Hydraulic pistons are the core of the linear motor

The hydraulic piston is the moving part of a hydraulic cylinder. It performs the desired work when extending and retracting. In hydraulics, this is always vector-oriented. This means that not only is a defined distance covered, but a constant force acts along the path.

How the Hydraulic Piston Works

The hydraulic piston sits centrally in the liner of the hydraulic cylinder. A distinction is made between single-acting and double-acting hydraulic cylinders. In single-acting cylinders, the piston extends in only one direction. For its retraction, an externally acting force, such as a weight or a return spring, is required. A typical example of a single-acting hydraulic piston is found in a plunger cylinder. Single-acting hydraulic pistons consist of a steel cylinder with a constant cross-section.

The vast majority of common hydraulic pistons are designed for double-acting cylinders. They consist of a steel rod with a small diameter, at the end of which round steel discs are attached on both sides.

In a double-acting piston, extension does not differ from the single-acting variant. The hydraulic oil is pumped into the cylinder via a valve. The oil pressure extends the piston with a constant force and speed.

For retraction, oil is pumped into the front of the hydraulic cylinder by switching the valve. From there, it flows against the lower stop disc and pushes the piston back into its rear end position.

Control of Hydraulic Pistons

Hydraulic pistons are limited in their effective stroke by their installation length within the cylinder. In addition to this technically determined maximum limit, a hydraulic piston can also be controlled in its effective stroke by other constructive measures.

Simple stops are less advisable in hydraulics. Since hydraulic cylinders always exert high pressure at their point of action, damage can occur to the stop or the piston itself. Therefore, in hydraulics, as in pneumatics, stroke limitation is preferably set up via end position switches. These are simple electromagnetic proximity sensors. When these come into contact with a pin or with the stop discs of the hydraulic piston, the switches emit a signal. This can be interpreted by a control system as desired. However, the control system usually at least stops the flow to the cylinder. This can be achieved by switching off the hydraulic pump or by switching a valve.

Damage to the Hydraulic Piston and its Repair

Hydraulic pistons are designed for their specific operation. This means that they are very robust ex-works and can handle the forces that occur without problems for a long time. However, they can become pitted due to corrosion or external damage. Bending stresses can also lead to permanent deformations in the piston. Nevertheless, a hydraulic cylinder can be easily overhauled and made operational again by installing new seals and pistons.