Cylinders allow hydraulic systems to use 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 in work in both commercial 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 can be simpler, more durable, and offer greater power. For example, a hydraulic pump has about ten times the energy density 
of an electric motor of comparable size. Hydraulic cylinders are also available in an impressive array of scales to fulfill an array of application needs.
Choosing the right cylinder for an application is crucial to attaining maximum efficiency and reliability. That means taking into consideration several parameters. Fortunately, a variety of cylinder types, mounting techniques and “rules of thumb” are available to greatly help.
Cylinder types
The three many common cylinder configurations are tie-rod, welded and ram styles. Tie-rod cylinders use high-strength threaded steel tie-rods, typically on the outside of the cylinder casing, to provide additional stability. Welded cylinders include a heavy-duty welded cylinder casing with a barrel welded directly to the end caps, and require no tie rods. Ram cylinders are just what they sound like-the cylinder pushes directly ahead using very high pressure. Ram cylinders are used 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 ” to several feet or even more. Bore diameters can range between an ” up to 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 sizes may be limited by environmental or design circumstances. For example, space could be too limited for the perfect stroke duration. For tie-rod cylinders, increasing how big is the bore does mean increasing the amount of tie rods had a need to retain balance. Raising the diameter of the bore or piston rod is usually an ideal way to compensate for higher loads, but space considerations may not allow this, in which case multiple cylinders may be required.
Cylinder mounting methods
Mounting strategies also play a significant role in cylinder efficiency. Generally, set mounts on the centerline of the cylinder are best for straight line pressure transfer and avoiding wear. Common types of installation include:
Flange mounts-Very solid and rigid, but possess little tolerance for misalignment. Specialists recommend cap end mounts for thrust loads and rod end mounts where main loading places the piston rod in stress.
Side-mounted cylinders-Easy to set up 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 as long as the bore size for aspect mount cylinders (heavy loading can make short stroke, large bore cylinders unstable). Part 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 allow cylinder change 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 with rod-end attachments that also pivot. Clevis mounts can be utilized in any orientation and tend to be recommended for short strokes and small- to medium-bore cylinders.
Key specifications
Operating conditions-Cylinders must match a specific application when it comes to the quantity of pressure (psi), force exerted, space requirements imposed by machine design, and so forth. But knowing the working requirements is half the challenge. Cylinders must also withstand high temperatures, humidity and also salt drinking water for marine hydraulic systems. Wherever temperature ranges typically rise to a lot more than 300° F, regular Buna-N nitrile rubber seals may fail-select cylinders with Viton synthetic rubber seals rather. When in question, assume operating conditions will be more durable than they appear initially.
Fluid type-Most hydraulics use a kind of mineral essential oil, but applications involving synthetic liquids, such as for example phosphate esters, require Viton seals. Once again, Buna-N seals might not be adequate to handle synthetic fluid hydraulics. Polyurethane can be incompatible with high water-based liquids such as water glycol.
Seals -This is just about the most vulnerable facet of a hydraulic program. Proper seals can reduce friction and use, lengthening service life, as the wrong kind of seal can result in downtime and maintenance headaches.
Cylinder materials -The type of metallic used for cylinder head, base and bearing can make a significant difference. Most cylinders use SAE 660 bronze for rod bearings and medium-grade carbon metal for heads and bases, which is adequate for some applications. But more powerful materials, such as for example 65-45-12 ductile iron for rod bearings, can provide a big performance advantage for difficult industrial tasks. The type of piston rod material can be important in wet or hydraulic cylinder high-humidity environments (e.g., marine hydraulics) where17-4PH stainless may be stronger than the regular case-hardened carbon steel with chrome plating used for some piston rods.