Hydraulic cylinders are used in countless applications. They are often seen at work in both industrial applications (including hydraulic presses, cranes, forges, and packing machines), and mobile applications (such as agricultural machines, construction vehicles, and marine equipment). They’re essential to the operation of excavators, loaders, balers, telehandlers, man-lifts, drill-rigs, and dump trucks—not to mention operating booms, arms, lifts, platforms, and buckets. Hydraulic cylinders are the most effective and efficient method of pushing, pulling, lifting and lowering.
And, when compared with pneumatic, mechanical or electric systems, hydraulics can be simpler, more durable, and offer greater power density. For example, a hydraulic pump has about ten times the power density of an electric motor of similar size. Hydraulic cylinders are also available in an impressive array of scales to meet a wide range of application needs.
Selecting the right cylinder for an application is critical to attaining maximum performance and reliability. That means taking into consideration several parameters. Fortunately, an assortment of cylinder types, mounting techniques and rules of thumb are available to help.
When you’re designing an application that involves hydraulic cylinders, it’s important to consider operating conditions. Cylinders must match a specific application in terms of the amount of pressure, the force exerted, and space requirements imposed by the machinery’s design. But knowing the operating requirements is only half of the challenge. Cylinders must be able to withstand extreme high or low temperatures for some designs. They may be required to handle issues like humidity or salt water for marine hydraulic systems. Wherever temperatures typically rise to more than 300° F, standard Buna-N nitrile rubber seals may fail—so you’ll have to choose cylinders with Viton synthetic rubber seals instead. When in doubt, assume operating conditions will be more rugged than they appear at first glance.
The type of metal 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 steel for heads and bases, which is adequate for most applications. But stronger materials, such as 65-45-12 ductile iron for rod bearings, can provide a sizable performance advantage for tough industrial tasks. The type of piston rod material can be important in wet or high-humidity environments, where 17-4PH stainless steel may be more durable than the standard case-hardened carbon steel with chrome plating used for most piston rods.
Some questions to consider include:
• What is the maximum pressure range for the application?
• Do I need the cylinder to push or pull—or both?
• What push or pull tonnage is required?
• What stroke length will be required?
• What mounting method is being used? and
• How much support will the piston and cylinder require?