Single Acting vs Double Acting Pneumatic Cylinders?

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

 

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.