Although pneumatic cylinders will vary in appearance, size and
function, they generally fall into one of the specific categories shown
below. However there are also numerous other types of pneumatic cylinder
available, many of which are designed to fulfill specific and
specialized functions.
Single-acting cylinders (SAC) use the pressure imparted by compressed
air to create a driving force in one direction (usually out), and a
spring to return to the "home" position. More often than not, this type
of cylinder has limited extension due to the space the compressed spring
takes up. Another downside to SACs is that part of the force produced
by the cylinder is lost as it tries to push against the spring.
Double-acting cylinders (DAC) use the force of air to move in both
extend and retract strokes. They have two ports to allow air in, one for
outstroke and one for instroke. Stroke length for this design is not
limited, however, the piston rod is more vulnerable to buckling and
bending. Additional calculations should be performed as well.
Telescoping cylinders, also known as telescopic cylinders can be either single or double-acting. The telescoping cylinder
incorporates a piston rod nested within a series of hollow stages of
increasing diameter. Upon actuation, the piston rod and each succeeding
stage "telescopes" out as a segmented piston. The main benefit of this
design is the allowance for a notably longer stroke than would be
achieved with a single-stage cylinder of the same collapsed (retracted)
length. One cited drawback to telescoping cylinders is the increased
potential for piston flexion due to the segmented piston design.
Consequently, telescoping cylinders are primarily utilized in
applications where the piston bears minimal side loading.
Although SACs and DACs are the most common types of pneumatic cylinder, the following types are not particularly rare:
Some rodless types have a slot in the wall of the cylinder that is
closed off for much of its length by two flexible metal sealing bands.
The inner one prevents air from escaping, while the outer one protects
the slot and inner band. The piston is actually a pair of them, part of a
comparatively long assembly. They seal to the bore and inner band at
both ends of the assembly. Between the individual pistons, however, are
camming surfaces that "peel off" the bands as the whole sliding assembly
moves toward the sealed volume, and "replace" them as the assembly
moves away from the other end. Between the camming surfaces is part of
the moving assembly that protrudes through the slot to move the load. Of
course, this means that the region where the sealing bands are not in
contact is at atmospheric pressure.
Another type has cables (or a single cable) extending from both (or
one) end[s] of the cylinder. The cables are jacketed in plastic (nylon,
in those referred to), which provides a smooth surface that permits
sealing the cables where they pass through the ends of the cylinder. Of
course, a single cable has to be kept in tension.
Still others have magnets inside the cylinder, part of the piston
assembly, that pull along magnets outside the cylinder wall. The latter
are carried by the actuator that moves the load. The cylinder wall is
thin, to ensure that the inner and outer magnets are near each other.
Multiple modern high-flux magnet groups transmit force without
disengaging or excessive resilience.
https://en.wikipedia.org/wiki/Pneumatic_cylinder
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