What are the different types of hydraulic cylinders?

Hydraulic cylinders can be classified into a number of major categories, based on the structure and purpose that include double-acting and single-acting (by the actuation method) tie-rods, welded-body and telescopic cylinders (by construction), and specific designs like plunger/ram and differential cylinders. They also have multi-stage telescopic cylinders that have a longer reach. The choice of cylinders depends on load direction as well as duration of the stroke, mounting limitations, and the duty cycle.

Hydraulic cylinders convert the pressure of fluid into a linear force and are the engine for everything from booms of excavators to industrial presses. However, "hydraulic cylinder" isn't one design; it's a class that encompasses a variety of distinct designs that are each designed to meet various stroke, force, and mounting needs. The wrong choice could cause premature seal wear or a stroke that isn't long enough or a cylinder that isn't able to take on the load direction that the application requires. This guide explains the main cylinder types according to their actuation technique, design style, and the specific usage case, so that you can find the best design for your application.

Classification of actuation types based on type

Single-acting Cylinders

Single-acting cylinders make use of hydraulic pressure to expand the piston only in one direction. Retraction occurs through external force, which is usually gravity, a spring, or even the weight itself. The cylinders are equipped with only one port and a more compact internal design that makes them less expensive to build and less susceptible to failure of certain types of seals because there's no requirement to seal against the pressure of each side of the piston.

The most common applications are bed-for-dumps or jacks as well as liftgates. The weight of the load provides an effective return stroke. This means that you have a restricted control over the speed and force that is based on the forces of gravity or springs instead of controlling the motion hydraulically.

Double-acting Cylinders

Double-acting cylinders feature two ports, with one port on each side of the piston. This allows the hydraulic force to control both the extension and retract strokes. This allows precise control of the movement in both directions. It also permits the cylinder to perform a job on return strokes, not only that of the extension.

Double-acting cylinders are most commonly used in all applications that require controlled powered movement in both directions, such as press brakes, excavator arms, and steering systems. Since both chambers are exposed to the cycle of pressure, seal selection and rod surface finish play a role more in this regard. Asymmetric wear in the cap-end and rod-end seals can be an issue that can lead to failure if the system isn't properly balanced.

Classification through construction

Tie-rod cylinders

Tie-rod cylinders are made of steel rods that run across the entire length of the tube. They are which are clamped between the caps at the ends in order to keep the cylinders to each other under pressure. The design can be repaired; it is possible to disassemble the cylinder, change seals, and reassemble it without the need for special equipment, which makes tie-rods popular in mobile and industrial hydraulic systems, where field maintenance is important.

The result is a bigger footprint and a more sensible pressure ceiling. Most tie rod designs are at 3,000 to 5,000 psi, and beyond that, the tie rods themselves can become a deterrent aspect.

Welded (mill-type) Cylinders

The end caps of cylinders are welded directly onto the barrel, rather than tied by tie rods. This produces a more compact, higher-pressure-rated design—often suited for pressures well above what tie-rod construction can handle—and a smoother external profile that resists debris accumulation in harsh environments.

The disadvantage is that it's repairable. The cylinder that is welded isn't able to be disassembled to replace seals on the spot. If seals fail, the whole barrel assembly or cylinder typically requires replacement or factory reconstruction. They are typical in agricultural and construction equipment, where small dimensions and pressure capacities outweigh the concerns about field serviceability.

Telescopic Cylinders

Telescopic cylinders are stacked with several stages (sleeves) within one another and extend in a sequence to reach a stroke length that is much greater than the cylinder's length when it retracts. A telescopic cylinder with three stages could retract under a meter but can extend up to around two or three times the length.

They are crucial wherever they are required in situations where a long stroke and a small retracted length are both important, such as dump trailers, aerial lift booms, and telehandlers. The downside is more complicated sealing (each stage comes with an individual sealed set), and the force curve changes when successive stages expand, as each stage has a smaller piston area than that preceding it. To determine the size of telescopic pistons, you must calculate the capability of the most compact stage, as that's the only factor that determines the force output when fully extended.

Specialized types of cylinders

Plunger (Ram) cylinders

Plunger cylinders, sometimes referred to as "ram cylinders," use the piston rod that has an approximate diameter to the bore's diameter. In essence, there is no separate piston head, and the rod acts as the part that is a pressure-bearing component. Because there's no annular region for retraction, plunger cylinders are essentially single-acting and depend on force or gravity to retract.

Their principal benefit is their mechanical simplicity and endurance when side-loaded, which makes them popular in elevators, oilfield pumping units, and vertical lift systems where the rod can handle radial loads that might harm a standard piston-and-rod combination.

Differential Cylinders

When a cylinder is a "differential," the rod-side and cap-side areas of the piston are not equal (which is also the case for the majority of double-acting cylinders that are standard because the rod is some of the piston's area). " "Differential" circuits make use of the difference in area—regenerative circuits, for instance, allow the discharge of the rod back into the cap-side outlet while extending, thereby increasing extension speed, but at the expense of the force available. It's not a distinct physical cylinder design but rather an element of design It's a good idea to know when deciding on cylinders to be used in speed-critical applications, such as speed-approach press cycles.

Tandem cylinders

Tandem cylinders join two or more assemblies of pistons and barrels together on a single rod, effectively adding the power output from each of them without increasing the bore diameter. These are utilized when the space limitations limit how big the bore size is feasible; however, the application requires high force output, which is common in airplane flight control actuators as well as specific press applications.

Cylinders that are cushioned

Cushioned cylinders include an acceleration mechanism at the end of the stroke, usually an elongated plunger that limits the flow of fluid out of the cylinder as it is nearing the cap to slow down the piston before it reaches the cap's end. This helps reduce shock load as well as noise and wear towards the end of the stroke and extends the life of the cylinder as well as the lifespan of the mechanical linkage that is connected to it. The cushioning is adjustable or fixed and adjustable, with the possibility of the field being tuned for deceleration rates.

Selecting the best type of cylinder

Selection is generally based on four key questions:

1. Does the program require powered forces in both directions, or is it a matter of gravity/spring return? This is the determining factor for single-acting vs. double-acting.
2. What's the required stroke-to-retracted-length ratio? A long stroke within an envelope that retracts is a reference to telescopic designs.
3. What's the operating temperature? In addition, is serviceability for field use important? Larger pressure and smaller dimensions favor welded construction. Simpler maintenance is a benefit of tie rods.
4. Does the rod have to endure significant side loading? Plunger/ram cylinders are able to handle the radial load better than conventional rods with pistons.

The cylinder's type and operational requirements in advance help avoid costly retrofits and decrease the risk of a rod or seal leaking and premature failure later on.

What's the most significant difference between double-acting and single-acting hydraulic cylinders?

Single-acting cylinders employ hydraulic pressure only for extension and rely on gravity or a spring to power retraction, whereas double-acting machines utilize hydraulic pressure to drive both the retraction and extension strokes.

What causes telescopic cylinders to lose force as they grow?

Each successive stage in a telescopic cylinder features an effective piston area that is smaller than the previous stage, and the force output decreases with each stage. System pressure has to be adjusted around the smallest stage to allow for sufficient force when fully extended.

Can the cylinder with a weld body be repaired in the event that a seal fails?

The majority of the time, welded constructions don't allow for disassembly, and a damaged seal is usually replaced with a barrel or the entire cylinder is sent to a repair facility for a factory rebuild, in contrast to tie rod cylinders, which can be disassembled in the field.

When should I select the plunger (ram) cylinder instead of a conventional piston cylinder?

Plunger cylinders are preferred in situations that require substantial side-loading or radial forces to the rod, for instance, horizontal lift and well-pumping, because the rod's thickness can withstand side loads that could cause damage to a piston rod assembly.

What is a cushioned cylinder doing differently at the conclusion of its stroke?

A cushioned cylinder limits the flow of fluid near the end of the stroke with the tapered plunger, slowing the piston prior to it contacting the cap's end and thus reducing shock load and noise. It also reduces wear.