Feb. 24, 2025
Machinery
Hydraulic cylinders are an essential component of the hydraulic industry. Almost all the applications use a hydraulic cylinder for converting incompressible hydraulic fluid energy to work. So, having adequate knowledge of this topic will be a great benefit. This article provides you, all the essential information like types, applications, and specifications of hydraulic cylinders.
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A hydraulic cylinder is a linear actuator used for creating a mechanical force in a straight line either through pushing or pulling. A tube, a piston and ram, two end caps, and suitable oil seals are the basic components required for hydraulic cylinder construction. The tube will be having finished interior and hard chrome-plated piston rods are commonly used for avoiding pitting and scoring. Seals and wipers are attached on the end caps for eliminating contaminants and preventing leakages.
Mobile applications such as excavators, dump trucks, loaders, graders, backhoes and dozers use hydraulic cylinders. Other hydraulic cylinder uses are heavy machinery, gym equipment, boats, wheelchair lifts and a lot more. The hydraulic cylinder helps the wheelchair lift to balance the load on it. In the case of heavy machinery, hydraulic cylinders will help to extend the control or usage of equipment.
You can find a vast variety of hydraulic cylinders in the market. The difference in the design of cylinders differs from its applications and industry. The common differences include wall thickness of tube or end caps, the methods used for connecting end caps, the material used, the operating pressure, and temperature. Single acting cylinders, double acting cylinders, tie-rod, welded rod, and telescopic are important cylinder types.
The head end port of these cylinders will operate in a single direction. When the fluid gets pumped into the cylinder barrel, it will extend the piston rod. For generating the return operation(convert to non-pressurized state), a load string or any external force is required. Here, on applying energy, the fluid will drain from barrel to the reservoir. A hydraulic jack is an example of a single acting cylinder. Spring-extend and spring-return are the two types of single acting hydraulic cylinder. The spring-extend, single acting cylinders are used for holding workpieces for a long time. A hydraulic pressure released brake is an example of this type. The commonly used variety of single acting cylinder is spring-return(material handling applications).
In double acting cylinders, both the head and rod ends contain ports for pumping fluids. These ports will control the flow of fluid and provide movement in both directions. Pumping hydraulic fluid to the rod end will retract the piston rod and pumping fluid to the head end will extend the piston rod. Most of the raising and lowering devices are applications of this type. The opening and closing drawers of presses and chippers is a good example of double acting cylinders. Differential and synchronous types are the two categories of double acting cylinders.
Also Read: Is hydraulic fluid flammable
Most of the industrial and manufacturing applications use tie-rod cylinders. The advantages of the tie-rod cylinder include ease of maintenance, repair, and assembling. For holding the end caps of tie rod cylinders, threaded steel rods are used. These end caps will prevent fluid leakages. Depending on the applications, it can use 4 to 20 tie rods.
This type of cylinders weld end caps directly to the barrel. So, they are difficult for assembling and disassembling. The compact construction, internal bearing lengths and duty cycle of welded rod cylinders make it suitable for mobile applications.
This is a single or double acting cylinder. Telescopic cylinder contains more than five tubings nested inside each other. These nested tubings are called stages and the diameter of each nested tube will become lesser.
This article will give an in depth discussion about hydraulic cylinders.
The article will give more detail on topics such as:
What is a Hydraulic Cylinder?
Types and Piston Configurations of Hydraulic Cylinders
Design of Hydraulic Cylinders
Considerations for Choosing a Hydraulic Cylinder
And Much More'
A hydraulic cylinder is a tube that produces linear actuation utilizing hydraulic pressure. Basically, the pressure of a hydraulic fluid forces a piston to move in either a pushing or pulling motion.
This takes advantage of the following laws of physical science:
Hydraulic fluids are incompressible.
In a fluid at rest in a closed container, a pressure change in one part is transmitted without loss to every portion of the fluid and walls of the container. (Pascal's Law)
\begin{equation} \ Pressure = \frac{Force}{Area} \end{equation}
To implement a system that takes advantage of the facts above, a system as shown below can be set up.
Because hydraulic fluids are incompressible, the plungers A1 and A2 will remain in the same positions if no force is exerted on any of them. But if a force is exerted on one of them, we will notice a displacement on the other end because of a resultant force calculated using Pascal's Law as follows.
The pressure on the left plunger with Area A1 and Force F1 is given by:
\begin{equation} \ Pressure_{1} = \frac{F_1}{A_1} \end{equation}
But if pressure is transferred equally through the fluid, then it means this pressure is also the same with pressure at the right side:
\begin{equation} \ Pressure_{2} = \frac{F_2}{A_2} \frac{F_1}{A_1} \end{equation}
Thus it's also true that:
\begin{equation} \ F_{1} = \frac{A_1}{A_2}F_2 \end{equation}
So the force on the other end is equal to the applied force multiplied by the proportions of the areas. The displacement can then be calculated easily going forward since the force is already given.
Hydraulic cylinders are the moving force in many commercial as well as industrial manufacturing concerns. Some of their applications are as detailed below:
Aerospace: Landing gears and wing flaps
Automotive: Earth Moving Equipment
Agriculture: Tractors
Civil works: Excavators, Bulldozers, and attachments
Oil and gas industries
Power Generation: Flow controls for the water gates
Motorway repairs and maintenance
Mining: Excavators
This chapter will discuss the types and piston configurations of hydraulic cylinders.
Depending on the application and industry, hydraulic cylinders can be called hydraulic actuators or hydraulic pistons. These terms can be understood in the following contexts:
Pneumatic actuators are typically used in controlling processes that require an accurate and quick response. This is because pneumatic actuators do not need large motive forces.
In instances where large amounts of force are needed to operate a valve e.g., valves of a mainstream system, hydraulic actuators are the preferred choice. Hydraulic actuators come in various orientations but the most common is the piston type.
These hydraulic cylinders can have different sizes with unique purposes based on the size, for example:
Small hydraulic cylinders have a stable structure, are easy to operate and can be used for a much extended period of time. They are typically used in fast motion applications as well as in equipment with intricate and small components.
The hydraulic cylinders can also be made of different materials, for example:
Stainless steel hydraulic cylinders are typically used in applications where the priority is corrosion resistance. The vast majority of other hydraulic cylinders are made from alloy steel combinations such as and . However, they are prone to oxidation and rusting when used in wet or humid environments. The carbon steel cylinders can still be prone to dents, surface abrasion, or harsher chemicals, even if they may be painted using epoxy. Thus, such conditions can wear away the paint and expose the carbon steel to corrosion. Therefore, in such instances stainless steel hydraulic cylinders are preferred, for example in marine environments both onshore and offshore. These can be used on maritime cranes, davits, or boat lifts.
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.
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.
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.
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.
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.
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There are various components that make up hydraulic cylinders. These components will be discussed below.
This is the main case of the cylinder. Made of steel, commonly carbon steel, the barrel or cylinder tube is built to withstand hydraulic fluid pressure inside its walls throughout its lifespan. A wide variety of steel qualities are available that offer ruggedness and strength, but basically greater pressures will require thicker cylinder walls and stronger steels.
To prevent corrosion and abrasion, the surfaces are given special treatment. Either these will be coated or painted. Some applications of hydraulic cylinders like food packaging might need a material without coats to avoid peels falling into the food, thus stainless steel can be employed in such cases. The internal walls usually need no surface finishing because the hydraulic liquid is usually non corrosive and also protects it from corrosion. However, in some cases where water is used as the hydraulic fluid, coating may be required on the inside walls as well.
This is the part that protrudes out of the barrel. It is attached to the piston inside the cylinder. Because of the friction from the rapid protruding and retracting, this is the only external component that is not painted. Because of its function, not only does it need protection from corrosion, but wear and pitting. This is a very delicate component because peeling, pitting, or corrosion will most likely scrap the seals, contaminate the hydraulic fluid and eventually jeopardize the whole hydraulic systems.
So, the materials and coating of the hydraulic cylinder are of the highest importance. Usually, the cylinder rod is machined from steel or stainless steel and then coated with Hard Chrome Plating (HCP). Nevertheless, many coatings that wear slowly have been adopted, for example COREX. This is a coating that can be up to ten times less porous than HCP, and offer a hardness of up to Hv, almost twice the hardness of HCP. If the rod is working in extreme environments that are highly susceptible to corrosion, a material like Inconel can be employed to make it.
The piston is the disk that separates the two chambers of the barrel. It is the one that is pushed by the hydraulic fluid. The piston is connected to the cylinder rod. Thus, the movement of the piston is seen by the way that the rod is moving. It is very important that no hydraulic fluid passes over the piston. To make sure of this, the piston is fitted with seals, usually U-seals. It must also not wear as it reciprocates, so it also comes fitted with wear rings.
This probably is the weakest aspect of a hydraulic system. Good seals can reduce friction and wear, which then lengthens service life, while bad seals can lead to downtime and frequent maintenance.
Seals are used all over the hydraulic cylinder. These are fabricated of a wide variety of different materials, considering their intended use in the cylinder and the type of cylinder they are in. It is crucial that these be slow to wear, capable of surviving multiple repetitions of the rod moving in and out of the barrel, removing any contamination.
The cylinder designers will select the perfect seal for a specific cylinder application. This they do by taking a number of factors into consideration. Cylinders destined to function in areas with high temperatures require seals that will not melt. For such operations, a common material used is Viton. Cylinders that will be working in extremely cold conditions will need seals that will not harden and crack. Polyurethane is a popular material selected for these applications.
Also, for situations that require quick repetitions, like applications in factories, Zurcon and PTFE seals are often picked. Specialist seals are also common, like ones that get back up rings if these are going to be working under intense pressure. For thin hydraulic fluid that can easily pass over the piston or cylinder end caps, seals with extremely tight closure will be employed.
Some commonly used seals are detailed below.
Rod Seal
The rod seal is the most important seal in hydraulic cylinder application. It is subjected to the harshest conditions in its service. It often sees the most pressure variations and spikes in the system. Its failure can result in fluids leaking into the working environment and can endanger both performance and safety.
It is used to:
Keep the fluid inside the cylinder as it acts as a pressure barrier
Regulate the fluid film to inhibit rod corrosion and to lubricate the rod seal and wiper seal
Take back in, the lubrication film into the cylinder during the retracting of the rod
Buffer Seal
Buffer Seals are commonly used together with another rod or piston seal. Typically, this will be a U-Cup style seal. In many rod applications, they are designed to absorb pressure variations when working under high load conditions. This serves to lengthen the lifespan of a rod seal. Basically the buffer seal functions are to:
Defend the rod seal from fluid pressure extremes in system pressure.
Weaken the variations in system pressure, thus improving rod seal performance by allowing the rod seal to handle more constant or gradually altering pressure.
Behave as an interior excluder to keep system pollutants, such as metal particles, from damaging the rods.
Piston Seal
Piston seals create a sealing force against the inner wall of the cylinder and inhibit fluid from flowing over the piston head into the opposite cylinder chamber. In holding the pressurized fluid from escaping into the other chamber, pressure builds up on one side of the piston, this makes the rod extend or retract.
They are either single-acting piston seals, which means the stress acts only on one side, or they can be double-acting piston seals, meaning the stress acts on both sides.
Wiper Seal
Eliminate external pollutants from entering the Hydraulic Cylinder and accept the lubrication film back into the cylinder when the rod pulls back. The wiper seal is the most underrated seal type in the hydraulic cylinder relative to its significant use.
A Hydraulic fluid is a non-compressible oil or liquid which will be used to transfer power within hydraulic machinery and equipment.
This hydraulic fluid can be made of many elements but it is mainly mineral or petroleum based, water based or synthetic.
It is very important that the fluid be incompressible to have an efficient hydraulic system. These fluids can be:
Petroleum-based or mineral-based fluids
Petroleum-based or mineral-based fluids are the commonly used fluids today. They commonly provide a low-cost, high quality, readily available selection. The properties of a mineral based hydraulic fluid are dependent on the additives, quality of the virgin crude oil, and the process that refined it. Common hydraulic fluid additives include rust and oxidation inhibitors (R&O), anti corrosion agents, demulsifiers, anti-wear (AW) and extreme pressure (EP) agents, VI improvers, and defoamants. Additionally, the lubricants can contain colorful dyes, which help in identifying leaks. Because leaks in hydraulics are so costly, this minor characteristic is important in extending the life of the equipment and saving money and resources.
Water-based fluids
Water-based fluids are not as cost-efficient as petroleum-based fluids. They have drawbacks which include the lowering of wear resistance. This must be weighed in contrast with the advantage of fire-resistance. Fluids based on water are used for fire-resistance due to their high-water content. They are usually available as oil in water emulsions, water in oil emulsions, and water glycol blends. Water based fluids can provide appropriate lubrication characteristics but need to be monitored closely to avoid problems. Since water based fluids are used in applications where fire resistance is desirable, these systems and the atmosphere around the systems can be hot. High temperatures can cause the water in the fluids to evaporate, which raises the viscosity. Sometimes, distilled water will have to be added to the system to rectify the balance of the fluid.
Synthetic fluids
Further reading:The company is the world’s best Multi Stage Hydraulic Cylinder supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
Synthetic fluids are man-made lubricants that offer excellent lubrication characteristics in high pressure situations as well as high temperature systems. Synthetic fluids have advantages like:
They are fire-resistant e.g phosphate esters
They lower friction
Thay have thermal stability
The drawback to these types of fluids is that they are usually costlier than conventional fluids, they may be slightly toxic and need special disposal, and they are usually not compatible with standard seal material.
Hydraulic fluid enters and exits the cylinder through ports, with one port at either end of the cylinder tube and the hydraulic piston between the two ports. These have to be secure, as a weak port can cause a dangerous hydraulic fluid leak under intense pressure.
Cylinder mountings are generally grouped into three categories:
Center line mountings that absorb force on the centerline of the cylinder.
Foot mountings that absorb force eccentric to the centerline of the cylinder.
Pivot mountings that allow the movement of the cylinder body while the piston rod is in motion.
The two ends of the hydraulic cylinder require a mounting interface; the one at the base and the other one at the head.
Center Mountings
Centerline mounts are the preferred mounting method. These mountings exert tensional or shear force against the mounting bolts. Centerline mounts are not flexible and require precise alignment with the load. A well aligned mount cylinder has little rod bearing and piston loads, making it have a longer life. The head mountings are recommended for use in pull stroke applications. Push stroke applications can use the mountings on the piston rod end of the cylinder.
Foot Mountings
Foot mounting secures the cylinder along its side. Since the mounting surface plane is offset from the line of force, mounting bolts are subjected to a significant amount of shear stress.
The cylinder needs to be pinned or keyed to weather the stress of shear loads and allow the mounting bolts to remain in tension.
Key mounts with keyways can be cut into a machine. The mounting accommodates shear loads. They provide accurate alignment of the cylinder and simplify installation and servicing.
Just one end of a cylinder must be keyed to the machine. When ends are keyed, it will result in an unequal distribution of internal stress and deformation. This mainly applies to long stroke cylinders, where performance and life may be dramatically reduced.
Pivot Mountings
Clevis, spherical bearings, and trunnion mounts are common configurations in pivot mountings. Pivot mounting can be utilized when the application requires the load to travel in a curved path. Thus, clevis and trunnion mounts allow this motion. Pivot mounts can help mitigate the load misalignment.
Trunnion pins are made for shear loads only. So, only trunnion bearings that have a tight fit and support the whole pin length must be used.
Some of the considerations when choosing hydraulic cylinders are:
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.
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.
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.
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.
If the bore, the rod, and the stroke sizes have been determined, the other aspect to be considered is whether internal cushions at the end of the cylinder stroke are necessary. Usage of cushions is recommended for the deceleration of high speed rods to reduce the energy of the impact of the piston assembly against the cylinder end cap. Usage of cushions will not affect cylinder envelope or mounting dimensions.
When deciding on how much support the piston and cylinder need it all depends on the stroke length, a stop tube which are necessary to stop excessive wear and jack knifing. However, a stop tube will not prevent rod bending; an oversize rod may be required, based on Euler calculations. The most common error in hydraulic design is underestimating the specification of the piston rod, making the cylinder more prone to stress, wear, and failure.
As much as hydraulic cylinders are rugged when they are working, they require great attention to detail when selecting one for use. An understanding of all components and their functionality is imperative in the design or selection of a hydraulic cylinder.
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There are several types of hydraulic cylinders that you may encounter. Hydraulic cylinders are commonly used in applications that move heavy loads and require a significant amount of force. Hydraulic cylinders are simple, durable, and create a massive amount more force than pneumatic, mechanical, or electrical systems. In comparison, a hydraulic pump has about ten times the power density of an electrical motor's similar size. There are an impressive array of cylinders available to choose from to meet the wide range of industrial demand.
Selecting the right kind of cylinder for an application is critical. That means taking into consideration several parameters. Fortunately, there is an assortment of cylinder types, mounting techniques, and 'rules of thumb' available to guide you.
There are few necessary details to consider when starting a design project for a custom cylinder. The first thing is to understand the operating environment in which the cylinder will be working. Factory environments most often are stable and working steadily compared to forestry environments, where the cylinders may encounter the risk of rupture.
When designing hydraulic cylinders for various environments, one has to remember that some cylinders are designed to last 50 000 cycles as others are designed to last a million cycles. It depends on the customer's specification of what the cylinder's lifetime needs to be.
The frequency of cylinder use is one of the critical factors to consider. How many cycles does the cylinder operate daily, monthly or yearly use? Does the cylinder constantly run during the day or just occasionally?
The pressure variations impact hydraulic cylinders' fatigue life and are one of the significant factors to consider. The pressure rises and lowers smoothly in steady work, but the pressure variation might have massive regulations in a cycle work. For example, in a forestry machine, the pressure variation should be considered because the environment is changing. It might cause pressure peaks to the hydraulic cylinder due to stumps and fallen trees.
The most typical hydraulic cylinder configurations
The crucial measurements for all types of cylinders include stroke, bore diameter, and rod diameter. Stroke lengths vary from a few centimeters to several meters. Bore diameters can range from a few centimeters up to more than two meters. Piston rod diameters range from 1,5 centimeters to more than 50 centimeters.
For tie-rod cylinders, increasing the bore's size also means increasing the number of tie rods needed to retain stability. Increasing the bore of the piston rod's diameter is an ideal way to compensate for higher loads. Still, space considerations may not allow this, in which case multiple cylinders may be required.
The tie-rod, welded, and ram cylinder configurations are the most typical styles. Tie-rod cylinders use high-strength threaded steel tie-rods to provide additional stability. Welded cylinders have a barrel welded directly to the end caps. Ram cylinders use a high pressure pushing straight ahead. Ram cylinders are primarily used in heavy-duty applications.
All hydraulic cylinders create linear movement, but different varieties have their unique effects. Below are some of the most common types of hydraulic cylinders.
Single acting hydraulic cylinder
Single-acting cylinders operate only in one direction, so the oil has only one access port into the cylinder. The port is located at the head end of the cylinder, which can only function in one direction. When the oil is pumped into the port, it pushes the rod, causing it to extend'the rod returns for an external force such as the load or a spring. As oil is pushed through, the port is pressed on a plunger and causes the movement. When the cylinder gets empty of oil, the plunger returns itself to the original position.
Advantages for the single-acting cylinders are that they have compact and space-efficient sizes and simple structures. Single-acting cylinders are easy to maintain, reliable in function, and have substantial pressure and force potential. Single-acting cylinders are economical and the most straightforward designs.
Disadvantages for the single-acting cylinders may be that those equipped with retractable springs are vulnerable to component failure as the springs wear out. The wear manifests as a gradual reduction in force on the retracting movement. They are also difficult to seal and can become damaged over time through exposure to corrosive fluids. Single-acting cylinders are primarily used in construction plants, internal combustion engines, reciprocating engines, pumps, hydraulic rams, and jacks.
The single-acting, spring-loaded cylinders function with the internal spring that controls the piston's flow and the single port's fluid. The seals at the head of the piston stop the fluid from reaching the spring. This feature ensures the spring and the fluid can function together in different directions, with additional forces being applied from either side. These cylinders are primarily used to push and pull when required. They can also be mounted vertically to allow the piston's weight to contribute to the cylinder's function.
Single-acting vs. double-acting
Single-acting and double-acting cylinders are the two most commonly used types of hydraulic cylinders. What is the difference between these two types of cylinders? The simple answer is that a double-acting cylinder has both an A and a B Port. Oil enters the cylinder via A port, which pushes the piston down. Oil diverts to port B when the piston's control calls to retract, pushing the piston up. We have also written a blog post about the differences between single-acting and double-acting hydraulic cylinders, you can read it here.
An illustration of a single-acting hydraulic cylinder
An illustration of a double-acting hydraulic cylinder
Double-acting hydraulic cylinders
Unlike the single-acting cylinder, the double-acting cylinder has two ports; one for extending the plunger and another for retracting. These ports are positioned at either end of the cylinder, the head, and the rod. Both ports are used when retracting the rod, as a rod is extended and a port at the head end is simultaneously used.
Double-acting cylinders have a crucial advantage over other types of cylinders. A ram lip's presence allows the rod to be additionally supported within the cylinder throughout the extending and retracting processes.
A double-acting cylinder is capable of pressure being exerted on either side of the piston alternatively. The outward and retraction movements can be achieved without external power sources when the cylinder is under pressure. The pressure can return the piston to its starting position or apply an alternating force on both sides of the cylinder to operate a crankshaft.
The advantages of double-acting cylinders are that they are easily accessible because they are the most commonly used hydraulic cylinders. They are rugged, reliable, and save energy. Double-acting cylinders need fewer hydraulic fluids, have controlled acceleration, and perform well repetitively accurately. Double-acting cylinders have precisely definable stroke measurements and have a massive variety of potential applications.
Double-acting cylinders are used primarily in large-scale engines, like ship motors, industrial furnaces, digging machines, lift shafts and steering mechanisms.
Balanced, double-acting, piston-type cylinder
An extra-long piston with a clevis allows for careful yet precise changes to the cylinder's pressures and balances without interfering or disrupting the cylinder's other parts and mechanisms. This cylinder has a steel ring seal and ports at either end. The configuration of the piston is different, with access at only one end.
Non-differential cylinder
The non-differential cylinder has two ports, similar to the double-acting cylinder. The main difference between these two is that the rod is extending from both ends. It makes the cylinder more stable and can be measured in terms of speed and thrust placed on the rod within the cylinder.
When the flow can move from end to end of the rod, it makes it an unusual cylinder compared to other designs. It is usable in many different ways but challenging to use, for example, in mobile equipment. The seal, piston, and steel ring provide control and stability to manage the conditions inside and balance the forces.
Telescoping, ram-type, actuating cylinder
Telescopic cylinders are designed with a series of steel or aluminum tubes of progressively smaller diameters nested within each other. Telescopic cylinders can be single or double-acting. In general, telescopic cylinders are more expensive than standard cylinders. Most telescopic cylinders are single-acting, and double-acting telescopic cylinders are specially custom designed and manufactured. Telescopic cylinders are multi-stage units of two or more steps.
This type of cylinder is very different from the other designs. It functions in a very compact structure. Rams placed closely alongside each other to form collective cylinder units. These units work together with one or two ports to control the fluid flow. In this design, the rams and the ports are all contained with the cylinder's housing. A substantial advantage of this design is the cylinder's reach when all the rams are extended together.
Tie rod cylinder
Tie rod-style hydraulic cylinders use high-strength threaded steel rods to hold the two end caps to the cylinder barrel. These designs are often used in industrial factory applications. Small-bore cylinders usually have four tie rods, and large bore cylinders may require up to 16 or 20 tie rods to retain the end caps under the forces produced. Tie rod-style cylinders can be completely disassembled for service and repair and are not always customizable.
Welded body cylinder
Welded body cylinders have several advantages compared to tie rod cylinders. Welded cylinders have a narrow body and often a shorter overall length, enabling them to fit better into tight machinery confines.
Welded cylinders function efficiently due to tie rod stretch at high pressures and long strokes. The welded cylinder is customizable, and unique custom features can be easily mounted to this cylinder design. The welded cylinders are the perfect design for multi-stage telescopic cylinders due to their smooth surface.
Welded hydraulic cylinders dominate the mobile hydraulic equipment market. Construction equipment, excavators, bulldozers, road graders are all using welded design cylinders. Also, material handling equipment such as trucks, lift-gates, and telehandlers have welded cylinders. A heavy-duty industry like cranes, oil rigs, and large off-road vehicles for above-ground mining operations are widely using welded cylinders.
Tandem hydraulic cylinder
In a tandem hydraulic cylinder, there are two interconnected cylinders that operate together. This generates a greater force than one cylinder would create on its own. Tandem hydraulic cylinders' general applications include fork lift trucks, elevated work platforms, cranes and barges.
Tandem hydraulic cylinders are used for example in fork lifts. Single-acting hydraulic cylinders only need to create force into once direction
Cushioned Cylinder
The cushioned cylinder is designed with cushioned padding to prevent the piston's stroke from being too strong and stabilizing the cylinder's pressures. The metering device inside the cylinder controls and restricts the piston's power when operating and creates the cushioned effect results.
Differential cylinder
A differential cylinder acts as a standard cylinder when pulling. However, if the cylinder has to push, the oil from the cylinder's piston rod side doesn't return to the reservoir but goes to its bottom. Differential cylinders are manufactured as standard cylinders.
Plunger cylinder
A plunger cylinder is a design without a piston or with a piston without seals. This cylinder can be used only for pushing. The maximum force this cylinder creates is the piston rod area multiplied by pressure. This means that a plunger cylinder has a relatively thick piston rod.
Position sensing intelligent hydraulic cylinder
The intelligent position sensing hydraulic cylinders eliminate the need for a hollow cylinder rod. An external sensing bar senses the cylinder's piston's position by placing a stable magnet within the piston. The magnet spreads a magnetic field through the cylinder's steel wall, providing a sensor locating signal.
Reliable, high-quality custom hydraulics systems are essential to keep your machinery running at peak efficiency. Poorly designed hydraulics systems will lead to higher operational costs and lost income due to downtime. Working with an experienced custom hydraulic specialist is essential.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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:
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.
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