Cylinders allow hydraulic systems to apply linear motion and force without mechanical gears or levers by transferring the pressure from liquid through a piston to the idea of operation.
Hydraulic cylinders are at 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 electric systems, hydraulics can be simpler, more long lasting, and offer greater power. For example, a hydraulic pump has about ten times the energy density of a power motor of comparable size. Hydraulic cylinders are also obtainable in an impressive selection of scales to meet a wide selection of application needs.
Selecting the right cylinder to get an application is critical to attaining maximum functionality and reliability. Which means taking into consideration several parameters. Fortunately, a variety of cylinder types, mounting techniques and “guidelines” are available to help.
Cylinder types
The three many common cylinder configurations are tie-rod, welded and ram styles. Tie-rod cylinders make use of high-strength threaded steel tie-rods, typically on the outside of the cylinder housing, to provide additional balance. Welded cylinders include a heavy-duty welded cylinder casing with a barrel welded right to the finish caps, and require no tie rods. Ram cylinders are just what they sound like-the cylinder pushes straight ahead using high pressure. Ram cylinders are used in heavy-duty applications and more often than not push loads instead of pull.
For all sorts of cylinders, the key measurements include stroke, bore diameter and rod diameter. Stroke lengths vary from less than an in . to several feet or more. Bore diameters can range between an " up to a lot more than 24 in., and piston rod diameters range between 0.5 in. to a lot more than 20 in. Used, however, the decision of stroke, bore and rod dimensions may be tied to environmental or design circumstances. For example, space may be too limited for the perfect stroke length. For tie-rod cylinders, increasing how big is the bore also means increasing the amount of tie rods needed to retain stability. Raising the diameter of the bore or piston rod can be an ideal way to pay for higher loads, but space factors may not enable this, in which particular case multiple cylinders may be required.
Cylinder mounting methods
Mounting strategies also play an important role in cylinder overall performance. Generally, fixed mounts on the centerline of the cylinder are best for straight line push transfer and avoiding use. Common types of mounting include:
Flange mounts-Very strong and rigid, but have small tolerance for misalignment. Specialists recommend cap end mounts for thrust loads and rod end mounts where major loading puts the piston rod in stress.
Side-mounted cylinders-Easy to install and service, however the mounts produce a turning moment as the cylinder applies force to a load, increasing deterioration. In order to avoid this, specify a stroke at least provided that the bore size for aspect mount cylinders (heavy loading can 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 avoid movement in higher pressures or under shock circumstances.
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 little- to medium-bore cylinders.
Key specifications
Operating conditions-Cylinders must match a specific application in terms of the quantity of pressure (psi), force exerted, space requirements imposed by machine design, etc. But knowing the working requirements is only half the challenge. Cylinders must also withstand high temperatures, humidity and actually salt drinking water for marine hydraulic systems. Wherever temperature ranges typically rise to a lot more than 300° F, standard Buna-N nitrile rubber seals may fail-select cylinders with Viton synthetic rubber seals instead. When in question, assume operating conditions will be more rugged 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 might not be adequate to handle 
synthetic liquid hydraulics. Polyurethane is also incompatible with high water-based fluids such as for example water glycol.
Seals -This is just about the most vulnerable aspect of a hydraulic system. Proper seals can reduce friction and put on, lengthening service life, as the wrong kind of seal can result in downtime and maintenance headaches.
Cylinder materials -The type of metal used for cylinder head, base and bearing can make a big hydraulic cylinder change. 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 65-45-12 ductile iron for rod bearings, can provide a sizable performance advantage for tough industrial tasks. The kind of piston rod materials can be essential in wet or high-humidity environments (electronic.g., marine hydraulics) where17-4PH stainless steel may be more durable than the regular case-hardened carbon steel with chrome plating used for most piston rods.