Single-acting Cylinder VS Double-acting Cylinder

Update:22 Jun 2021

Pneumatic cylinders, also referred to as air cylinders […]

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.

Single-acting cylinder

In a single-acting cylinder (SAC), air is only supplied to one side of the piston and is responsible for the movement of the piston in only one direction. The movement of the piston in the opposite direction is performed by a mechanical spring. A single-acting cylinder can be designed to be with base position minus (spring return) or base position plus (spring extend) depending on whether the compressed air performs the out stroke or the in-stroke respectively. In case of pressure or power loss, a single-acting cylinder has the advantage of returning the piston to a base position.

A downside of single-acting cylinders is the inconsistent output force through a full stroke due to the opposing spring force. Furthermore, the stroke of a single-acting cylinder can be limited due to the space the compressed spring takes up and spring length availabilities. The construction length of a single-acting cylinder is therefore longer than its actual stroke.

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.

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