Almost every manufacturing plant in the developed world uses some kind of mechanical motion powered by air, gas or hydraulic fluid. These motions are either linear or rotary. Different types of cylinders, depending on application, generate the linear motions.
In general, cylinders can be classified under one of several headings:
- Piston and rod (standard design).
- Rodless cylinders (mechanically linked to piston).
- Rodless cylinders (magnetically linked to piston).
- Rolling bellows cylinders.
- Variable area rodless cylinders.
- Piston and rod cylinders
These are the most widely used in the industry. They consist of a barrel in which a piston is fitted and from which a rod extends. A double-acting cylinder has a rod extending from both ends. Fluid pressure on either end of the piston causes the extending rod to move back and forth. The piston and rod cylinders are available in barrel diameters from 5/32 in. to 48 in. They feature strokes from 1/4 in. and up.
This design has the advantage of being able to produce high forces within a small package. Depending on the design details, the units can withstand pressures to 15,000 psi. However, the nature of the design dictates a certain minimum pressure needed to move the piston. The cost of operation for cylinders of this design is a function of leakage past the piston and rod seal.
Several system requirements must be met before this type of cylinder can be used:
- The system must be clean.
- The rod and piston must be well guided mechanically.
- There must be minimal side loading.
- The cylinder seals must be suitable for the application.
This variety of unit is designed for limited space applications. Rodless cylinders are powered by compressed air with a maximum pressure of 150 psi. This is why they are not suitable for delivering high forces. The magnetically coupled rodless cylinders have an even smaller load capacity. All rodless cylinders exhibit an inherent leakage.
Other types of cylinders
Rolling bellows cylinders have a characteristically short stroke and are powered by air. They can tolerate some side loading and withstand some level of dirt. In general, the rolling bellows cylinders find limited use. One reason is that this design has a relatively short life cycle.
Variable area cylinders, powered by air or a fluid compatible with rubber, handle pressures to 120 psi. This type of cylinder is very flexible, insensitive to dirty conditions, able to tolerate tremendous side loading, and excellent for shock absorption applications. Although they can bend 10 to 15 degrees, the variable area cylinders provide only a short stroke. They exhibit no leakage and are long lasting.