Hydraulic Cylinders Guide

What Are Hydraulic Cylinders?

Hydraulic cylinders are mechanical actuators used to provide a linear force through back-and-forth movement under pressure. They are so pervasive in the manufacturing industry that it is almost impossible to lay down all of their applications. The use of hydraulic cylinders can span from something as small as chucks, to large-scale construction equipment such as excavators. Hydraulic cylinders serve many purposes, such as providing clamping forces, lifting beds and winches, operating presses, and supporting heavy loads. Read on to find out more about the indispensable hydraulic cylinders.

Figure 1. Hydraulic Cylinders, Ton Fou

Components of Hydraulic Cylinders

A hydraulic cylinder typically consists of the following components:

• Cylinder Barrel (Tube): A cylinder barrel is basically the outer layer of the cylinder which usually has the company logo painted or printed on it. It is typically made of steel. The type of steel used depends on the strength required for the hydraulic pressure. For higher pressure, tougher steel and thicker cylinder walls are used. For maximum corrosion resistance, stainless steel is preferred. 

• Cylinder Rod: The cylinder rod is also one of the external components, but cannot be painted. Therefore, it is normally applied with some smooth coatings for protection. As an external component, a cylinder rod must be resistant to corrosion and  wear. So it is typically made of stainless steel. 

• Piston: The piston is the internal cylindrical component that moves up and down inside the cylinder bore. It is basically the workhorse for creating the hydraulic force. In design considerations, it’s important to make sure hydraulic fluids cannot leak into the internal piston. 

• Hydraulic Fluid: Most hydraulic cylinders use  oil. Different hydraulic systems will require a specific type of hydraulic fluid with a certain viscosity. In others cases where inflammable fluids may pose a risk, a water-type hydraulic fluid is used.

• Seal: Hydraulic seals are an essential component of the hydraulic cylinder which are used to keep fluid from leaving the system. They can be made of various different materials depending on the type of hydraulic cylinder.

The aforementioned are only the core components of a hydraulic cylinder. Other parts that make up the internal portion of the cylinder include ports, cushions, neck glands, butt plates, O-ring, etc. 

Figure 2. Structural Components of Hydraulic Cylinders

Operation of Hydraulic Cylinders

How a hydraulic cylinder works is based on Pascal’s principle. To put it simply, it has a lot to do with the diameter of the piston and the mechanism behind its movement. And the larger the bore, the greater the force generated through the pushing of hydraulic fluids.

To elaborate, a hydraulic system contains two cylinders of different diameters, which have a parallel pipe connection. Each cylinder has two ports for the intake and exit of hydraulic fluids. When applying force on the piston, the fluid is compressed into the smaller cylinder. This forces the fluid from the smaller  to the larger cylinder through the tube, prompting the larger one to move upward with the generated force.

The speed at which a hydraulic cylinder pistons operate is mainly based  on the pressure difference inside the cylinders. When you apply constant pressure to the cylinder, the release valve will relieve the pressure, allowing the piston to move further. Applying this concept, the larger the cylinder diameter, the greater force the system can generate. Check out the video below for a comprehensive illustration of how a hydraulic cylinder operates:

Applications of Hydraulic Cylinders

Hydraulic cylinders have many applications, most notably in heavy-duty construction equipment as we mentioned earlier. They are also found in an extremely wide range of industrial machines, such as turning machines and press machines. The automotive industry also relies heavily on hydraulic cylinders, enabling the production of various car parts that require substantial forces. 

Furthermore, the machine tool sector also utilizes hydraulic cylinders for workholding devices such as chucks. The cylinders are typically installed next to the headstock and the gearboxes. They are also used in compactors, injection molding, and more. In more advanced applications, hydraulic cylinders are used in flight simulators and fatigue testing as well. Summing up, a hydraulic cylinder will always be needed as long as there is any application requiring a strong push or pull force.

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