acting cylinder which uses hydraulic power for both strokes, the single acting cylinder relies on an external force for retraction. This force is usually a spring contained within the cylinder which is compressed during the extension phase. Once the hydraulic pressure is released, the spring's decompression forces the piston back to its original position. In other applications, the weight of the load that the cylinder is supporting can also retract the piston rod once the pressure is removed.

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