Air Cylinders

Every air cylinder is composed of a piston, end covers and a cylinder barrel with at least one air inlet. As compressed air is directed into the cylinder, it pushes the piston along the cylinder's length. The cylinder can be connected to a protruding rod or other structure, which is itself connected to the object that is intended to be moved. There are two categories into which all air cylinders fit. In single acting cylinders, a single inlet allows compressed air in, which moves the piston. A spring behind the piston pushes the piston back when the compressed air is evacuated. In double acting cylinders, two inlets, one on either side of the piston, allow compressed air in and out, pushing the piston back and forth. Valves control the flow of compressed air to the cylinder in both configurations. Other cylinder construction varieties include rotary cylinders, cable cylinders and rodless cylinders, all of which are alternatives to rod-equipped cylinders. Stainless steel and brass are among the most common cylinder construction materials. Compact cylinders, miniature air cylinders and small air cylinders are gaining prominence among manufacturers as microtechnology development operations require access to them; air cylinders are available in sizes as small as 2.5 mm in diameter to 1,000 mm in diameter.

Air cylinders function as actuators in pneumatic systems; an actuator is any mechanism that supplies or transmits controlled energy as part of a mechanical process. Many mechanical processes require access to an actuation method that is reliable, makes no use of harmful chemicals and that is available in many configurations. Different applications call for different air cylinder configurations. The single acting cylinder is able to perform an operating motion in one direction. Pressurized air is introduced on one side of a piston, which causes the piston to move. A spring on the other side of the piston supplies the return force after the pressurized air is released. Single acting cylinders require approximately half the amount of air used by a double acting cylinder for a single operating cycle. A double acting pneumatic cylinder is capable of powered motion in two directions. When a cylinder is pushed out in one direction, compressed air moves it back in the other direction. Air lines running into both ends of the cylinder supply the compressed air. Within these two main configuration categories, there are many specialized configurations available.

Cable cylinders have elongated housing, two rollers and a cable that extends from one end of the cylinder to the other. The yoke, which is the load-bearing surface, is suspended by the cable and moves its attached load as the cable moves back and forth. Rotary cylinders differ from typical air cylinders because they allow revolving motion instead of linear motion. They are typically housed in a circular enclosure in which impellers turn around an axis when pushed by a stream of compressed air. The load-bearing carriage is attached to the axis, which turns in circles both clockwise and counter clockwise. Rodless cylinders are made of long barrels formed with a vertical slot that allow the piston to connect to a load-bearing carriage. They can use mechanical or magnetic coupling to convey force, usually to a body that moves along the length of the cylinder. Each of these configurations varies in size and in load-bearing capacity. The smallest varieties are used in the processing of very small electronics, and the largest are used in heavy-duty industrial processes. A cylinder's composition also depends on its intended application. Stainless steel, for example, is chosen for cylinders that will sustain heavy loads and be subject to harsh conditions.

Choosing an air cylinder for a pneumatic system can be a difficult task. ISO 6432-compliant cylinders all conform to the same dimensions from manufacturer to manufacturer, but not all air cylinder producers make compliant cylinders. If two non-ISO-certified cylinders from different manufacturers are compared, they can have the same bore dimensions, but their stroke length and other dimensions may differ. Because so many of the processes in which air cylinders are used require extreme precision, every air cylinder must be carefully chosen to ensure proper and safe operation. Cylinders should be chosen for their ability to move the greatest load at the lowest acceptable velocity with the minimum available pressure. Cylinder mounting hardware, which includes noses, blocks, pivots and other equipment, is chosen based on the size, force and function of the cylinder. Optional components that help to improve cylinder performance or prevent problems include cushions, bumpers, stop tubes, dual pistons, flow controls, position-sensing switches and position feedback sensors. Carefully chosen air cylinders can be great assets to their users; they are effective, environmentally friendly and available in enough configurations to suit the needs of most industries. 

Types of Air Cylinders

Adjustable stroke cylinders have adjustable stops at one or both ends to restrict the amount of piston travel.

• Brass cylinders are pneumatic actuators built of specific copper alloys that resist corrosion and wear and allow use in a number of harsh industrial environments.

• Cable cylinders are pneumatic devices that utilize pressure differentials to convert compressed air energy into mechanical energy in order to facilitate lateral movement of a cable or wire and all attached loads.Clean profile cylinders are flat barrels with round edges and T-slots for sensors along the entire length of the barrel on three sides. Clean profile cylinders are used in applications that require ease of cleaning and good hygiene as the clean, square line design prevents the collection of dust and dirt.

• Compact cylinders, also called "short stroke cylinders," are cylinders whose overall dimensions at zero stroke are minute compared to the typical cushioned cylinders. These low-profile cylinders are used in applications in which there is not enough space for a standard length cylinder, as they can lock or move short distances, even in limited spaces.

• Compressed air cylinders convert power from compressed air into mechanical power.

• Double acting cylinders have air lines that provide pressure to both ends of the cylinder, supplying motion in two directions. The flow of compressed air is controlled by valves.

• Double rod cylinders have one piston, and the piston rod extends from both ends of the cylinder.

• Miniature air cylinders, also called "microcylinders," are small, rectangular, single-acting air cylinders in which the springs are housed inside enlarged piston rods. Miniature air cylinders operate in reverse motion and are easy to install. They offer a range of interchangeable mounting brackets, which attach to the cylinder ends to provide versatility and adaptability and can be powered by plant air.

• Multiple bore cylinders have two or more boxes and pistons combined or stacked in the same cylinder.

• Multiple-position cylinders are double-acting cylinders that consist of two cylinders with the same diameter. Multiple-position cylinders provide three or more end positions, as opposed to the normal two provided by other double-acting cylinders.

• Non-rotating cylinders are cylinders in which the piston rod, ram or plunger and the relative rotation of the cylinder housing and piston are set.

• Pancake cylinders have shorter lengths and larger diameters than other cylinders. Pneumatic cylinders are comprised of a piston, a lower and upper port and an expansion chamber.

• Reverse single acting air cylinders are similar to single acting air cylinders, but the port is located on the opposite end in order to provide power on the retraction (or "pull") stroke.

• Rectangular cylinders are encased in a rectangular, box-shaped frame.

• Rodless cylinders have a barrel that is formed with a longitudinal slot, permitting the connection of the piston to the mounting carriage. A hardened band pneumatically seals the cylinder, while a second band on the exterior closes the slot and prevents contamination to the interior of the cylinder; a system of slide rails divides the two bands in the pressure-free zone between the two piston seals, which allows movement of the mounting carriage.

• Rotary cylinders are pneumatic actuators that utilize pressure differentials, converting compressed air energy into mechanical energy, which is manipulated to facilitate rotational movement. Single rod cylinders have only one piston, and the piston rod extends from only one end.

• Single acting cylinders have air pressure that supplies motion and force from one side of the piston flange and a spring that provides the return force after pressure release. Single-acting air cylinders utilize about half the amount of compressed air, which is controlled by valves, required by double-acting air cylinders for a single operating motion.

• Small air cylinders are compact pneumatic actuators precision-built to maximize productivity within a limited amount of space. Smooth body cylinders are cylinders in which the cylinder body encases the piston.

•  Stainless steel cylinders are suitable for harsh environments in which they will be rigorously cleaned for hygienic reasons or exposed to corrosive forces. Stainless steel cylinders are often referred to as "throwaway," as they are irreparable, and therefore, the cheapest of all cylinders.

• Tandem cylinders consist of two or more cylinders with linked piston assemblies.

• Tie-rod cylinders are held together by exterior tie rods and are usually in a rectangular bolt pattern.

• Twin rod cylinders consist of a series of twin-cylinder slide units and feature side-by-side twin cylinders in one body and two piston rods connected with a mounting plate. This design guarantees precise guiding compared to a typical cylinder and applies double the force of a cylinder of the same height.