Hydraulic cylinders are heavily used in industrial and automotive applications around the world. The metal tubes are essential for transporting mechanical force across distances and for converting fluid pressure to physical movement. There are two main types of cylinders used today, single acting and double acting, and it’s important to understand their differences to understand which option is right for a specific application.
How Does a Hydraulic Cylinder Work?
A hydraulic cylinder is a tough metal tube with a rod and piston inside. The tube fills with pressurized hydraulic fluid that presses on the piston, extending the rod out of the tube and applying horizontal force to something external. The only job a hydraulic cylinder has is to convert fluid pressure into mechanical movement, and that movement can raise heavy machinery, convert internal combustion forces in an engine into motion that helps move a car down the road, and more.
Single Acting Vs. Double Acting Cylinders: Structural Differences
While single-acting and double-acting cylinders rely on the same technology, there is one key difference that changes how they function. In a single-acting cylinder, there is only one port where fluid flows in, raising the pressure and moving the piston. In a double-acting cylinder, there are inlets on either side of the piston, making it possible to extend and retract the rod by directing the flow of hydraulic fluid back and forth.
Single Acting Cylinder
Double Acting Cylinder
Benefits of Single-Acting Cylinders
There are several real-world benefits that come from single-acting cylinders that make them more common than double-acting varieties.
- Simple Construction
- Affordable to Purchase
- Compact Design
- Simple to maintain
Single-acting cylinders make use of basic construction and are much more affordable to purchase. Since these cylinders rely on more simplistic mechanisms, they can be made more compact and used in applications where space is limited. They are easy to understand and there are fewer moving parts to worry about, making them easier to maintain overall.
Single-acting cylinders are used in situations where force only needs to be generated in a single direction. They work well for lifting applications, for applying steady pressure, for moving materials upwards, and much more.
Benefits of Double-Acting Cylinders
While double-acting cylinders are more costly and complex, there are situations where they are the best option thanks to the benefits they offer.
- Can apply force in two directions
- Enhanced control
- Enables precise movements
- Faster movements
- More efficient operation
- Long-term reliability
Double-acting cylinders provide precise movement control that isn’t possible with single-acting varieties. Instead of relying on spring pressure or weight to retract the rod after it’s extended, a double-acting cylinder applies pressure to retract the rod at a specific speed and with a certain amount of force. When precision control is required, a double-acting cylinder is an important upgrade.
Along with being more controlled and precise, these specialized cylinders can move back and forth faster than single-acting options, making them faster and an essential upgrade when completing as many cycles as possible is important. Double-acting cylinders are also more reliable because they utilize durable hydraulic pathways for movement rather than springs or other methods that will eventually wear out.
Double-acting cylinders are used in environments where significant forces are required along with precision movements. Things like dump truck bed lifts and CNC machines both depend on the highly-controlled movements that are possible with double-acting cylinders.
Single-Acting Vs Double-Acting Quick Chart
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Standard Versus Double-Ended Double-Acting Cylinders
Single and double-acting cylinders offer different real-world performance characteristics, but there are different types of double-acting cylinders to be aware of as well. There are the standard cylinders with a single rod, and there are specialized double-ended cylinders that come equipped with two different rods that move in opposing directions.
When Double-Ended Cylinders are Useful
While standard double-acting cylinders are often enough to meet the needs of a user, there are specific situations where double-ended cylinders are the superior option. These cylinders retract and extend their rods at a constant rate, unlike standard double-acting cylinders that retract faster than they extend. For scenarios where consistent speed is important, these special cylinders are a useful upgrade.
Why Standard Double-Acting Cylinders Move at Varying Speeds
In a double-acting cylinder like the one above, the rod is pressed out more slowly than it retracts back in. This is because there is only a rod on one side of the piston. In order for the piston to move, fluid must be pumped into the cylinder on one side or the other. Only once enough fluid builds up will the piston begin moving the rod. On the side of the piston where there is no rod present, there is more space for fluid. With more space to fill it takes longer for fluid to flow in before movement can occur, which is why the rod extends out more slowly than it retracts. For the rod to retract, the side of the piston with the rod must be filled with fluid. Since the rod is taking up some of the space to push the rod side of the piston, the space fills faster, and the rod retracts in less time.
There are also some situations where it’s beneficial to have two sets of rods to make use of. When having rods moving in two directions is important for driving multiple applications, then a double-ended cylinder is worth considering.
It’s important to note that double-ended cylinders are more complex and costly than standard double-acting cylinders. Many buyers avoid this specialized equipment unless they have a strong reason to make the upgrade.
Conclusion
Hydraulic cylinders are essential components on most types of machinery today, but not all cylinders feature the same design, and some applications are best-suited by single-acting cylinders while others require double-acting cylinders. With a better understanding of how the two varieties of cylinders work and what benefits each offers, you should be able to select the option that will best meet your needs.
