10 Things to Consider When Buying rotating hydraulic cylinder

Feb. 24, 2025

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Twelve Tips for Better Cylinder Selection - Valin Corporation

Here's how to design hydraulic cylinders that improve performance, last longer, and cost less.

Hydraulic cylinders harness fluid pressure and flow to generate linear motion and force, and they work well in both industrial machines, like presses and plastic-molding machines, and in mobile equipment, like excavators and mining trucks. And when compared with pneumatic, mechanical, or electric linear-motion systems, hydraulics can be simpler, more durable, and offer significantly greater power density.

Hydraulic cylinders are available in an impressive array of types and sizes to meet a wide range of application needs. Choosing the right cylinder is critical for maximum performance and reliability. Here are 12 practical tips for selecting, sizing, and operating the best one for a job.

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Selection Considerations

1. Choose the right cylinder type. Two basic hydraulic cylinder designs for industrial applications are tie-rod and welded cylinders.

Tie-rod cylinders use high-strength threaded steel tie rods on the outside of the cylinder housing for additional strength and stability. In the U.S., this is the most common cylinder type. They're used on most general industrial applications, such as plastics machinery and machine tools, although they tend to be limited to 3,000 psi maximum operating pressure. The cylinders are built to NFPA standards, which makes their dimensions and pressure ratings interchangeable with any other cylinder built to that standard.

Welded or mill-type cylinders have a heavy-duty housing with a barrel welded or bolted directly to the end caps and require no tie rods. Designed for higher pressures, to 5,000 psi or greater, they are generally preferred in more rugged applications such as presses, steel mills, and offshore settings with harsh environments and wide temperature swings.

Unlike U.S. OEMs, European manufacturers typically use mill-type cylinders in almost all general industrial applications. (They also use tie-rod cylinders, but generally for lower-pressure tasks up to 160 bar (2,350 psi).) However, due to the design, tie-rod cylinders are less expensive than mill-type cylinders - another reason for widespread use in the U.S.

Also, keep in mind that cylinders are often customized. NFPA cylinder standards dictate dimensions, pressure ratings, type of mountings, and so on - they're standard catalog products. However, engineers designing custom machinery often need to deviate from the standards with special mountings, port sizes, or configurations to suit a particular application. About 60% of the cylinders sold in the U.S. are catalog items, while 40% are modified products with unique requirements.

2. Select the proper mountings. Mounting methods also play an important role in cylinder performance. The cylinder mounting method first depends on whether the cylinder body is stationary or pivots.

For stationary cylinders, fixed mounts on the centerline of the cylinder are usually best for straight-line force transfer and minimal wear. Among the different variations, flange mounts are generally preferred. Loads are centered on the cylinder and opposing forces are equally balanced on rectangular or round flanges. They're strong and rigid but have little tolerance for misalignment. Experts recommend cap-end mounts for thrust loads and rod-end mounts for pull loads.

Centerline lug mounts also absorb force on the centerline but require dowel pins to secure the lugs to prevent movement at higher pressures or under shock conditions.

Side-mounted or foot-mounted cylinders are relatively easy to install and service, but they generate offset loads. The mounts experience a bending moment as the cylinder applies force to a load, potentially increasing wear and tear. Heavy loading tends to make long-stroke, small-bore cylinders unstable.

Side and foot mounts need to be well aligned and on the same plane, and the load supported and guided. Otherwise, induced side loads due to misalignment lead to cylinder wear and seal leaks. Engineers also must be concerned with shear forces on the bolts. Add a dowel or shear pin and keyway behind the feet to prevent the forces from potentially shearing the mounting bolts. If necessary for extra support, add another set of foot mounts in the cylinder midsection in addition to those on the head and cap ends.

3. Select the right pivot mountings when the cylinder body moves. Pivot mounts absorb force on the cylinder centerline and let a cylinder change alignment in one plane. Common types include clevis, trunnion, and spherical-bearing mounts.

Clevis mounts can be used in any orientation and are generally recommended for short strokes and small to medium-bore cylinders. Cylinder engineers prefer clevis mounts with spherical bearings over those with plain bearings because they allow for a bit more misalignment and are, thus, a bit more forgiving. However, if using a spherical bearing on a rear clevis, they also recommend a rod-end attachment that pivots - such as a spherical rod eye. The combination helps compensate for any side loading or potential misalignment.

Trunnion mounts come in head, mid, and rear-mount versions. The mid-trunnion design is likely the most common, as it offers designers a bit more flexibility. They can be specified exactly in the cylinder mid-section or most anywhere toward the front or rear as the application demands. Once specified, however, the mount is not adjustable.

Sizing Considerations

For all types of cylinders, important parameters include stroke, bore diameter, rod diameter, and pressure rating.

4. Piston-rod diameter is critical. Perhaps the most common error in hydraulic design is underspecifying the piston rod, making a cylinder more prone to stress, wear, and failure. Piston-rod diameters can range from 0.5 to more than 20 in., but they must be sized for the available loads. In a push application, it is extremely important to size the rod diameter properly, based on Euler calculations, to avoid rod buckling or bending.

When designing a cylinder to generate a required force, sizing the rod is always the first consideration. From there, work backward and determine the bore size for the available pressure, and so on.

5. Prevent rod bending. In cylinders with long strokes, a fully extended rod can bend under its own weight. Excessive bending leads to wear and damage to seals and bearings. It could even cock the piston inside the bore, which can score and damage the inner surface of the cylinder. Rod deflection should never exceed 1 to 2 mm.

Cylinder rods that are at risk for bending or misalignment require additional support. Depending on the stroke length, a stop tube - which increases the bearing area of the cylinder - may be required to prevent excessive wear and jack-knifing. Engineers might also consider a larger diameter rod, which increases strength. But that also increases weight and may be self-defeating, so do the math carefully. In extreme cases, users may also need to add external mechanical support for the rod, such as a saddle-type bearing.

6. Watch out for impact loads. Stroke length, the distance needed to push or pull a load, can vary from less than an inch to several feet or more. But when the cylinder extends or retracts, ensure that the piston doesn't bottom out and generate impact loads at the end of the stroke. Engineers have several options: Add internal cushions to decelerate the load near the end of stroke; add an external mechanical stop that prevents the cylinder from bottoming out; or use proportional-valve technology to precisely meter flow and safely decelerate the load.

7. Weigh bore diameter versus operating pressure. To produce a given amount of force, engineers can specify large-bore cylinders that operate at low pressures, or vice versa. Generally, systems that operate at higher pressures but with smaller cylinders are more cost-effective. Also, the benefits cascade. Smaller cylinders require less flow and, in turn, smaller pumps, lines, valves and so on. Many installations see an overall cost reduction by moving to higher pressures.

That said, cylinders are rated for both nominal (standard) pressure and test pressure to account for variations. Systems should never exceed the nominal rated design pressure of a cylinder.

8. Add a factor of safety. While design calculations are essential, real-world operations differ from theoretical results. Always assume peak loads will require additional force. The rule of thumb is to choose a cylinder with a tonnage rating of 20% more than required for the load. That compensates for losses like friction from the load, efficiency losses in the hydraulics, actual pressure below the rated system pressure, slip-stick on cylinder seals and bearings, and so on.

Operating Considerations

Cylinder parameters like stroke and force must match machine requirements, but that is only half the challenge. Environmental and operating demands also play a major part in determining a cylinder's ultimate success.

How to choose a hydraulic cylinder? - HPS International

1Type of cylinders

First element to take into account is the type of cylinder. HPS International manufactures and sells 6 types of cylinders for various applications :

Block cylinders (compact) for plastic injections, molding, cosmetics and packaging.
Tie rods for plastic injection, molding and aluminum injection applications.
Round cylinders (ISO, DIN, CNOMO) for plastic injection and molding.
Special cylinders (made to measure, double bore) for plastic injection, molding and die casting.
Auto-locking cylinders for plastic injections, molding, cosmetics and packaging.
Cylinders for foundries for aluminum injection.

Example : Block cylinder
High Speed : Go for the RCVN
Compact : VBL, VBLS, VCR, VXP
With mechanical sensor : VCE
With inductive sensor : VDI
With magnetic sensor : VBM
Cooling : VRE

2Bore

The first essential information to take into account when choosing the size of the bore is the operating pressure.

Knowing the operating pressure you want to use will help you choose the size of the cylinder bore.

The second key information needed to choose the size of the bore is the amount of force required for the application. Here is a quick formula to find the approximate size of the bore in the direction of cylinder extension :

If you are looking for more details, kindly visit rotating hydraulic cylinder.

F = required force (N)
P = operating pressure (bar)
A = Surface of the bore (mm²)
D = bore diameter (mm)
D = &#;4.F / &#;π.&#;p

As a general rule, the resulting bore diameter is rounded to the next standard bore size.

3Rod

Now that you know the minimum size of the hydraulic cylinder bore, you must now choose the ideal rod size. Most HPS cylinders come with several rod options.

The correct rod is chosen based on the necessary stroke length, which has an effect on the buckling resistance of the rod.

When selecting the rods, the smallest rod in the bore should only be used for reduced stroke thrust loads or in reduced pressure applications. The largest rod should be used in cases that depend on its reliability and maximum strength.

If the desired rod diameter is greater than the largest diameter in the bore size of the selected cylinder, it is time to re-examine the cylinder design parameters. It is usually in these situations that the application requires a custom hydraulic cylinder.

4Mounting

The hydraulic cylinders are divided into two types, depending on their mounting style, either a pivot mounting or a straight line mounting. Pivot mounted cylinders are used when a load is to be moved in an arc and includes supports such as a clevis and a trunnion.

Cylinders mounted in a straight line are used when the load is to be moved in a linear direction. It includes a flange support and a back or front foot.

5Seals

A hydraulic cylinder must have the right seals, as they play a vital role in preventing any oil leaks. This, in turn, guarantees a continuous and flawless use of the cylinder. The seal should be selected based on the cylinder's applications, operating environment and the maximum operating pressure it can withstand.
HPS International offers 4 types of seals :

Standard N Nitrile seals, for temperatures from -20 ° to + 80 ° C, an operating speed of 0.5 m / s. Fluids: mineral oil, filtration ISO 19/17/14.
Viton V FPM seals, for temperatures from -20 ° to + 200 ° C, an operating speed of 0.5 m / s. Non-combustible fluids based on Ester Phosphate (HFD-R), ISO filtration 19/17/14.
Glycol G nitrile seals, for temperatures from -20 ° to + 90 ° C, an operating speed of 0.5 m / s. Fluids: Water-Glycol (HFC), ISO filtration 19/17/14.
PTFE P seals in viton / PTFE, for temperatures from -20 ° ... + 240 ° C, an operating speed of 0.5 m / s. Non-combustible fluid based on Ester Phosphate (HFD-R), ISO filtration 19/17/14.

Other elements to consider when choosing a cylinder such as power, operating mode and switches.

6Sensors

HPS International offers 4 types of hydraulic cylinder sensors. The choice depends on the needs and demands of the clients.

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