What are Pneumatic Cylinders
Pneumatic cylinders are mechanical devices that convert compressed air energy into back-and-forth or up-and-down linear motion. These devices are commonly used in applications that require reciprocating linear motion, such as in manufacturing plants to open valves, lift heavy objects, etc. Pneumatic cylinders are also used in trucks and cars for braking purposes.
There are two major types of pneumatic cylinders: single-acting and double-acting cylinders. Single-acting cylinders use compressed air for one-way movement and spring for the return motion. A double-acting cylinder, however, uses compressed air for back-and-forth motion.
The two cylinders have several accessories that enhance optimal operations in different settings. For instance, sensors that detect the piston positioning and mounting accessories allow the addition of other components/loads onto the piston.
Pneumatic Cylinder Parts and Working Principle
Before we look at the working principle of the two types of pneumatic cylinders, we’ll first need to understand the different cylinder parts.
A double-acting cylinder will have all the parts shown above, while the single-acting type will only have a rod-end port or a cap-end rod. The cylinder barrel is always sealed with an end cap and a head cap on the two ends. The general working principle of a pneumatic cylinder is that the compressed air or the spring is designed to move the piston, which in turn drives the piston rod.
Pneumatic cylinders have varying stroke lengths determined by how far the piston rod can extend in every back-and-forth motion. Below is a detailed overview of how the single-acting and double-acting pneumatic cylinders differ.
Double-acting Pneumatic Cylinder
This type is commonly used since it gives complete control of the piston movement. During operation, the piston rod either retracts or extends. When compressed air enters the rod-end port, the rod is retracted (i.e., it’s in a negative position) and, in return, forces the air out of the cap-end port. However, when compressed air enters the cap-end port, the piston moves forward (positive position), extending the piston.
Double-acting cylinders give a longer piston stroke length, full control, and constant output force in every stroke. They also operate at a higher cycling rate. However, they aren’t suitable for applications that require a base position, especially during fail-safe scenarios. This is because the piston will get stuck when compressed air is lost.
Single-Acting Pneumatic Cylinder
As stated earlier, this cylinder uses compressed air to move the piston in one direction, with a mechanical spring used in the opposite motion. Here, the spring is used to either extend or retract the piston. Single-acting cylinder types are suitable for fail-safe applications since the piston always has a base position in case of compressed air loss.
Due to its design, single-acting cylinders do not provide consistent output force. The stroke is also limited due to the space taken by the mechanical spring. Hence, its construction is often longer than the actual stroke length.
Pneumatic Cylinder Standards
Pneumatic cylinders follow some ISO standards that allow them to be used interchangeably with parts and products from different manufacturers. However, some special-application cylinders may not adhere to these design standards. The most common cylinder standards are:
- Round ISO-6432 (8-25 MM) – this ISO standard applies to single-rod cylinders with a maximum working pressure of up to 10 bars or 1000 k Pa and bore sizes from 8mm – 25mm. Cylinders in this standard line are commonly used in automotive, diagnostic instrumentation devices, laundry, and commercial kitchen equipment.
- Profile ISO-15552 (32-320MM) – this standard applies to cylinders with bore sizes from 32mm to 320mm, and maximum working pressure (MAWP) of up to 10 bar or 1000 kPa. These cylinders have adjustable cushioning to help provide the necessary damping; hence they are ideal for operating large loads. They are commonly used in machines running in the construction, beverage, and food industries.
- Compact ISO-21287 (20-100MM) – this standard applies to cylinders with bore sizes from 20mm – 100mm and a MAWP of up to 10 bar. The cylinders do not feature adjustable cushioning; however, they have rubber bumpers at the two ends. They are also lightweight and compact and are commonly used in space-limited applications.
Pneumatic Cylinder Selection Criteria
When choosing a pneumatic cylinder, you should pay attention to factors such as stroke length, cylinder diameter, operating pressure, and mounting style. The diameter of the cylinder is directly proportional to the force it generates from the compressed air. For single-acting types, the spring force should also be considered. Other aspects to consider are cushioning connection size and position feedback.
Summary
Pneumatic cylinders are the everyday mechanical devices used in several industries to provide reciprocating linear motion to drive machines, open doors, valves, etc. These cylinders are available in two main types: single-acting and double-acting. Both types can accommodate different mounting styles (flanges, picots, food mounted, etc.) and accessories (sensors, pneumatic grippers, etc.) depending on the cylinder’s ISO standard. These accessories also impact the system’s reliability, performance, and overall design.
This post is sponsored and written by Maria Schmidt from Tameson
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