Types of Hydraulic Cylinders

Hydraulic cylinders serve as fundamental components in countless industrial and mechanical applications, offering powerful linear force for various tasks. They come in a range of types, each designed to meet specific needs and challenges. Understanding the different types of hydraulic cylinders is crucial for selecting the most suitable option for your application.

Hydraulic cylinders can be classified into several types based on different criteria such as their construction, function, and application.

Types of Hydraulic Cylinders

Hydraulic Cylinders come as either Single or Double Acting. If only one chamber is pressurized by the hydraulic fluid, it is a single acting, otherwise it‘s double acting.

Single Acting Hydraulic Cylinder

In a single acting cylinder, there is one chamber that receives pressurized hydraulic fluid. Which side that is will depend on the intended use of the cylinder. If it is meant for a pushing motion, the chamber opposite the cylinder rod will be pressurized. The other chamber is usually spring loaded to cater for the retraction. If the chamber with the cylinder rod is the one pressurized, it will be a pull motion. The opposite chamber will also be spring loaded to cater for the protrusion.

Advantages of Single Acting Cylinders

Simple to design, manufacture and easy to install
Low cost of initial purchase
Single port (Input) and small housing
Reduces the costs in valve and piping costs

Single Acting Disadvantages

The thrust generated by the cylinder is reduced due to the spring that is supplying an opposite force
When the spring wears off, the strokes of the cylinder will become inconsistent.

Double Acting Hydraulic Cylinder

In a double acting cylinder, both chambers can be pressurized. Of the two chambers, the one that accommodates the cylinder rod will have little surface in contact with the hydraulic fluid, since we cannot take into account the surface area of the piston already occupied by the cylinder rod. This difference in the surface area will need less pressure to retract than the other. Thus, pressure control and direction control is important in this set up of hydraulic systems.

Advantages of Double Acting Cylinders

It has a lot of control over movement considering pressurized air moves both ways
Faster, stronger and use less energy
It offers a variety in design options for stroke and bore sizes
It offers a force in all directions, that is push and pull motions

Double Acting Disadvantages

Costlier than single pneumatic cylinders
They need a bigger housing if used for example as a feed cylinder because of the coupling required.

Hydraulic Piston Configurations in Cylinders

The three most popular hydraulic piston configurations are ram styles, tie-rod, and welded. Tie-rod cylinders utilize threaded steel tie-rods with great strength, usually on the outside of the cylinder casing, to provide additional stability. Welded cylinders incorporate a heavy-duty welded cylinder housing that has a barrel welded right onto the end caps and thus requires no tie rods. Ram cylinders usually have no piston but rather use the cylinder rod as the piston.

Hydraulic Ram Cylinders

Single-acting hydraulic cylinders that have no pistons but have large rods are called rams. These rams operate exactly like the conventional single-acting cylinders. However, they use large diameter rods in place of pistons and piston seals in their designs. Thus, in place of pistons, rams have high-pressure cap-end ports. They also do not have any low-pressure rod-end ports.

Rams are generally cheaper than their conventional single-acting cylinders counterparts.

Ram types of hydraulic cylinders are typically used to give vertical motion, including lifting loads in a vertical direction. Such a cylinder is also used to provide the motion in a horizontal direction but needs attention and suitable guides to guide the motion.

A good example of a Ram cylinder is a telescopic cylinder.

Telescopic Hydraulic Cylinders

Telescopic hydraulic cylinders are also known as multi stage cylinders. Their huge advantage is that it can be a single acting hydraulic cylinder or a double acting hydraulic cylinder or a combination of both. They are a variant of a linear actuator with stages operated in a straight line rather than circular. Telescopic cylinders are typically used in construction trucks, dump trucks, vehicle trailers, and agricultural equipment. The telescopic hydraulic cylinders can be operated with ease, cost effective, space saving and can meet specific angle requirements.

These are a type of linear actuator consisting of a series of tubular rods called sleeves. These sleeves, which are typically 4 or 5, sequentially decrease in diameter.

As the hydraulic pressure is introduced to the cylinder, the main or barrel, which is the largest sleeve, is extended first. Once the barrel has gotten to its maximum stroke, the next sleeve then begins to extend. This will continue until the cylinder reaches the last stage.

Tie Rod Type Cylinder

This cylinder holds the two caps of the cylinder barrel ends using threaded steel rods. Tie rods can number all the way up to 20 depending on the bore diameter and operating pressure. One of the big advantages of the tie rod is it is effortlessly stripped and examined for repair. Tie rod cylinders are used in a large majority of industrial manufacturing applications. Smaller bore cylinders typically have few, maybe four tie rods, whereas larger bore cylinders can have as many as 20 tie rods in order to weather the forces produced by the cylinder.

Welded Hydraulic Cylinder

In a welded rod hydraulic cylinder, often the barrel gets welded directly to the end caps. The head cap can utilize a variety of retention approaches, such as threading or bolting down. This design is generally accepted for mobile equipment because of the compact construction, inside bearing lengths, and its duty cycle compared to tie rod construction. But, this design does make inspection and repairs a lot more difficult in the field due to requiring less common tools and equipment.

The welded rod cylinders are welded and also have loftier seal packages. These help to increase the life expectancy of the cylinder and are helpful when the cylinder will be used in locations that include contaminants and weathering. Visually, these welded body cylinders tend to have lower profiles than tie rod cylinders which improves the appearance of the equipment they are mounted on. Because they are narrower than tie rod ones, welded hydraulic cylinders work well in situations where space is a factor.

Mass of a Hydraulic Cylinder

The initial step is to determine the size of the mass you need to move. As soon as you know how heavy the mass is, you then consider the effect the mass has on the force required to move it. For instance, if a load is being pushed straight up, it will only require a force equal to its weight to lift it, but if it’s pushing a load on the ground, you will have to overcome friction and acceleration. Also note that it is good practice to assume a force 120% bigger than the calculated result for safety.

Geometry Involved

Next, you then need to study the geometry involved in moving it. Machines like a hydraulic press, which reciprocates up and down, the geometry is simple and requires no further consideration.

However, when the center of the load being moved is offset to the point of lift force and at perpendicular angles to that point of lift force, the force required by the cylinder changes. For a crane, for instance, the cylinder pushes on the boom, usually very far from the load. In most cases, distance from the load to the fulcrum can be ten times the lift force and sometimes more. So the closer your lift point is to the fulcrum the more force is needed by the cylinder to lift the load.

Flange mounting is best suited for transferring the load along the centerline of the cylinder. The non-centerline mounting needs support otherwise they misalign.

Bore Size

The next step is to calculate the bore size for the cylinder. The force that the cylinder produces is the product of the system pressure multiplied by the area of the internal piston surface upon which that pressure acts. This is the formula that is used to calculate the bore size required to achieve that force.

The maximum pressure range for the application will also vary the bore size. Pressures can vary greatly depending on the specific job that the system is doing. Cylinders are applicable in test pressure and nominal standard pressure, thus catering to variations. The pressure of the system must never be more than the nominal rated design pressure of the cylinder.

Rod Size

The following step to selecting any hydraulic cylinder should be to choose an appropriate rod size. Most standard cylinders come with either one or two rod options. Choosing the required rod size needs careful consideration of the stroke length necessary which in turn affects the rod buckling strength. On top of rod buckling, bearing loads also is another consideration in the selection of a hydraulic cylinder. Increasing the stroke length of a cylinder also increases the resultant bearing loads on the piston rod.

When deciding on push or pull or both, is double acting, the answer may require a particular double-acting cylinder if the hydraulic system is doing double duty. Since single acting cylinders extend the piston under hydraulic pressure a double acting cylinder will extend and retract the piston under pressure. For a push application, it is very important to size the rod diameter correctly to avoid rod buckling. For pull application, it is vital to size the annulus area or piston diameter area minus the rod diameter area correctly so as to move the load at the rated design pressure of the cylinder.

If selecting from standard cylinder rod options, it is recommended that a smaller rod for a given bore only be used for small stroke push loading or reduced pressure applications, the larger rod given to be used when wanting to obtain maximum dependability and fatigue life of the rod. If it is determined that the necessary rod diameter surpasses that of the biggest available within the selected cylinder bore size, it could then be essential to reconsider design parameters.

When deciding on the required stroke length, if space is not available for the ideal length, a telescopic configuration may be necessary, or even a radial configuration that allows the cylinder to move in more than one axis. Long stroke cylinders often are at risk for twisting or misalignment and need additional support.

Rod End and Base End Types of Welded Hydraulic Cylinders

Welded hydraulic cylinders are robust and commonly used in various applications due to their compact design and ability to withstand high pressure. The ends of these cylinders come in various types, each suited for different applications and mounting needs. Here are the common types of welded hydraulic cylinder ends:

1. Clevis End

Description: The clevis end is a U-shaped connector with a hole for a pin. It allows for pivoting connections and is widely used in mobile and industrial applications.
Common Applications: Agricultural machinery, construction equipment, and material handling.

2. Cross Tube End

Description: A cross tube end has a cylindrical tube welded perpendicular to the rod or cylinder body. It allows for mounting with a pin or bolt that passes through the tube.
Common Applications: Excavators, loaders, and other heavy equipment.

3. Spherical Bearing (Rod Eye)

Description: A spherical bearing end, also known as a rod eye, has a ball joint or spherical bearing that allows for a wide range of motion. It’s used where misalignment is common.
Common Applications: Applications with dynamic loads or where the cylinder needs to accommodate angular movement.

4. Threaded Rod End

Description: This end has a threaded rod that allows for the attachment of various fittings, such as clevises or custom connectors. It’s versatile and allows for precise length adjustments.
Common Applications: Industrial machinery, presses, and custom equipment setups.

5. Flange Mount End

Description: A flange mount end features a flat, plate-like surface with bolt holes, allowing the cylinder to be securely mounted to a flat surface.
Common Applications: Stationary machinery, presses, and heavy equipment.

6. Tang End

Description: The tang end is similar to a clevis but typically has a single tab or lug with a hole for a pin, providing a sturdy connection with less bulk.
Common Applications: Heavy machinery, where space is a constraint.

7. Lug Mount

Description: Lugs are welded or cast onto the cylinder’s body, allowing it to be mounted with bolts or pins. This type provides strong support for the cylinder in both fixed and pivoting positions.
Common Applications: Construction machinery and industrial equipment.

8. Eye Bracket End

Description: The eye bracket end features a solid loop or eye through which a pin can pass, allowing for a secure and often fixed connection.
Common Applications: Heavy-duty industrial equipment and applications requiring minimal movement.

9. Swivel Mount

Description: A swivel mount allows the cylinder to rotate around a pivot point, which is useful in applications where the cylinder must accommodate changing angles during operation.
Common Applications: Construction equipment and mobile hydraulics.

Conclusion: understanding the various types of hydraulic cylinders is crucial for engineers and professionals working with hydraulic systems. By familiarizing themselves with these types, they can make informed decisions when selecting the appropriate cylinder for their specific application. Whether it’s a single-acting, double-acting, telescopic, or other type of cylinder, each has its advantages and limitations. By considering factors such as load requirements, space constraints, and operational conditions, engineers can optimize system performance and ensure reliable operation. Additionally, ongoing advancements in hydraulic technology continue to expand the range of options available, providing even more opportunities for innovation and efficiency in hydraulic system design and implementation.

If you have any additional questions or need help choosing a hydraulic cylinder, do not hesitate to contact Magister Hydraulics customer support.