Pneumatic Cylinders
Chapter 3
1
Basic Operation
A cylinder is a device used to produce
linear motion.
It is composed of 2 basic assemblies,
the barrel and head assembly and the
piston and piston head assembly.
As compressed air is applied to the rear
of the piston and the chamber in front of
the piston is open to exhaust.
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Basic Operation
To retract the cylinder, the air on the rear of
the piston is exhausted to atmosphere and
compressed air is applied to the front of the
piston.
The pneumatic cylinder is composed of
several precision machined parts.
Components common to most cylinders
include the barrel, the front and rear head,
the piston, the piston rod and a number of
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seals.
Cylinder Components
The barrel
Is a carefully machined cylindrical tube.
 Usually made of aluminum, brass, or
stainless steal.
 It forms a chamber which contains the air
and provides a surface for the piston
packing to seal against.
 It is closed at each end by heads.
 Each head may also contain provisions for
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mounting the cylinder

Cylinder Components

They are available in two styles: round
head and square head.
The rod bearing
These give support to the piston rod and
guides it during its stroke.
 These are made of bronze, nylon, or other
bearing material and may be pressed into
the head or placed in a replaceable
cartridge.

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Cylinder Components
The rod seal
Prevents air from escaping between the
piston rod and the front head.
 They are usually of o-ring or u-cup design
and are usually made of buna-N rubber.

The rod wiper

Is designed to prevent dirt and foreign
material from entering the cylinder and
damaging the rod bearing and seal
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Cylinder Components
The piston seal is designed to prevent air
from passing between the piston and
barrel.
O-ring seals are the most popular and
are usually standard in round line
cylinders
They come in a variety of materials and
provide a simple, economical means of
sealing the piston to the barrel.
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Cylinder Mounts
Cylinder mounting styles are:

Centerline, foot, or pivot.
Centerline Mounts
Centerline mounts provide the most secure
means of mounting a cylinder.
 With this mount the thrust is on the same
plane as the mount thereby removing
compound forces from the mounting bolts

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Cylinder Mounts

This type of mount is very strong but
requires accurate alignment
Foot mounting
Foot mounted cylinders are rigidly
mounted, but the mounting plane does not
run through the centerline of the cylinder.
 This places compound forces on the
mounting bolts and creates higher stresses
than centerline.

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Cylinder Mounts
Pivot Mounting
Some applications, such as moving a lever,
require a cylinder to move through an arc
as it cycles.
 To move a cylinder through an arc it is
necessary to pivot mount the cylinder.
 The 2 types of pivot mounts are clevis and
the trunnion.

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Cylinder Mounts
Clevis Mount
Is attached to or is an integral part of the
cylinder.
 This gives a pivot point at the rear of the
cylinder.
 Normally a rod clevis is used with a clevis
mount to provide a pivot point at the rod
end.

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Cylinder Mounts
Trunnion Mount
A trunnion can be attached at any point
along the cylinder.
 This allows pivoting from the front or
middle of the cylinder which reduces some
of the side load inherent in pivot mounting.
 A rod clevis is recommended for use with
trunnion mounting.

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Cylinder Types
Cylinders are available in a variety of
types to meet the requirements of the
various situations in which they are
applied.
They fall into 2 major categories:

Single acting and double acting.
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Cylinder Types
Single acting cylinders
A single acting cylinder is any cylinder
which uses air on only one stroke.
 It uses some other means, usually a spring
to move the piston on the other stroke.
 The stroke using air is the working stroke.
 They are usually classified as push type
and pull type.

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Cylinder Types
Push type cylinder
Push type cylinders use air to extend the
piston.
 When this air is exhausted the spring
returns the piston to its retracted position.

Pull type cylinder

A pull type cylinder uses air to retract the
piston and the spring extends the piston
when the air is removed.
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Cylinder Types
Single acting cylinders are often used for
clamping applications and for those
applications where the cylinder must move
to a certain position whenever the air is
removed.
 A typical application would be to open and
close gates in a grain elevator.
 If air pressure is lost the cylinder would
close the gates to prevent loss of grain.

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Cylinder Types
Double Acting Cylinders
Is a cylinder designed to use air to extend
and retract the piston.
 Double acting cylinders are far more
popular than single acting.
 They are available in single rod end and
double rod end, cushioned and noncushioned.

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Cylinder Types
Although double acting cylinders are
designed to use air on both strokes.
They may be used as single acting
cylinder with load weight, counter
weights or external springs to return the
cylinder.
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Cylinder Types
Single Rod End
The single rod end, double acting cylinder
are by far the most popular cylinder in
industry.
 It is used to move parts and levers,
position tools, control product flow,
assemble products, and package goods.
 They are available in cushioned or non
cushioned.

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Cylinder Types
Double Rod End
The double rod end cylinder is a
specialized cylinder which has a piston rod
extending from the piston through each
end of the cylinder.
 It can be used in applications where 2 work
stations are being used alternately.
 This allows one work station to be loaded
and unloaded while the other is being
worked.
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
Cylinder Types

The second common application is where one
end of the cylinder is used to do the intended
work and the other end is used to actuate limit
valves which control the work.
Cushioned Cylinders
Are designed to reduce the speed of the piston
during the last fraction of an inch of the stroke.
 This reduction in speed, when properly applied,
reduces shock and vibration which means less
noise, wear, maintenance.

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Cylinder Types
However they have little effect when
applied to a massive load moving at a
rapid speed.
 In such applications an external means of
cushioning should be used.

Non Rotating Rod Cylinders

Some applications call for cylinders in
which the rod will not rotate inside the
cylinder.
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Cylinder Types
Rodless Cylinders
These cylinders are available for applications
which require long strokes and must operate
in limited spaces.
 A conventional cylinder takes up at least
twice its stroke in linear space.
 A rodless cylinder occupies little more than its
stroke length.
 The 2 types of rodless cylinders available are
cable and the magnetic band cylinder.
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
Cylinder Types
Cable Cylinders
These double acting cylinder consist of a
piston which reciprocates within the barrel
and a flexible cable which is attached to
both sides of the piston and runs out each
end of the cylinder.
 The load is attached to this bracket which
reciprocates opposite piston.

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Cylinder Types
Magnetic Band
This cylinder has a lug mounted to the side
of the piston which projects through a slot
in the extruded aluminum barrel.
 The slot is sealed by two stainless steel
bands, one inside and one outside, held in
place with permanent magnets.
 As the piston moves, the jug separates the
bands between the piston and recloses
them after it has passed through.
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
Cylinder Types
This cylinder has all the features of the
cable cylinder and has eliminated most of
the problems.
 They are available in lengths up to 30 feet
and generate a force up to approximately
440 pounds.

Tandem Cylinders
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