Basic of Pneumatic

8/13/2019 Basic of Pneumatic

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COMPARISON OF PNEUMATIC SYSTEM

WITH HYDRUALIC SYSTEM

Liquids exhibit greater inertia than gases. There fore, in hydraulic

systems, the weight of oil is a potential problem when accelerating

and decelerating the actuators and when suddenly opening and closing

the valves. In accordance with Newtons law of motion, the force

required to accelerate oil is many times greater than that required to

accelerate an equal volume of air.

Liquids also exhibit greater viscosity than gases. This results in larger

frictional pressure and power losses.

ince hydraulic systems use a fluid foreign to the atmosphere, they

require reservoirs and a no!lea" system design. #neumatic systems use

air which is exhausted directly bac" into the surrounding environment.

$enerally, pneumatic systems are less expensive than hydraulic

systems.

%ue to compressibility of air, it is impossible to obtain a precise

control of actuator velocities in pneumatic systems. In applications

where the actuator travel is to be smooth and steady against a variable

load, the air exhaust from the actuator is normally metered.


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&hile pneumatic pressures are quite low due to the compressor

design, hydraulic pressures are high. Thus, hydraulics can be used in

high power systems whereas pneumatics are confined to low power

applications.

BASIC PNEUMATIC SYSTEM:

In pneumatic systems, compressors are used to compress and supply

the necessary quantity of air. 'asically a compressor increases the pressure

of a gas by reducing its volume as described by gas laws. #neumatic systems

normally use a centrali(ed air compressor which is considered to be an

infinite air source. This pressuri(ed air can be piped from one source to the

various locations. The air is piped to each circuit though an air filter, to

remove contaminants which mighty harm the pneumatic components such as

valves and cylinders.

The air then flows through a pressure regulator which reduces the

pressure to the desired level for the particular circuit application. ince air is

not a good lubricant, pneumatic systems require a lubricator to in)ect a fine

mist of oil into the air discharged from the pressure regulator. This prevents

the wear of parts in the pneumatic components.


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*ree air in the atmosphere contains varying amounts of moisture. This

moisture can be harmful since it can wash away lubricants and thus cause

excessive wear and corrosion. +ence sir dries are needed to remove this

undesirable moisture. ince pneumatics systems exhaust air directly into the

atmosphere, they are capable of generating excessive noise. Therefore,

mufflers are mounted on the exhaust ports of air valves and actuators to

reduce the noise.

AIR FILTER

The function of a filter is to remove contaminants from air before it

reaches the pneumatic components such as valves and actuators.

The main component of a filter is the filter cartridge, which is mostly

made of sintered brass or bron(e and other materials. They remove

contaminants in the range of to - microns. These elements have a large

ratio of air to filter media and can thus hold a large amount of contamination

on the surface without suffering any pressure loss.

ir flow entering the filter is directed downward with a swirling

motion that force the moisture and the heavier particles to fall down. The

deflector used in the filter element. The remaining finer foreign particles

move along the air and pass through the cartridge where they are arrested.


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t the bottom of the filter bowl, there is an on!off drain valve, which

could be manually opened to drain the accumulated water and the solid

particles.

PRESSURE REGULATOR:

The main function of this valve is to regulate the incoming pressure to

the system so that the desired air pressure is capable of flowing at a steady

condition. The valve has a metallic body with primary and secondary

openings. The pressure regulation is obtained by opening the poppet valve

to a measured amount for achieving the desired pressure level. This is done

by an ad)ustable screw. The ad)usting screw will move the diaphragm

upward and thus will ma"e the poppet to unseat, thereby creating an opening

to allow air to flow from the primary to secondary side.

The opening of the valve and thereby the pressure of air flowing

through it will be directly proportional to the compression of the spring

underneath the diaphragm. Larger the opening, greater the pressure and vice

versa. In many cases, the valve has two vent hole openings through which

the compressor air is let out into the atmosphere in case the secondary

pressure increases to a level not desirable to the system. The spring at the

other side of the poppet acts as a dampening device to stabili(e the pressure.


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PNEUMATIC VALVES:

To control pneumatic actuators, the air energy has to be regulated,

controlled and reversed with a pre!determined sequence. These are done by

pneumatic valves.

Direction Control Vl!e":

%irection control valves are used to direct the flow of the pressurised

fluid in the desired direction. The main functions of these valves are to start,

stop and regulate the direction of air flow and to help in the distribution of

air in the desired line. The different types of direction control valves are

spool type, poppet type, seat type etc.

#$ T%o&%' !l!e:

This is an on!off type of device. This valve is usually provided with

two external flow ports, a supply port and an exhaust port. normally open

two!way valve permits flow in its normal or in its rest position and bloc"s

flow when actuated. The normally closed valve bloc"s flow in its normal

position and permits flow when actuated.


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($ T)ree&%' !l!e

In this, one flow port is connected to either of the other two ports. It

may be used alternatively to pressuri(e one port and exhaust the other port.

These valves can be used as a pilot relay to operate the other valves. These

valves may be used to control single acting cylinders or in pairs to control

double acting cylinders.

*$ Fo+r&%' !l!e:

*our!way valves have two wor"ing ports, a supply port and an

exhaust port. In one position the valve allows air to flow from the supply

source to one of the wor"ing ports. imultaneously air is allowed to flow

from the other wor"ing port to the exhaust. &hen the valve is shifted, the

flow paths are reversed.

,$ Fi!e&%' !l!e:

in certain designs of direction control valves, five ports are preferred

instead of four ports. This permits the use of either dual supply or dual

exhaust. five port version provides the same basic control of flow paths as

a four port version.


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In addition, dual supply ports permit the use of different pressure for

the cylinder movement. %ual exhaust enables easy exhaustion of the valve.

Pne+-tic C)ec. Vl!e:

chec" valve shuts off against reverse flow and opens at a low

crac"ing pressure in the forward direction. /etal body or light weight

plastic body designs with suitable fittings are available.

Flo% Control Vl!e:

flow control valve has a spring loaded dis" which allows a free

flow in one direction and an ad)ustable or controlled flow in the opposite

direction. *low ad)ustment is performed by a tapered brass stem that

controls the flow through the cross hole in the dis".The ad)ustable "nob

contains an unique loc"ing device that consists of a plastic metering "nob

and a thumb latch pawl. The valve bonnet is inscribed with graduation to

serve as a position indicator for the stem. &hen the pawl is in the up

position, it creates a friction loc" on the valve bonnet and the "nob cannot

rotate. &hen the pawl is at 0-1 to the "nob is free to rotate. /ounting in

any position will not affect the operation.


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Pne+-tic S)+ttle Vl!e or /OR0 T'1e Vl!e

The pneumatic shuttle valve automatically selects the higher of the

two input pressures and connects that pressure to the output port while

bloc"ing the lower pressure. This valve has two input ports and one output

port and employs a free floating spool with an open centre action. t one

end of the spools travel, it connects the second input with the output port.

t the other end of its travel, it connects the second input ports, the output

appears. o the 234 type valve delivers an output when one inptut is

present or when both are present.

/AND0 T'1e or T%o&Pre""+re Vl!e

in this valve, an output is produced if both the input signals are fed.

This has two inlets 56 and 78 and one outlet 58. when signals is fed first to

6, the valve spool moves towards 7, closing the air passage from 6 to .

the reverse ta"es place if air is fed first to 7. if air is fed simultaneously to

6 and 7, then spool remains in its acquired position and air may pass to

from both 6 and 7. If different pressures are present, the lower pressure is

switched to outlet .


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2+ic. E3)+"t Vl!e:

'y using a flow control valve in a pneumatic circuit, the actuator

speed is controlled, which means that the speed of the actuator may be

reduced from its normal speed. 'ut this valve is used to induce a higher

speed in a cylinder by allowing the exhaust air to pass through the direction

control valve 5%9:8 from the cylinder, so that the air energy can act

quic"ly.

&hen air is fed to the piston side of the cylinder, the air in the rod end

of the cylinder exhausts to the atmosphere quic"ly by using this valve.

+ere, the air flowing to the cylinder from the %9: will pass to port 2# of

the quic" exhaust valve and from here to the port of the valve and then to

the cylinder. 'ut the return air from the cylinder will exhaust through and

4 to the atmosphere without traveling through the port 2# and thus avoids

the %9:. o the resistance to piston movement is eliminated to some extent

and speed of the cylinder is accelerated proportionally to the amount of

reduced resistance.


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Ti-e Del' Vl!e

The time delay valve consists of an in! built air reservoir, an in!bait

non!return flow control valve and a pilot controlled spring return ;


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PNEUAMTIC ACTUATORS

#neumatic systems ma"e use of actuators 5linear and rotary8 in a

fashion similar to that of hydraulic systems. 'ut these differ very little from

the hydraulic applications because air is used rather than hydraulic oil?

pressures are either low or medium and a lighter construction is encountered.

#neumatic cylinder construction ma"es extensive use of aluminum and other

non!ferrous alloy materials to reduce the weight and corrosive effects of air

and to improve heat transfer capabilities.

Pne+-tic C'lin4er:

The pneumatic power is converted into straight!line reciprocating

motions by pneumatic cylinders. The various industrial applications for

which air cylinders are used can be divided duty!wise into three groups@

light duty, medium duty and heavy duty.ccording to the operating

principle, air cylinders can be classified as follows.

Sin5le ctin5 c'lin4er:

It has a single air inlet line. &hen this line is pressurised, the piston

extends.


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The return movement of the piston is affected by a built A in spring

mounted on the rod side of the piston or by application of an external force

li"e gravity. ingle acting cylinders with a return spring are limited in

stro"e, because the spring force that must be overcome while extending

increases with the stro"e.

The advantage of a single acting cylinder lies in its reduced air

consumption, since air is not wasted while retracting the piston.

Do+6le ctin5 c'lin4er:

The force exerted bye compressed air moves the piston in two

directions in a double acting cylinder. The double acting cylinder produces

less force during retraction, because the piston rods cross!sectional area is

subtracted from the piston area under pressure.

They are used particularly when the piston is required to perform

wor" not only on the advance movement but also on the return movement.

In principle, the stro"e length is unlimited, although buc"ling and bending

must be considered before we select a particular si(e of piston diameter, rod

length and stro"e length.


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A4!nt5e" o7 4o+6le ctin5 c'lin4er o!er "in5le ctin5 c'lin4er$

In a single acting cylinder, the compressed air is fed only on one

side. +ence, this cylinder can produce wor" only in one direction.

'ut the compressed air moves the piston in two directions in a

double acting cylinder, so they perform wor" in both directions.

In a single acting cylinder, the stro"e is limited by the compressed

length of the spring. 'ut in principle, the stro"e length is unlimited

in a double acting cylinder.

&hile the piston moves forward in a single acting cylinder, the air

has to overcome the pressure of the spring and hence some power

is lost before the actual stro"e of the piston starts. 'ut this problem

is not present in a double acting cylinder.

TANDEM CYLINDER:

It consists of two pistons operating in separate sections along the same

axis with a common piston rod. ince the available force is doubled, this

design is useful when larger forces are required, but a single cylinder with a

larger diameter cannot be accommodate.


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THREE POSITION CYLINDER:

It is quite similar to the tandem cylinder, except that the left piston rod

is not connected to the right piston and the left cylinder is shorter than the

right one. &ith the left piston extended, the retraction of the right piston is

limited to an intermediate position which is determined by the ability of the

right piston to retract fully.

THROUGH ROD CYLINDER:

+ere the piston rod extends to both ends of the piston. This will

ensure equal force and speed on both sides of the cylinder.

AD8USTABLE STRO9E CYLINDER:

The cylinder stro"e can be ad)usted by screwing the left hand piston in

or out. 'y using the shortest possible stro"e needed for a given )ob, better

rapid cycling is achieved and air consumption is reduced.


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TELESCOPING CYLINDER:

&hen pressure is applied to the left side, the inner cylinder acts as a

piston and extends. 3nce it reaches the end of its stro"e, the innermost

piston begins to extend. The available stro"e is almost double when

compared to a normal cylinder having the same retracted length.

AIR MOTOR0S:

To generate rotational motion in a pneumatic system, an air motor is

used. ir motors have been found to provide very high rotational speeds,

which sometimes may go up to B-,--- revolutions per minute. ir motors

are available in the mar"et from a very low to a very high "ilowatt rating.

There are air motors manufactured with fractional "ilowatt as low as -.-

"&, while the higher range is up to =-0"&.

TYPES OF MOTOR0S:

ir motors are of various designs. The most common ones are the

piston type motors and the vane type motors.


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PISTON TYPE MOTORS:

#iston type motors may be of axial or radial type design. The

operation of an axial piston air motor is similar to the piston type hydraulic

motor. s pistons reciprocate in sequence, they actuate a wobble plate and

this in turn imparts a rotary motion to the output shaft through a gear train.

xial piston motors are low power =."& motors while radial piston motors

give up to BC"&. 4adial piston motors are low speed motors.

#iston type motors may have four, five or six cylinders. The power

developed by these motors is dependent on the inlet pressure, the number of

pistons, the area of the pistons, the area of the pistons, the stro"e of the

pistons and the speed. The five A cylinder design provides an even torque at

any given operating speed due to the overlap of the five power impulses

occurring in the stro"e revolution. t least two pistons are on the power

stro"e at all times. The smooth overloading of the power flow and the

accurate balancing ma"e these motors vibrate less at all speeds.


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VANE TYPE MOTORS:

:ane type air motors have longitudinal vanes and these vanes fit into

the radial slots in the rotor. %epending upon the design of the vane type

motor, there might be three to ten vanes. The motors may be designed to

give shaft rotation in one direction only.

In this type, air flows parallel to the shaft through the motor body to

the end plates. It travels through both the end plates via a "idney shaped

port. ir enters into the rotor slot and pushes the vane out. ir passes to the

chamber through the drilled holes in the rotor and acts directly on the

exposed portions of the vanes to turn the rotor.

In this type, the air flows through the chambers to rotate the rotor. The

push pins and the leaf springs are used to "eep the vane out.

APPLICATIONS OF AIR MOTORS:

They may be used in con)unction with hydraulic power units, bench

grinders, conveyor belts, agitators and mixers, feeding devices, hoists,

machine feeders, pipe threaders, tool devices, vibrators and many others.


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PNEUMATIC CIRCUITS:

#neumatic circuits are similar to hydraulic circuits. 3ne difference is

that no return lines are used in pneumatic circuits because the exhaust air is

released directly into the atmosphere. This is depicted by a short dashed line

leading from the exhaust port of each valve or by a smaller triangle. lso no

input device is shown because most pneumatic circuits use a centrali(ed

compressor as their source of energy. The input to the circuit is fixed at

some conveniently located manifold which leads directly into the filter

regulator lubricator 5*4L8 unit.

BASIC PNEUMATIC CIRCUIT:

The forward and return motions of the cylinder are controlled by the

air pressure and hence a four way two position direction control valve is

used. &hen the push button of the D


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+owever, to have more versatility, controllability and flexibility in

operation, a pilot control system is preferred. uch systems used for material

handling are described below.

Fet+re":

B. Nut recessed to avoid mushrooming and disfiguration from impact.

=. 9age to guide )aws for fast set up, solid contact and superior safety.

;. T!handle loc"s )aw opening precisely where you set it.

D. Leverage up front for vice!li"e power and no slippage

. 9enter bolt threads designed for less effort to apply high torque.

INDRODUCTION OF PNEUMATIC SYSTEMS :

Lernin5 O6ecti!e: Explain the operating principles of apneumatic system.

Identify operational characteristics and service procedures applicable to

heavy!duty compressors. The wordpneumatics is a derivative of the $ree"

word pneumatic, which means air, wind, or breath. #neumatics can be

defined as that branch of engineering science that pertains to gaseous

pressure and flow.


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s used in this manual, pneumatics is the portion of fluid power in

which compressed air, or other gas, is used to transmit and control power to

actuating mechanisms. This section discusses the basic principles of

pneumatics, characteristics of gases, heavy!duty air compressors, and air

compressor maintenance. It also discusses the ha(ards of pneumatics,

methods of controlling contamination, and safety precautions associated

with compressed gases.

Co-1re""i6ilit' n4 E31n"ion o7 G"e"

$ases can be readily compressed and are assumed to be perfectly

elastic. This combination of properties gives gas the ability to yield to a

force and return promptly to its original condition when the force is

removed. These are the properties of air that is used in pneumatic tires,

tennis balls, and other deformable ob)ects whose shapes are maintained by

compressed air.

9inetic T)eor' o7 G"e"

In an attempt to explain the compressibility of gases, consider the

container shown in figure ;!D0 as containing a gas. t any given time, some

molecules are moving in one direction, some are travelling in other

directions, and some may be in a state of rest.


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The average effect of the molecules bombarding each container wall

corresponds to the pressure of the gas. s more gas is pumped into the

container, more molecules are available to bombard the walls, thus the

pressure in the container increases. Increasing the speed with which the

molecules hit the walls can also increase the gas pressure in a container. If

the temperature of the gas is raised, the molecules move faster, causing an

increase in pressure. 9onsidering the automobile tire can show this. &hen

you ta"e a long drive on a hot day, the pressure in the tires increases and a

tire that appeared to be soft in cool morning temperature may appear normal

at a higher midday temperature.

Bo'le0" L%

&hen the automotive tire is initially inflated, air that normally

occupies a specific volume is compressed into a smaller volume inside the

tire. This increases the pressure on the inside of the tire.


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9harles 'oyle, an English scientist, was among the first to

experiment with the pressure!volume relationship of gas. %uring an

experiment when he compressed a volume of air, he found that the volume

decreased as pressure increased, and by doubling the force exerted on the

air, he could decrease the volume of the air by half 5fig. ;!-8. Temperature

is a dominant factor affecting the physical properties of gases. It is of

particular concern in calculating changes in the state of gases. Therefore,

the experiment must be performed at a constant temperature. The

relationship between pressure and volume is "nown as 'oyleFs law. 'oyleFs

law states when the temperatureof a gas is constant, the volume of an enclosed

gas varies inversely with pressure. 'oyles law assumes conditions of

constant temperature. In actual situations this is rarely the case. Temperature

changes continually and affects the volume of a given mass of gas.

C)rle";" L%

Gacques 9harles, a *rench physicist, provided much of the foundation

for modem "inetic theory of gases. Through experiments, he found that all

gases expand and contract proportionally to the change in absolute

temperature, providing the pressure remains constant.


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The relationship between volume and temperature is "nown as

9harless law. 9harless law states that the volume of a gas is proportional

to its absolutetemperature if constant pressure is maintained.

PNEUMATIC GASES

$ases serve the same purpose in pneumatic systems as liquids serve in

hydraulic systems. Therefore, many of the same qualities that are considered

when selecting a liquid for a hydraulic system must be considered when

selecting a gas for a pneumatic system.


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2+litie":

The ideal fluid medium for a pneumatic system must be a readily

available gas that is nonpoisonous, chemically stable, free from any acids

that can cause corrosion of system components, and nonflammable. It should

be a gas that will not support combustion of other elements. $ases that have

these desired qualities might not have the required lubricating power.

Therefore, lubrication of the components must be arranged by other means.

*or example, some air compressors are provided with a lubricating system,

some components are lubricated upon installation or, in some cases?

lubrication is introduced into the air supply line 5in! line oilers8. Two gases

meeting these qualities and most commonly used in pneumatic systems

are compressed air and nitrogen. ince nitrogen is used very little except in

gas!charged accumulators, we will only discuss compressed air.

Co-1re""e4 Air

9ompressed air is a mixture of all gases contained in the atmosphere.

+owever, in this manual it is referred to as one of the gases used as a fluid

medium for pneumatic systems. The unlimited supply of air and the

ease of


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9ompression ma"es compressed air the most widely used fluid for

pneumatic systems. lthough moisture and solid particles must be removed

from the air, it does not require the extensive distillation or separation

process required in the production of other gases. 9ompressed air has most

of the desired characteristics of a gas for pneumatic systems. It is

nonpoisonous and nonflammable but does contain oxygen, which

supports combustion.

The most undesirable quality of compressed air as a fluid medium

for a pneumatic system is moisture content. The atmosphere contains

varying amounts of moisture in vapor form. 9hanges in the

temperature of compressed air will cause condensation of moisture in the

system. This condensed moisture can be very harmful to the system

and may free(e the line and components during cold weather.

/oisture separators and air dryers are installed in the lines to

minimi(e or eliminate moisture in systems where moisture would deteriorate

system performance. n air compressor provides the supply of compressed

air at the required volume and pressure.


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In most systems the compressor is part of the system with distribution

lines leading from the compressor to the devices to be operated. Their

operating pressure categori(es compressed air systems as follows@ +igh!

pressure 5+#8H;,--- to ,--- phis /edium!pressure 5/#8HBB to B,---

phis Low!pressure 5L#8HB- phis and below

HEAVY-DUTY AIR COMPRESSORS


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9ompressors are used in pneumatic systems to provide requirements

similar to those required by pumps in hydraulic systems. They furnish

compressed air as required to operate the units of the pneumatic systems.

Even though manufactured by different companies, most compressors

are quite similar. They are governed by a pressure control system that can

be ad)usted to compress air to the maximum pressure.

Co-1re""or De"i5n

The compressor unit may be of the reciprocating, rotary, or screw

design. The reciprocating compressor is similar to that of an automotive

engine. They may be air! or liquid! cooled. s the pistons move up and

down, air flows into the cylinder through the inta"e valve. s the piston

moves upward, the inta"e valve closes and traps air in the cylinder.

The trapped air is compressed until it exceeds the pressure within the

collecting manifold, at which time the discharge valve opens and

the compressed air is forced into the air manifold 5fig. ;! B8. The

reciprocating compressor is normally connected to the engine through a

direct coupling or a clutch.

The engine and compressor are separate units. The rotary compressor

has a number of vanes held in captive in slots in the rotor. These vanes slide

in and out of the slots, as the rotor rotates. *igure ;!= shows an end.


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:iew of the vanes in the slots. The rotor revolves about the center of

the shaft that is offset from the center of the pumping casing. 9entrifugal

force acting on the rotating vanes maintains contact between the edge of the

vanes and the pump casing. This feature causes the vanes to slide in and out

of the slots, as the rotor turns.

Notice in figure ;!= the variation in the clearance between the vanes

and the bottom of the slots, as the rotor revolves. The vanes divide the

crescent!shaped space between the offset rotor and the pump casing into

compartments that increase in si(e, and then decrease in si(e, as the rotor


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rotates. *ree air enters each compartment as successive vanes pass

across the air inta"e. This air is carried around in each compartment and is

discharged at a higher pressure due to the decreasing compartment si(e

5volume8 of the moving compartments as they progress from one end to the

other of the crescent!shaped space.

The compressor is lubricated by oil circulating throughout the unit.

ll oil is removed from the air by an oil separator before the compressed air

leaves the service valves.

The screw compressors used in the N9* are direct! drive, two!stage

machines with two precisely matched spiral!grooved rotors 5fig. ;!;8. the

rotors provide positive!displacement internal compression smoothly and

without surging. 3il is in)ected into the compressor unit and mixes directly

with the air, as the rotors turn compressing the air.

T)e oil )" t)ree 1ri-r' 7+nction":

B. s a coolant, it controls the rise in air temperature normally

associated with the heat of compression.


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=. It seals the lea"age paths between the rotors and the stator

and also between the rotors themselves.

;. It acts as lubricating film between the rotors allowing one

rotor to directly drive the other, which is an idler.

fter the air


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B. The engine oil pressure drops below a certain point.

=. The engine coolant rises above a predetermined temperature.

;. The compressor discharge rises above a certain temperature.

D. ny of the protective safety circuits develop a malfunction.

3ther feature that may be observed in the operation of the air

compressors is a governor system whereby the engine speed is reduced when

less than full air delivery is used. n engine and compression control

system prevents excessive buildup in the receiver.


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Mintin con"tnt 1re""+re$

ccumulators that maintain constant pressure are always

weight!loaded types that place a fixed force on the oil in a closed circuit.

&hether the volume of oil changes from lea"age or from heat expansion or

contraction, this accumulator "eeps the same gravity pressure on the system.


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&hile most accumulators can do any of these things, their use in a

system is limited to only one. The ma)or types of accumulators are as

follows@ pneumatic 5gas!loaded8, weight!loaded, and spring!loaded.

PNEUMATIC ACCUMULATORS:

In the pneumatic accumulators. $as and oil occupy the same

container. &hen the oil pressure rises, incoming oil compresses the gas.

&hen oil pressure drops, the gas expands, forcing oil out. In most cases, the

gas is separated from the oil by a piston 5fig. ;!;B8, a bladder 5fig. ;!;=8, or a

diaphragm 5fig. ;!;;8. this prevents mixing of gas and oil, "eeping gas out

of the hydraulic system.

#$#$ Pre""+re n4 Force$

#ressure is force exerted against a specific area 5force per unit area8

expressed in pounds per square inch 5phi8. #ressure can cause an expansion,

or resistance to compression, of a fluid that is being squee(ed. fluid is any

liquid or gas 5vapor8. *orce is anything that tends to produce or modify

5push or pull8 motion and is expressed in

#ounds.


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$Pressure. n example of pressure is the air 5gas8 that fills an automobile

tire. s a tire is inflated, more air is squee(ed into it than it can hold. The air

inside a tire resists the squee(ing by pushing outward on the casing of the

tire. The outward push of the air is pressure.

Equal pressure throughout a confined area is a characteristic of any

pressuri(ed fluid. *or example, in an inflated tire, the outward push of the air

is uniform throughout. If it were not, a tire would be pushed into odd shapes

because of its elasticity.

Pne+-tic Act+tor":

#neumatic actuator receives pressure energy and converts it to

mechanical force and motion. n actuator can be linear or rotary. linear

actuator gives force and motion outputs in a straight line. It is more

commonly called a cylinder but is also referred to as a ram, reciprocating

motor, or linear motor. rotary actuator produces torque and rotating

motion. It is more commonly called a #neumatic motor


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,$ C'lin4er"$ cylinder is a #neumatic actuator that is constructed of a

piston or plunger that operates in a cylindrical housing by the action of

liquid under pressure. *igure D!Bshows the basic parts of a cylinder.

9ylinder housing is a tube in which a plunger 5piston8 operates. In a ram!

type cylinder, a ram actuates a load directly. In a piston cylinder, a piston

rod is connected to a piston to actuate a load.

n end of a cylinder from which a rod or plunger protrudes is a rod

end. The opposite end is a head end. The #neumatic connections are a head!

end port and a rod!end port 5fluid supply8.

a. Sin5le&Actin5 C'lin4er. This cylinder 5*igure D!B8 only has a

head!end port and is operated pneumatically in one direction. &hen oil is

pumped into a port, it pushes on a plunger, thus extending it. To return or

retract a cylinder, oil must be released to a reservoir. plunger returns either

because of the weight of a load or from some mechanical force such as a

spring. In mobile equipment, a reversing directional valve of a single!acting

type controls flow to and from a single!acting cylinder.


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6$ Do+6le&Actin5 C'lin4er. This cylinder 5*igure D!=, page D!=8

must have ports at the head and rod ends. #umping air into the head end

moves a piston to extend a rod while any oil in the rod end is pushed out and

returned to a reservoir. To retract a rod, flow is reversed. 3il from a pump

goes into a rod end, and a head!end port is connected to allow return flow.

The flow direction to and from a double!acting cylinder can be controlled by

a double!acting directional valve or by actuating a control of a reversible

pump.


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c$ Di77erentil C'lin4er$ In a differential cylinder, the areas where

pressure is applied on a piston are not equal. 3n a head end, a full piston

area is available for applying pressure. t a rod end, only an annular area is

available for applying pressure. rods area is not a factor, and what space

it does ta"e up reduces the volume of oil it will hold.

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Basic of Pneumatic