How Does a Single Action Air Cylinder Work?
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How an Air Cylinder Works
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An air cylinder, or air actuator, is a way to use compressed air to provide a push or pull movement. An air cylinder consists, as the name suggests, of a cylinder, a plunger and an arm. The plunger is sized to fit the cylinder exactly, creating an airtight seal. There are two types of cylinder: single-acting cylinders and double-acting cylinders. In a single-acting cylinder, there is a port at one end and an exhaust at the other. In a double-acting cylinder, there is a port at each end.
The push or pull action is achieved when compressed air is channeled into one of the cylinder ports. The air expands and fills the cylinder, pushing the plunger until it reaches the other end. The force that a cylinder can lift is determined by the air pressure the compressor is producing in PSI (pounds per square inch) multiplied by the area of the plunger. A larger cylinder with a large plunger can lift more than a smaller cylinder at the same air pressure.
Single-acting versus Double-acting
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The difference between a single-acting and a double-acting cylinder is where the compressed air is applied. In a single-acting cylinder, air is applied to only one end of the cylinder to create a push or a pull. Typically, a single-acting cylinder has a spring that returns it to a position, either extended or contracted. Some single-acting cylinders also rely on gravity to return them to their starting position.
A double-acting cylinder has air powering both the extend and contract actions of the cylinder. Compressed air is applied to one end and the other end is exhausted. To reverse the movement, air is applied to the other port and the original port is exhausted.
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Using Double-acting Cylinders as Single-acting
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A factory-designed single-acting cylinder can be used only as a single-acting cylinder. This is because the exhaust on the non-plumbed end is just a small hole, not a threaded port. However, a double-acting cylinder can be used in a single-acting application, provided that no spring return is required. In this sort of application, only one end of the cylinder is plumbed for air and the other is exhausted to atmosphere. This becomes a desirable option to have when you want the cylinder to operate quietly. Exhausting air, which is quite loud, can be plumbed away to an area out of earshot.
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