Are you looking for equipment that performs continuous motion without having to push a button? Many commercial sectors such as factory automation, packaging, transportation and automotive manufacturing use pneumatic components in their machine designs. Pneumatic systems are known to be reliable, inexpensive and clean.
Pneumatic cylinders, also known as cylinders or actuators, are mechanical devices that use compressed air to move a load in a linear path. The most common type of pneumatic actuator consists of a piston and rod that move inside a closed cylinder where the piston performs the desired motion. In pneumatic systems, air is used as a source of energy to operate and accomplish a given task, in this case extending and retracting the piston within the cylinder.
Cylinders are commonly used as two types of cylinders: single-acting and double-acting. The main design difference between the two cylinders is the number of ports. Single-acting cylinders have one port for compressed air entry, while double-acting cylinders use two ports for operation. This simple design difference distinguishes the two cylinders in terms of motion and speed. When choosing a design, it is important to understand the application of each device, their differences, advantages and disadvantages.
Single acting cylinders
If you want to use your machine in linear motion and perform movements such as clamping, positioning and stamping, then single-acting cylinders may be the solution for you. How do they work? Single-acting cylinders have a port where pressurized air enters from one direction. A spring or load is usually mounted on the piston. Once the air is cleaned and compressed, it enters through the single port, forcing the piston to extend in one direction, which compresses the spring. The spring (or other external force) will retract the piston to its original position after releasing the air through the same port where the piston originally entered. In short, the compressed air will force a forward stroke in the cylinder and the spring will return to the stroke.
There are two different types of single acting cylinders, push and pull.
- Push cylinders: air enters to push the piston out of the cylinder
- Pull-type cylinders: air enters to pull the piston into the cylinder
Advantages of single-acting cylinders:
- Simple design; easy to install
- Low initial purchase cost
- Small, single-ported enclosure
- Reduced valve and piping costs compared to double-acting cylinders
Disadvantages of single-acting cylinders:
- Compressed air requires proper preparation
- Springs take up too much space and restrict the working area
- Thrust is reduced due to opposing spring forces
- Piston stroke becomes inconsistent as the spring is used for a longer period of time
Double Acting Cylinders
When looking for a device that moves loads in two directions, double-acting cylinders are a useful application when your machine requires multiple movements. Unlike single-acting cylinders, double-acting cylinders do not require a spring to extend or retract. Instead of applying pressurized air to one port, double-acting cylinders have two ports where air can move in and out.
Air enters through one port, moving the piston forward, and then pressurized air is applied to the other port, retracting the piston back into the cylinder. Double-acting cylinders are the most widely used pneumatic actuators compared to single-acting cylinders because they are able to extend and retract in a much shorter period of time, thus becoming more efficient and precise.
Double-acting cylinders are mainly used in the industrial and robotics industries. They perform tasks such as opening/closing doors and lifting and moving merchandise from conveyor belts. Other uses include medical applications, earthmoving equipment and the space program.
Advantages of double acting cylinders:
- Better control of movement due to bi-directional movement of pressurized air
- Faster, stronger, less energy consuming
- More design variations available: stroke and bore
- Many double-acting cylinders are ISO-compliant instead of single cylinders
Disadvantages of double acting cylinders:
- More expensive than individual cylinders
- Requires a larger enclosure - if used as a feed cylinder, it needs to be connected to another machine system
- In some cases, air consumption may be calculated at different rates
Single-acting vs. double-acting cylinders: which one should I choose?
Although both systems use compressed air as their primary energy source, their port designs make them very different. Single-acting cylinders are primarily used in industrial applications that require unidirectional force, such as ejecting parts/items from conveyor belts. On the other hand, double-acting cylinders are faster, stronger, and more efficient than single-acting cylinders, making them widely recognized in many industries. Applications that require speed and force will need the help of double-acting cylinders, while light assembly work can be deployed with single-acting cylinders.
When choosing the right type of pneumatic actuator for your system, it is vital to consider budget. How often will you be able to provide maintenance? Does your system require the machine to run all day? These are a few questions to keep in mind when choosing the right cylinder. Because single-acting cylinders require more maintenance than double-acting cylinders, they have a much lower initial purchase cost. In addition, single-acting cylinders usually need to be replaced. Over time, springs can stretch and cause inaccuracies. In terms of power, double-acting cylinders can perform faster and stronger than single-acting cylinders. Despite the high cost, double-acting cylinders continue to be widely used and recognized for their superior design.
Additional Note: Cylinders require clean and filtered air, and if not properly prepared, your system and products can become contaminated and possibly malfunction. It is also important to consider ISO standards when selecting pneumatic actuators. While single-acting cylinders are considered easier to use and maintain, many double-acting cylinders are ISO compliant.