Cylinders allow hydraulic systems to use linear motion and power without mechanical gears or levers by transferring the pressure from liquid through a piston to the point of operation.
Hydraulic cylinders are at work in both industrial applications (hydraulic presses, cranes, forges, packing machines), and mobile applications (agricultural machines, construction equipment, marine equipment). And, when compared with pneumatic, mechanical or electric systems, hydraulics could be simpler, more long lasting, and provide greater power. For instance, a hydraulic pump has about ten times the power density of an electric motor of comparable size. Hydraulic cylinders are also obtainable in an impressive selection of scales to satisfy an array of application needs.
Choosing the right cylinder designed for an application is critical to attaining maximum overall performance and reliability. Which means taking into consideration 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 use high-strength threaded metal tie-rods, typically on the outside of the cylinder housing, to provide additional balance. Welded cylinders feature a heavy-duty welded cylinder casing with a barrel welded right to the finish caps, and need no tie rods. Ram cylinders are just what they audio like-the cylinder pushes straight ahead using very high pressure. Ram cylinders are found in heavy-duty applications and almost always push loads instead of pull.
For all sorts of cylinders, the crucial measurements include stroke, bore diameter and rod diameter. Stroke lengths vary from less than an inch 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 choice of stroke, bore and rod dimensions may be tied to environmental or design circumstances. For example, space may be as well limited for the ideal stroke size. For tie-rod cylinders, raising how big is the bore also means increasing the amount of tie rods had a need to retain balance. Raising the diameter of the bore or piston rod is an ideal way to pay for higher loads, but space considerations may not enable this, in which particular case multiple cylinders may be required.
Cylinder mounting methods
Mounting strategies also play a significant role in cylinder overall performance. Generally, set mounts on the centerline of the cylinder are greatest for straight line pressure transfer and avoiding wear. Common types of installation 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 puts the piston rod in tension.
Side-mounted cylinders-Easy to install and service, but the mounts produce a turning moment as the cylinder applies force to lots, increasing wear and tear. In order to avoid this, specify a stroke at least as long as the bore size for aspect mount cylinders (heavy loading can make short stroke, large bore cylinders unstable). Side mounts need to be well aligned and the load supported and guided.
Centerline lug mounts -Absorb forces on the centerline, but require dowel pins to secure the lugs to prevent movement in higher pressures or under shock circumstances.
Pivot mounts -Absorb force on the cylinder centerline and let the cylinder change alignment in one plane. Common types hydraulic cylinder consist of clevises, trunnion mounts and spherical bearings. Because these mounts enable a cylinder to pivot, they must be used with rod-end attachments that also pivot. Clevis mounts can be used in any orientation and are generally recommended for short strokes and little- to medium-bore cylinders.
Operating conditions-Cylinders must match a particular application when it comes to the amount of pressure (psi), force exerted, space requirements imposed by machine design, and so forth. But knowing the operating requirements is only half the task. Cylinders must withstand high temperatures, humidity and actually salt drinking water for marine hydraulic systems. Wherever temperature ranges typically rise to more than 300° F, standard Buna-N nitrile rubber seals may fail-choose cylinders with Viton synthetic rubber seals rather. When in doubt, assume operating conditions could be more durable than they appear initially.
Fluid type-Most hydraulics use a form of mineral essential oil, but applications involving synthetic fluids, such as phosphate esters, require Viton seals. Once more, Buna-N seals may not be adequate to handle synthetic fluid hydraulics. Polyurethane is also incompatible with high water-based liquids such as for example water glycol.
Seals -This is probably the most vulnerable facet of a hydraulic program. Proper seals can reduce friction and use, lengthening service life, while the wrong kind of seal can lead to downtime and maintenance headaches.
Cylinder materials -The type of metal used for cylinder mind, base and bearing can make a significant difference. Most cylinders make use of SAE 660 bronze for rod bearings and medium-grade carbon steel for heads and bases, which is sufficient for some applications. But more powerful materials, such as for example 65-45-12 ductile iron for rod bearings, can provide a sizable performance advantage for hard industrial tasks. The kind of piston rod materials can be important in wet or high-humidity environments (electronic.g., marine hydraulics) where17-4PH stainless steel may be stronger than the standard case-hardened carbon metal with chrome plating utilized for most piston rods.