Pneumatic cylinders (or air cylinders) convert the energy in the form of compressed air to the driving force to activate the fixed mechanisms in modern automated machines. They play an important role as the actuator in the equipment, driving and regulating the mechanism or machine, for instance, lifting the load or opening a valve. Similar to the hydraulic cylinder, a pneumatic cylinder is the application of fluid power which uses a pump controlled by valves to convert power from the working fluid, then compressed air in the system to mechanical energy transported to the moving components.
The working principle involves moving the piston to the proper direction in the cylinder barrel. Subsequently, the piston rod connected to the piston disc will transport the power to activate the operations of either rotary or linear motions. The most evident difference between the two activating systems is the medium.
Using air and gas as the medium in the actuator system, pneumatic cylinders are advantageous for applications that require a clean environment, such as the food processing industry, where the leakage of the cylinder fluids may drip out and contaminate the materials, components, and equipment body.
In addition to clean operations, pneumatic cylinders are also quiet and safe, eliminating the need to critically store the fluids and therefore taking less room. Activating the mechanisms in the machines without any contamination and more simple configuration as well as maintenance, the benefits make the air cylinder an increasingly popular solution. It is also suitable for critical industrial manufacturing applications.
The essential components include the cylinder piston, the pump, two ports, piston rod, and the cylinder barrel which are generally made from stainless steel. The ports refer to the extend port and retract port in a double-acting cylinder. More details of different types, including the double-acting type, of the pneumatic cylinder will be discussed later.
The basic work principle is forcing the piston (attached to the piston rod) to advance backward and forward based on the pressure differentials between the two working chambers. The piston will then push the air back to the storage. The motor of the system is the pump, which supplies regulated fluid flows to the parts to drive the cylinder piston and piston rod. Electric pumps, hand pumps, and hydraulic air pumps are common pumps that are used in these actuators. Following is the introduction of individual components:
The steel body of the cylinder is sealed with one end called cylinder head, which the rod extends out from, and another end which is known as the cap. The cylinder barrel is mostly made from honed tubes which are produced by CDS tubes and DOM tubes. Typically, these pneumatic cylinder barrels have smooth inner surfaces and also tight tolerance.
The cylinder piston separates the pressure chambers within the enclosed design. The two chambers are known as the bottom chamber and rod side chamber. The pistons contained in the barrels are mostly produced with grooves to fit the seals and the bearing. The pressure difference of the compressed air between the chambers can lead to either the extension or retraction, moving the ports.
The piston rod is another essential component that is the important connection of the cylinder system and the moving parts of the equipment. Accurately manufactured to be used as a durable and reliable seal, the piston rod should keep any leakage from the system. The component is generally connected with the cylinder piston, extending out from the rod end side. In the structure of a double-acting type air cylinder, the rod extends outward from 2 sides in opposite directions, which are the 2 sides of the cylinder piston.
Pneumatic cylinders can be divided into the single-acting form and the double-acting form. As the name implies, single-acting cylinders use only one port to force the working air into the cylinder, moving the piston to the required position. The single-acting cylinders mostly utilize internal springs or only gravity to return the component back to its original position. The single-acting type is only suitable for applications that only need a single working direction, for instance, lifting up or pressing down.
Double-acting types have two ports at each end, which refer to extend port and retract port. The two ports which allow the gas in for outstroke and instroke can guide the position of the piston after feeding the high pressure in the system from the pump. Though the double-acting type evidently consumes more power to operate, it is more popular to use nowadays since the pneumatic cylinders can move the loads in two directions, different from the single-acting type.
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