Cylinders allow hydraulic systems to use linear motion and drive without mechanical gears or levers by transferring the pressure from liquid through a piston to the idea of operation.
Hydraulic cylinders are in work in both commercial applications (hydraulic presses, cranes, forges, packing machines), and mobile applications (agricultural machines, construction equipment, marine equipment). And, in comparison to pneumatic, mechanical or electrical systems, hydraulics could be simpler, more long lasting, and provide greater power. For instance, a hydraulic pump has about ten times the energy density of an electric motor of similar size. Hydraulic cylinders are also obtainable in an impressive selection of scales to meet a wide selection of application needs.
Choosing the right cylinder for an application is critical to attaining maximum efficiency and reliability. Which means considering several parameters. Fortunately, an assortment of cylinder types, installation techniques and “rules of thumb” are available to help.
The three many common cylinder configurations are tie-rod, welded and ram styles. Tie-rod cylinders make use of high-strength threaded metal tie-rods, typically externally of the cylinder casing, to provide additional stability. Welded cylinders include a heavy-duty welded cylinder casing with a barrel welded right to the end caps, and require no tie rods. Ram cylinders are simply what they audio like-the cylinder pushes straight ahead using very high pressure. Ram cylinders are used in heavy-duty applications and almost always push loads instead of pull.
For all types of cylinders, the crucial measurements include stroke, bore diameter and rod diameter. Stroke lengths vary from less than an in . to several feet or even more. Bore diameters can range between an inch up to more than 24 in., and piston rod diameters range between 0.5 in. to more than 20 in. In practice, however, the decision of stroke, bore and rod sizes may be limited by environmental or design conditions. For example, space may be too limited for the ideal stroke duration. For tie-rod cylinders, raising the size of the bore does mean increasing the amount of tie rods had a need to retain stability. Increasing the diameter of the bore or piston rod is usually an ideal way to compensate for higher loads, but space factors may not enable this, in which particular case multiple cylinders may be required.
Cylinder mounting methods
Mounting methods also play an important role in cylinder efficiency. Generally, fixed mounts on the hydraulic cylinder centerline of the cylinder are best for straight line push transfer and avoiding put on. Common types of mounting include:
Flange mounts-Very strong and rigid, but possess small tolerance for misalignment. Experts recommend cap end mounts for thrust loads and rod end mounts where major loading places the piston rod in tension.
Side-mounted cylinders-Easy to set up and service, but the mounts create a turning moment as the cylinder applies force to a load, increasing deterioration. To avoid this, specify a stroke at least as long as the bore size for side mount cylinders (weighty loading tends to make short stroke, huge bore cylinders unstable). Side mounts need to be well aligned and the strain supported and guided.
Centerline lug mounts -Absorb forces on the centerline, but require dowel pins to secure the lugs to avoid movement in higher pressures or under shock conditions.
Pivot mounts -Absorb force on the cylinder centerline and let the cylinder modify alignment in a single plane. Common types consist of clevises, trunnion mounts and spherical bearings. Because these mounts allow a cylinder to pivot, they should be used in combination with rod-end attachments that also pivot. Clevis mounts can be utilized in any orientation and are generally recommended for short strokes and little- to medium-bore cylinders.
Operating conditions-Cylinders must match a particular application with regards to the amount of pressure (psi), pressure exerted, space requirements imposed by machine design, and so forth. But knowing the operating requirements is only half the challenge. Cylinders must also withstand high temperatures, humidity and actually salt water for marine hydraulic systems. Wherever temperatures typically rise to more than 300° F, standard Buna-N nitrile rubber seals may fail-choose cylinders with Viton synthetic rubber seals instead. When in question, assume operating conditions will be more tough than they appear initially.
Fluid type-Most hydraulics use a type of mineral oil, but applications involving synthetic liquids, such as phosphate esters, require Viton seals. Once again, Buna-N seals may not be adequate to take care of synthetic fluid hydraulics. Polyurethane is also incompatible with high water-based fluids such as water glycol.
Seals -This is just about the most vulnerable facet of a hydraulic system. Proper seals can decrease friction and use, lengthening service life, as the wrong type of seal can lead to downtime and maintenance nightmares.
Cylinder materials -The type of metal used for cylinder head, base and bearing could make a significant difference. Most cylinders make use of SAE 660 bronze for rod bearings and medium-grade carbon metal for heads and bases, which is sufficient for some applications. But more powerful materials, such as 65-45-12 ductile iron for rod bearings, can provide a sizable performance advantage for challenging industrial tasks. The kind of piston rod material can be important in wet or high-humidity environments (e.g., marine hydraulics) where17-4PH stainless may be stronger than the regular case-hardened carbon metal with chrome plating used for most piston rods.