Cylinders allow hydraulic systems to apply 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 cellular 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 example, a hydraulic pump offers about ten times the power density of a power motor of similar size. Hydraulic cylinders are also obtainable in an impressive selection of scales to satisfy a wide variety of application needs.
Selecting the right cylinder meant for an application is critical to attaining maximum functionality and reliability. Which means considering several parameters. Fortunately, an assortment of cylinder types, installation techniques and “guidelines” are available to greatly help.
The three most 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 housing, to provide additional balance. Welded cylinders feature a heavy-duty welded cylinder casing with a barrel welded right to the end caps, and need no tie rods. Ram cylinders are just what they audio like-the cylinder pushes straight ahead using high pressure. Ram cylinders are found in heavy-duty applications and more often than not push loads rather than pull.
For all sorts of cylinders, the crucial measurements include stroke, bore diameter and rod diameter. Stroke lengths change from less than an inch to several feet or more. Bore diameters can range from an in . up to a lot 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 measurements may be tied to environmental or design conditions. For example, space may be as well limited for the ideal stroke size. For tie-rod cylinders, increasing the size of the bore does mean increasing the number of tie rods needed to retain stability. Increasing the diameter of the bore or piston rod is certainly an ideal way to pay for higher loads, but space factors may not allow this, in which particular case multiple cylinders could be required.
Cylinder mounting methods
Mounting strategies also play an important role in cylinder performance. Generally, set mounts on the centerline of the cylinder are best for straight line power transfer and avoiding put on. Common types of mounting include:
Flange mounts-Very solid and rigid, but possess little tolerance for misalignment. Professionals recommend cap end mounts for thrust loads and rod end mounts where major loading puts the piston rod in pressure.
Side-mounted cylinders-Easy to set up and service, but the mounts create a turning moment as the cylinder applies force to lots, increasing wear and tear. In order to avoid this, specify a stroke at least so long as the bore size for side mount cylinders (large loading tends to make short stroke, huge bore cylinders unstable). Aspect 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 prevent movement in higher pressures or under shock conditions.
Pivot mounts -Absorb force on the cylinder centerline and let the cylinder alter alignment in one 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 brief strokes and small- to medium-bore cylinders.
Operating conditions-Cylinders must match a particular application in terms of the quantity of pressure (psi), push exerted, space requirements imposed by machine design, etc. But knowing the operating requirements is half the task. Cylinders must withstand high temps, humidity and even salt water for marine hydraulic systems. Wherever temps typically rise to more than 300° F, standard Buna-N nitrile rubber seals may fail-select cylinders with Viton synthetic rubber seals instead. When in doubt, assume operating conditions could be more rugged than they appear initially.
Fluid type-Most hydraulics use a form of mineral oil, but applications involving synthetic fluids, such as phosphate esters, require Viton seals. Once more, Buna-N seals may not be adequate to take care of synthetic liquid hydraulics. Polyurethane is also incompatible with high water-based fluids such as for example water glycol.
Seals -This is probably the most vulnerable aspect of a hydraulic program. Proper seals can decrease hydraulic cylinder friction and wear, lengthening service life, while the wrong kind of seal can result in downtime and maintenance headaches.
Cylinder materials -The kind of steel 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 steel for heads and bases, which is sufficient for most applications. But stronger materials, such as 65-45-12 ductile iron for rod bearings, can offer a sizable performance advantage for challenging industrial tasks. The type of piston rod materials can be essential in wet or high-humidity environments (electronic.g., marine hydraulics) where17-4PH stainless may be more durable than the regular case-hardened carbon metal with chrome plating utilized for some piston rods.