In industries where linear motion is needed to move products in conveyor belts, lift heavy objects or open valves, pneumatic cylinders are commonly used. A pneumatic cylinder converts compressed air energy into reciprocating linear motion. We’ve discussed more about pneumatic cylinders below: parts, types, working principles, and standards.
Types of Pneumatic Cylinders and Working Principle
Before we look at the working principle of a pneumatic cylinder, we first need to understand the two types of pneumatic cylinders. These are the single-acting and the double-acting pneumatic cylinders.
To illustrate the main parts of a pneumatic cylinder, we’ll consider both the double-acting and the single-acting types. For the double-acting pneumatic cylinder, the main parts are the cap-end port, the tie rod, piston, rod-end port, barrel, and piston rod. A single-acting cylinder will have either a cap-end port or a rod-end port since it utilises a mechanical spring for the opposite/secondary motion.
The barrel is often sealed on either side with a head and end cap, and the mechanical spring or compressed air moves the piston and the piston rod. For these two types, the stroke length is determined by how far the piston rod extends in one full stroke.
Single-acting cylinders use compressed air to drive the piston in only one direction and spring for the opposite motion. This makes them ideal for fail-safe applications requiring the piston to be in a specific position in case of a compressed air loss. They also have a base position and do not provide consistent output force throughout the full-piston stroke length, duce to the opposing spring force.
On the other hand, double-acting pneumatic cylinders give complete control of the piston movement. It also offers a longer piston stroke length and consistent output force in an entire stroke. For this reason, they operate at a higher cycling rate and hence use more energy. However, it’s not suitable for applications that require a base position, especially in fail-safe scenarios when there’s a loss in compressed air.
Pneumatic Cylinder Standards
Most pneumatic cylinders, especially for everyday applications, are designed to be interchangeable with parts and products from different manufacturers. This is possible, thanks to the ISO standards that have been widely adopted in the industry. For every pneumatic cylinder you pick, the cylinder bore, mounting dimensions, airports, stroke, and piston rod characteristics will vary depending on the specific standard and use. Below are the three common pneumatic cylinder standards you should be aware of:
The Round ISO 6432 – (8-25 MM)
This is a metric ISO standard that applies to single-rod pneumatic cylinders whose bores fall within the 8mm – 35mm range. Pneumatic cylinders with the ISO 6432 standard have a maximum working pressure of 10 bars; hence they are often referred to as round cylinders or mini-air cylinders.
And while this cylinder standard doesn’t have manual damping adjustment, the metric series of mounting dimensions allow for easy interchangeability of cylinders. The line of cylinders in the ISO 6432 standard is best used in diagnostic instrumentation, automotive, bottling, and laundry equipment.
The Profile ISO 15552 – (32-320 MM)
Single and double rod pneumatic cylinders with working pressure that don’t exceed 10 bar and bore sizes within 32mm – 320mm range fall under the ISO 15552 standard. Besides the bore sizes, the latter establishes metric mounting dimensions, strokes, mounting styles, and piston rod characteristics for cylinders with detachable mountings. This series also features adjustable cushioning designed for perfect dampening. Hence, pneumatic cylinders in this standard are often used to move large loads in industries and production floors. The ISO 15552 standard has also replaced older ones like the ISO 6431 and the VDMA 24562.
The Compact ISO 21287 (20-100 MM)
This standard applies to single rod compact cylinders with bore sizes in the 20mm to 100mm range and a maximum pressure of up to 10 bar. The ISO 21287 standard doesn’t come with adjustable cushioning but instead features rubber bumpers at either end for efficient operations. Cylinders in this series are also super compact and lightweight; hence they are desirable in space-limited applications.
Pneumatic cylinders are an everyday mechanical device that offers much-needed linear motion in several industrial applications. The two types of pneumatic cylinders, single-acting and double-acting, find their unique use cases in specific settings. For instance, single-acting cylinders are often used in fail-safe applications, while double-acting types allow for a longer piston stroke length and are best used where full control of the linear displacement is required.
Depending on where the pneumatic cylinder is used, some additional accessories may be required. A sensor, for example, maybe mounted onto the cylinder to provide an accurate piston position in automated machinery and equipment. Mounting accessories such as pivots, flanges, spherical eye, etc., are also used to couple the piston to the load, among other use cases.
When selecting a pneumatic cylinder, you need to consider the cylinder diameter, stroke length, mounting style, and operating pressure. Other critical aspects to check are the position feedback, connection size, and cushioning. Where possible, seek professional guidance before picking a pneumatic cylinder for your unique applications.