Depending on working medium cylinders can be classified as:
PNEUMATIC CYLINDERS
APPLICATIONS OF CYLINDERS
1. Hydraulic Cylinders
2. Pneumatic Cylinders
HYDRAULIC CYLINDERS
Hydraulic cylinders are linear hydraulic motors that turn the hydrostatic power of a fluid into mechanical power. The hydraulic fluid utilized in the cylinder is oil, most commonly used in industrial applications. Hydraulic cylinders consist of a plunger or piston inside a cylindrical housing. The bore of the cylinder must be perfectly cylindrical to prevent any obstruction of the piston. Piston seals prevent internal leakage from the high-pressure side of the hydraulic cylinder to the low side. Rod seals are used to prevent external leakage. Piston rods, which move in and out of the cylinder, are usually hard chrome plated to provide protection from corrosion and wear resistance. Most hydraulic cylinders are made out of steel, stainless steel, or aluminum.
Hydraulic cylinders can be single acting or double acting. A singleacting hydraulic cylinder is configured for motion in only one direction, either pulling in or pushing out. An internal spring is used to provide plunger return when the hydraulic pressure is removed. In single-action hydraulic cylinders, less valving and plumbing is needed than in double-acting cylinders. The more complex double-acting cylinder is pressurized to move in both directions along the vertical or horizontal plane or any other plane as needed. These cylinders provide higher speed operations and tighter control than single-acting cylinders and are less sensitive to system backpressures that can occur due to long tube lengths. A typical hydraulic double-acting cylinder along with all the parts is shown in Figure 6.17 and the part list is
given in Table 6.1.
PNEUMATIC CYLINDERS
Pneumatic cylinders are the final component in a pneumatic or compressed air control or power system. Air or pneumatic cylinders are
devices that convert compressed air power into mechanical energy. This mechanical energy produces linear or rotary motion. In this way, the air cylinder functions as the actuator in the pneumatic system, so it is also known as a pneumatic linear actuator. Main components of a pneumatic cylinder consist of steel or stainless steel piston, a piston rod, a cylinder barrel, and end covers. Pneumatic cylinders can be used for pressure ranges between 5 bars and 20 bars. Consequently they are constructed from lighter materials such as aluminum and brass. Because gas is a compressible substance, the motion of a pneumatic cylinder is hard to control precisely. The basic theory of hydraulic and pneumatic cylinders is otherwise the same. Pneumatic cylinders are a proven way to provide quick, clean, reliable, and
inexpensive linear motion, and a multitude of available designs, styles, and options can suit most any conceivable application. In Figure 6.18, a typical pneumatic double-acting cylinder is shown along with its all the parts. The assembly parts list is given in Table 6.2.
Cylinders found their applications in food processing equipment, chemical and pharmaceutical machinery, power plants, waste-to-steam generating plants, valve actuators, marine use in dams and pollution control, printing machinery, medical and surgical tables, packaging machinery,
damper controls, earth moving machinery, mining industry, construction machinery, plant engineering, defense technology, automotive engineering, mechanical engineering, textile industries, railways, power plants,agricultural machinery, etc.