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Double-Acting Cylinder Pneumatic Controls

Design of a Double-Acting Cylinder

The following graphic shows how a double-acting cylinder is designed and the relevant symbol in accordance with DIN ISO 1219-1.

double-acting-cylinder-design.jpg

(1) Base
(2) Side of piston
(3) Side of piston rod
(4) Cylinder tube
(5) Case
(6) Piston rod
(7) Piston with seal
(8) Primary air inlet/outlet/
(9) Secondary air inlet/outlet

Depending on which of the two air inlets/outlets (8) or (9) are fed with compressed air, the piston either moves out of the cylinder tube or into the cylinder tube. This cylinder type can thus do pneumatic work in both directions.

How the cylinder works?

The following animation demonstrates how a double-action cylinder works.

double-action-cylinder-works.gif

 

If the compressed air flows through the air inlet on the left (primary inlet), the pistons and piston rods move to the right (forward motion), causing the air displaced into the piston rod chamber to escape to secondary side. If the compressed air is supplied to the secondary side (right-hand air inlet), it acts on the piston ring surface and moves the piston and the piston rods to the left (reverse action). In this case, the displaced air exits on the primary side. In this type of cylinder both forward and return actions are used as operating strokes, but each has a different speed depending on the load. In addition, it uses virtually twice as much air as the single-acting cylinder.

There is an additional feature to be considered regarding the type of design shown above. For the forward, extending motion (compressed air fed in on the primary side) the entire surface of the piston AP is available for the effective force, whereas during reverse action the effective surface (compressed air inlet on the secondary side) is reduced by the cross-section of the piston rod (piston ring surface AS). The following graphic illustrates this situation (the effective surfaces are coloured grey).

double-acting-cylinder-design1.jpg

Thus it follows that

double-acting-cylinder-design2.jpg

meaning that the forces coming into play during forward and reverse actions are equal even if an equal amount of compressed air is applied. This is not true for cylinder types of another design (e.g. with end-to-end piston rod).

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