Hydraulic cylinders lift, push, pull, compress, and extend with a tremendous amount of force. We know how indispensable they are to your compact equipment, so here's a refresher on the basics.

Parts of a Hydraulic Cylinder

Let’s start by taking a look at the basic components that make up a hydraulic cylinder.

The barrel is a strong, seamless cylindrical tube containing the piston and piston rod and is engineered to handle extremely high internal pressure.  Also known as the end cap, the cylinder head cap attaches to the piston rod and serves as an end seal for the barrel. The piston is a disc-shaped component that moves back and forth inside the barrel and translates hydraulic pressure into force that moves the piston rod. 

The piston rod is a strong, stiff solid metal rod connecting the piston to the external load. It has to be designed so that it doesn’t buckle under heavy loads, which includes its diameter, length, and the material used for it. Sometimes referred to as the wear band or wear ring, the rod bearing band prevents metal-to-metal contact between moving parts and helps maintain the piston's alignment.

There is also the rod end: the point where the piston rod extends from the cylinder and is usually connected to the component that is supposed to be moved by the cylinder.  A welded rod end can be seen below. The base end is the fixed mounting point that attaches the cylinder's base to the equipment. It is on the opposite end of the rod end.

Rstom03, CC BY-SA 3.0 via Wikimedia Commons (Source)

The ports are locations where hydraulic fluid enters and exits the system, while the seals keep hydraulic contamination out and hydraulic fluid inside. Here are some of the key seals in a hydraulic cylinder:

• Rod seal: This can be found in the cylinder head and creates a barrier around the piston rod to keep contamination out and hydraulic fluid in
• Wiper: Works with the rod seal to “wipe” contamination off the rod

• Piston seal: fitted directly onto the piston and creates a robust seal between the piston and the barrel

• O-ring: works with the piston seal

Types of Hydraulic Cylinders

Here are the types of hydraulic cylinders typically found on construction equipment.

Single-Acting Cylinders

These apply pressure in only one direction (usually to extend a rod) and are commonly found on hydraulic jacks and dump trucks.

Double-Acting Cylinders

These hydraulic cylinders can apply pressure and force by extended and retracting in both directions. Backhoes, excavators, and bulldozers use them extensively. This type of cylinder gives an excavator the power to dig, push material away, and pull material in.

Via Wikimedia Commons (Source)

Telescopic Cylinders

These cylinders exhibit telescoping action, with multiple-stage cylinders that extend sequentially. One of their benefits is the ability to provide a long stroke while maintaining a compact design. Cranes and dump trucks , such as the one shown below, use them to achieve very long extension strokes. 

Cjp24, CC BY-SA 4.0, via Wikimedia Commons (Source)

Tie-Rod Cylinders

On agricultural equipment you’ll often see tie-rod cylinders that have strong threaded steel rods to hold the rod and cylinder end caps together.

Welded Cylinders

On welded cylinders the end caps are welded onto the cylinder barrels and work extremely well for high-pressure applications in construction and mobile equipment. They are very strong because the end caps are welded rather than bolted on.

Rstom03, CC BY-SA 3.0 via Wikimedia Commons (Source)

Mill-Type Cylinders

These cylinders have thicker walls and flanges to make them effective for harsh working environments and high-pressure applications. They are found on heavy-duty equipment and will resemble the one shown below. As you can see, they are definitely heavy duty.

Rstom03, CC BY-SA 3.0 via Wikimedia Commons (Source)

Ram-Type Cylinders

Ram-type cylinders are going to have a large-diameter rod and a small cylinder. They are used mainly for applications requiring pushing forces, like jacks or hydraulic presses.

Differential Cylinders

Finally, there are differential cylinders. These are pretty cool: the effective areas for the piston to work on are different for extension and retraction, which means they can retract more quickly than other hydraulic cylinders.

Conclusion

If the hydraulic cylinders on your equipment wear out of just fail, then your machine can still move but there's a limit to how much work it can do. If your machine comes to a grinding halt, then it's time to conact Texas Final Drive for a new final drive motor.