Cylinders allow hydraulic systems to use linear motion and pressure without mechanical gears or levers by transferring the pressure from fluid 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 instance, 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 meet an array of application needs.
Choosing the right cylinder intended for an application is crucial to attaining maximum overall performance and reliability. That means taking into consideration several parameters. Fortunately, a variety of cylinder types, mounting techniques and “rules of thumb” are available to help.
Cylinder types
The three the majority of 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 housing with a barrel welded directly to the finish caps, and require no tie rods. Ram cylinders are simply 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 types of cylinders, the key 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 inch up to more than 24 in., and piston rod diameters range from 0.5 in. to a lot more than 20 in. Used, however, the choice of stroke, bore and rod dimensions may be limited by environmental or design circumstances. For example, space could be too limited for the perfect stroke length. 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 usually an ideal way to compensate for higher loads, but space considerations may not enable this, in which case multiple cylinders may be required.
Cylinder mounting methods
Mounting methods also play an essential role in cylinder efficiency. Generally, fixed 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 have small 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 install and service, however the mounts produce 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 part mount cylinders (heavy loading can make short stroke, large bore cylinders unstable). Part mounts have 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 avoid movement at 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 include 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 tend to be recommended for short strokes and little- to medium-bore cylinders.
Key specifications
Operating conditions-Cylinders must match a specific application with regards to the amount of pressure (psi), drive exerted, space requirements imposed by machine design, and so forth. But knowing the working requirements is only 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-choose cylinders with Viton synthetic rubber seals rather. When in question, assume operating conditions will be more durable than they appear at first glance.
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 system. Proper seals can hydraulic cylinder reduce friction and use, lengthening service life, as the wrong type of seal can lead to downtime and maintenance nightmares.
Cylinder materials -The type of metallic used for cylinder mind, base and bearing can make a big change. 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 kind of piston rod material can be important in wet or high-humidity environments (e.g., marine hydraulics) where17-4PH stainless steel may be stronger than the standard case-hardened carbon steel with chrome plating used for most piston rods.