Single Acting vs Double Acting Pneumatic Cylinder

Figure 1: Round pneumatic cylinders: single-acting (left) and double-acting (right)

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Single-acting and double-acting pneumatic cylinders are two of the most common actuators used in industrial applications. Choosing between these cylinder types depends on several factors, including the required force and motion and the specific application requirements. This article explores the key differences between single-acting and double-acting pneumatic cylinders and discusses their advantages, disadvantages, and application-specific suitability.

Table of contents

Pneumatic cylinder operating principle

A pneumatic cylinder converts compressed air energy into linear motion. When compressed air is supplied to one end of the cylinder, the pressure pushes the piston or rod, which performs the mechanical work. A valve regulates compressed air flow into and out of the cylinder, which controls the piston or rod's movement. The efficiency and accuracy of the cylinder's operation depend on the piston and cylinder's size, shape, and material, as well as the pressure and flow rate of the compressed air. Learn more about how pneumatic cylinders operate by reading our pneumatic cylinder overview.

Single-acting pneumatic cylinders

A single-acting pneumatic cylinder operates in one direction. Compressed air enters one side and pushes the piston to the other side. When the air supply shuts off, a spring (Figure 2) or an external force returns the piston to its original position.

Figure 2: A single-acting pneumatic cylinder's working principle: compressed air pushes the piston in one direction, and a compressed spring returns the piston to its original position.

Advantages and disadvantages

Single-acting pneumatic cylinders have the following advantages and disadvantages:

• Advantages
  • Cost: Single-acting cylinders are the cost-effective solution for applications that only require one direction of movement.
  • Air pressure: These cylinders require less air pressure than double-acting pneumatic cylinders.
  • Fail safe: If air pressure is lost due to a malfunction, the spring in the cylinder will automatically return the piston to its original position.
• Disadvantages
  • Control: Although single-acting pneumatic cylinders technically work in both directions, they do not offer the level of control and precision that double-acting cylinders do.
  • Spring issues: The spring mechanism in a single-acting pneumatic cylinder can be prone to failure and it takes up potential work area space.

Applications

• Clamping: Single-acting cylinders are used for clamping applications, where a part or component is held in place. For example, in the woodworking industry, single-acting cylinders hold wood pieces in place while they are being cut or drilled.
• Ejection: In the plastics industry, single-acting cylinders eject finished parts from molds. The compressed air pushes the piston, pushing the finished part out of the mold.
• Lifting: Single-acting pneumatic cylinders can be used for lifting tasks, such as air-powered lifts or vehicle jacks. When compressed air is supplied, it drives the piston upwards, raising the load, and a spring or other external force brings the piston back down to its initial position.

Double-acting pneumatic cylinder

A double-acting pneumatic cylinder operates in both directions, with compressed air applied to both sides of the piston, creating a force in either direction. The air supply pressure to one port pushes the piston towards one side of the cylinder, and reversing the air supply to the other port pushes the piston back to the other side (Figure 3). A 5/3-way pneumatic solenoid valve controls the airflow to each port to move the piston fully in both directions and hold it at an intermediary position.

Figure 3: The working principle of a double-acting pneumatic cylinder. The blue arrows represent the ports receiving the compressed air, pushing the piston away from the port.

Advantages and disadvantages

One of the main advantages of double-acting pneumatic cylinders is their ability to provide a precise and controlled motion in both directions. They are also typically more reliable than single-acting cylinders, as they do not rely on a spring return mechanism. However, double-acting cylinders require more compressed air than single-acting cylinders, and they can be more expensive.

Applications

Double-acting pneumatic cylinders are used in various industrial applications where precise control of motion and force is required. Some common applications include:

• Material Handling: Double-acting cylinders are used in material handling applications, such as conveyor systems or lifting equipment. They provide more precise control of motion and force, allowing for efficient and safe handling of materials.
• Robotics: Double-acting cylinders are commonly used in robotics, where precise and controlled motion is essential. They control the movement of robot arms and other components.
• Machine Tools: Double-acting cylinders are used in machine tools, such as milling machines or lathes. They control cutting tools and other components precisely, allowing for efficient and accurate machining.

Choosing the right pneumatic cylinder

Despite using compressed air as their power source, single-acting and double-acting pneumatic cylinders have distinct performance characteristics due to their different port designs. Single-acting cylinders are mainly used in industrial settings that require force in one direction, such as ejecting parts from conveyor belts. However, double-acting cylinders have superior speed, strength, and efficiency, making them well-suited for applications that demand high force and rapid movement. In summary, single-acting cylinders are suitable for light assembly work. Double-acting cylinders are better suited for applications requiring both speed and force.

FAQs

Which are better, single- or double-acting pneumatic cylinders?

The better choice between single- and double-acting pneumatic cylinders depends on the application. For example, single-acting is more suitable for simple applications that do not require controlled retraction.

What is the difference between single-acting and double-acting pneumatic cylinders?

Single-acting cylinders have one entry port for compressed air, pushing the piston in one direction. Double-acting cylinders have an entry port on each end, allowing the air to control the piston in both directions.

Are you looking for devices to perform continuous movement without the need of pushing buttons? Many business sectors such as factory automation, packaging, transportation and automotive manufacturing implement pneumatic components into their machine designs. Pneumatic systems are known to remain reliable, inexpensive, and clean.

Pneumatic cylinders, also referred to as air cylinders or actuators, are mechanical devices which use compressed air to move a load in a linear path. The most common type of pneumatic actuator includes a piston and rod moving inside a closed cylinder, where the piston performs the desired movement. In pneumatic systems, air is used as the source of energy to operate and complete a given task, in this case, extending and retracting the piston inside a cylinder. 

Read more about Pneumatic Components on our TecTalk blog, &#;Pneumatic Components: An Industrial Guide.&#;

Pneumatic cylinders are commonly applied as two types of pneumatic cylinders: single acting and double acting. The main design difference between both cylinders is the number of ports. Single acting cylinders has one port where pressurized air enters, while double acting cylinders use two ports to operate. This simple design difference distinguishes both cylinders in terms of movement and speed. When choosing a design, it is important to know the application of each device, their differences, advantages and disadvantages.

Single Acting Cylinder

If you are looking to utilize your machine in a linear motion and perform movements such as clamping, positioning and punching, then single acting cylinders might be your solution. How do they work? Single acting cylinders have one port where pressurized air enters in one direction. A spring, or a load, is usually fitted to the piston. Once air is cleaned and compressed it enters through the single port forcing the piston to extend in one direction compressing the spring. The spring (or another external force) will retract the piston back to its original position after releasing air through the same port where it originally entered. Simply put, the compressed air will force a forward stroke inside the cylinder and the spring will return the stroke. 

There are two different types of single acting cylinders, push and pull. 

• Push Type Cylinder: Air enters to push the piston out of the cylinder

   
• Pull Type Cylinder: Air enters to pull the piston inside of the cylinder

Advantages of Single Acting Cylinder:

• Simple design; easy to install

• Low cost of initial purchase 

• Single port and small housing

• Reduction in valve and piping cost compared to double acting cylinders

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Disadvantages of Single Acting Cylinder:

• Compressed air requires proper preparation

• Spring takes too much space and limits working area

• Reduced thrust due to the opposing spring force

• With prolonged spring usage, pistons strokes can become inconsistent

Double Acting Cylinder

When looking for a device to move load in both directions, double acting cylinders are a useful application when your machine requires more than one movement. Unlike single acting air cylinders, double acting cylinders can extend and retract without the need of a spring. Instead of applying pressurized air into one port, double acting cylinders have two ports where air can enter in and out. 

Air enters through one port moving the piston forward and then applies pressurized air into 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 given their ability to extend and retract within a shorter time period, thus, becoming more efficient and precise. 

Double acting pneumatic cylinders are mostly used in industrial and robotics industries. They perform tasks such as opening/closing doors and lifting and moving merchandise off conveyor belts. Other uses include medical applications, earth-moving equipment and space programs. 

 Advantages of Double Acting Cylinder:

• More control over movement since pressurized air moves both ways

• Faster, stronger and use less energy 

• Offer more design variation: stroke and bore sizes

• Many double acting pneumatic cylinders are ISO compliant as opposed to single pneumatic cylinders

Disadvantages of Double Acting Cylinder:

• More costly than single pneumatic cylinders

• Requires bigger housing - if used as a feed cylinder it needs to be coupled with another machine system  

• In certain situations, air consumption may be calculated at different rates 

Single vs Double Acting Cylinders: Which one should I choose?

Although both systems use compressed air as their main source of energy, their port design allows them to perform quite differently.  Single acting cylinders are mainly used in industrial applications where force is needed in one direction, for example, ejecting parts/items off conveyor belts. Double acting cylinders, on the other hand, are widely recognized across many industries for being faster, stronger, and more efficient than single acting cylinders. Applications that require speed and force will need the help of double acting cylinders whereas light assembly work can be deployed by single acting cylinders. 

When choosing the correct style of pneumatic actuator for your system it is crucial to take into consideration budgeting. How often are you able to provide maintenance? Does your system require machines to be running all day? These are a few questions to keep in mind when choosing the right pneumatic cylinder. Since single acting cylinders will require more maintenance than double acting cylinders, their initial purchase cost is much lower. Additionally, single acting cylinders will often need to be replaced. Over time the spring will stretch and cause inaccurate precision. In terms of power, double acting cylinders can perform quicker and stronger when compared to single acting cylinders. Despite of their cost, double acting pneumatic cylinders continue to be widely used and recognized for their superior design.

Additional Notes: Pneumatic cylinders require air to be cleaned and filtered and if not properly prepared your system and products are open to contamination and possible malfunctions. It is also important to consider ISO standards when choosing your pneumatic actuator. While single acting cylinders are considered easier to use and maintain, many double acting cylinders meet ISO standards. 

Do you still have questions regarding which type of cylinder is best for your application? Feel free to contact one of our technical sales reps for assistance.

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