PNEUMATICS Student Cop

Pneumatics Technology

PNEUMATICS It is a branch of physics that deals with the study of gases especially air, its mechanical properties and applications at pressures higher (compressed) or lower (vacuum) than the atmospheric pressure. It comes from the “Pneuma” meaning breath.

Greek

word

It is the industrial implementation and application of air powered actuators (cylinders and motors) and their control devices (valves) needed in their operations. Recall: Pressure = Force / Area ; Newton / meter 2 = Pascal Pneumatic pressures = 4 to 6 Bars (normal) = 10 Bars (maximum) Force < 3 tons for Pneumatics Force > 3 tons for Hydraulics Conversions: 1 Bar 100 kPa = 14.5 psi 1 Atmospheric Pressure = 1.01325 Bar = 14.7 psi

Another significant advance was the invention of the pneumatic railroad air brake by the American inventor, engineer, and industrialist George Westinghouse about 1868.

APPLICATIONS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Transportation Feeder Supply Positioning Clamping Turning Stamping Bending Hole boring Handling Assembly Measuring Service life testing

DESIGN AND STRUCTURE OF A PNEUMATIC CONTROL Pneumatic controls are designed and represented in the form of control loops. The two basic forms of representation or basic functional groups for pneumatic controls are: 1. 2.

Signal-flow representation Energy flow representation

HISTORY The earliest pneumatic transmission dates from 1700, when the French physicist Denis Papin used power from a waterwheel to compress air that was transmitted through tubes. About a century later the British inventor George Medhurst received a patent to use compressed air to drive a motor, although credit for the first practical application was given to the British inventor George Law, who in 1865 devised the rock drill, in which an airdriven piston operated a hammer tool. The rock drill was widely adopted and used in the drilling of the Mont Cenis railroad tunnel in the Swiss Alps, which opened in 1871, and for the Hoosac tunnel in western Massachusetts, which opened in 1875.

1

SIGNAL OUTPUT Actuator Engineering

SIGNAL PROCESSING Processor Techniques

SIGNAL INPUT Sensory Analysis

Signal-Flow Diagram

Pneumatics Technology ACTUATOR Cylinder

2

DRIVE ELEMENT

Cylinder

SENSOR Push-button

CONTROL ELEMENT

SIGNALING ELEMENT PROCESSOR Directional Control Valve

Directional Control Valve

Push-button

Pressure Line

Pilot Line

Practical Signal-Flow Pneumatic Setup

Air Compressor Electric Motor Practical Energy-Flow Pneumatic Pneumatic Setup ENERGY CONVERSION

Drive Element

Pneumatic / Mechanical



Compressed air is generated and conditioned in a central compressed-air unit and is then distributed in the installation through the compressed-air network.

MACHINE, INSTALLATION Energy Transfer Controlling Element

Actuator Output

ENERGY CONTROL

Drive Elements Cylinders Rotary actuators Pneumatic Compressed-Air Motors Sub-assemblies    

Signal Input Energy Transfer

Signaling Element

Actuators, Controlling Elements and Signaling Elements Directional-control Directional-control valves Flow-control valves Check valves Mechanical / Pressure-control valves Pneumatic  

ENERGY CONVERSION

 

Air-service Units Filters Regulators Lubricators   

CONTROL ENERGY ( Pneumatic or Electrical )

WORKING ENERGY ENERGY ( Electrical )

CENTRAL COMPRESSED-AIR UNIT 

Energy- Flow Diagram

  

Drive assembly and Compressor Reservoir Compressed-air Drier and Cooler Conditioning equipment

Pneumatics Technology ACTUATOR Cylinder

2

DRIVE ELEMENT

Cylinder

SENSOR Push-button

CONTROL ELEMENT

SIGNALING ELEMENT PROCESSOR Directional Control Valve

Directional Control Valve

Push-button

Pressure Line

Pilot Line

Practical Signal-Flow Pneumatic Setup

Air Compressor Electric Motor Practical Energy-Flow Pneumatic Pneumatic Setup ENERGY CONVERSION

Drive Element

Pneumatic / Mechanical



Compressed air is generated and conditioned in a central compressed-air unit and is then distributed in the installation through the compressed-air network.

MACHINE, INSTALLATION Energy Transfer Controlling Element

Actuator Output

ENERGY CONTROL

Drive Elements Cylinders Rotary actuators Pneumatic Compressed-Air Motors Sub-assemblies    

Signal Input Energy Transfer

Signaling Element

Actuators, Controlling Elements and Signaling Elements Directional-control Directional-control valves Flow-control valves Check valves Mechanical / Pressure-control valves Pneumatic  

ENERGY CONVERSION

 

Air-service Units Filters Regulators Lubricators   

CONTROL ENERGY ( Pneumatic or Electrical )

WORKING ENERGY ENERGY ( Electrical )

CENTRAL COMPRESSED-AIR UNIT 

Energy- Flow Diagram

  

Drive assembly and Compressor Reservoir Compressed-air Drier and Cooler Conditioning equipment


PNEUMATIC POWER SUPPLY Pneumatic systems are powered with compressed air. The source of compressed air is the central compressed-air unit also known as pneumatic power supply. The main devices included in the pneumatic power supply are: Compressor(s) Suction Filter Check Valve Cooler Filter with water trap Reservoir Pressure switch Pressure relief valve Pressure gauges Thermometers Hand-slide valve   

3

Flow-type compressors convert the kinetic energy of flowing air into pressure energy. Diaphragm-type compressors are suitable for small-size installations and applications and they deliver oil-free air.

Suction Filter

Compressor head, first stage

highly mobile

Compressor head, second stage

       

COMPRESSOR The device that generates compressed air is the compressor. It converts mechanical energy to pneumatic energy of the compressed air. Different types of compressors are known, depending on their construction, as follows: Piston compressors (single/two stages) Screw-type (worm) compressors Diaphragm-type compressors Membrane compressors Sliding-Vane rotary compressors Helical compressors Root compressors Turbo (axial or radial flow) compressors

Compressor Cooler Check Valve Block Typical picture of a Piston Compressor

  

Suction Port

Suction Valve

Pressure Valve

Pressure Port

    

The most frequently used compressors are and piston compressors screw-type compressors and both operate according to the displacement principle. principle. They are suitable for pneumatic systems, where low, middle or high air pressure is needed. Both compressor types are designed for maximum delivery quantities (volumetric flow) in the range from approximately 30,000 to 40,000 m 3 / h

Cooling Ribs

Piston Crank Shaft Mechanism

Compressor Block

Cross-sectional view of the component’s construction

The piston compressor generates pressure up to a maximum of 1000 bar. The screw-type compressor generates pressure of about 25 bars.

Piston Compressor ( Standardized Symbol according to DIN ISO 1219 )


4

Mode of Operation

Piston Suction Port

Pressure Port

Compressed Air

Cylinder

Drive Shaft Crank Shaft

One of the main parts that convert mechanical to pneumatic energy in piston compressors is the piston. The piston performs linear reversible motion in the compressor cylinder. This is achieved by converting the rotary motion of a drive shaft by a counterbalanced crankshaft, to which the piston is mechanically connected. The drive shaft of the compressor is normally powered by an electrical motor, which is the source of mechanical energy. A specific construction characteristic in piston compressors is the fact, that the suction port and the pressure port are physically disconnected by the respective suction or pressure valves. Suction Valve

Pressure Valve

Suction Valve

When the piston moves from the BDC to the TDC, the suction valve closes. The air trapped in the cylinder volume is compressed by the piston. The compressed air opens the outlet pressure valve and flows in the subsequent component of the pneumatic power supply. This motion of the piston is called the compressing motion.

SUCTION FILTER The suction filter partially cleans the air driven in a pneumatic system. The suction filter is normally place on the suction port of pneumatic compressors.

Suction Filter

Pressure Valve

CHECK VALVE

Suction Stroke The top-most position, which the piston may reach in the cylinder, is called the top dead center (TDC). Similarly, the lower-most position is called the bottom dead center (BDC). When the piston moves from the TDC to the BDC the pressure valve is closed. The atmospheric air flows through the inlet suction valve into the piston area. This motion of the piston is called the suction stroke.

The check valve, also known as n on-return valve allows the compressed air to flow in only one direction. It is normally fitted after the piston compressor to protect the latter from receiving backflow of compressed air.

Typical picture of a Check Valve

Check Valve


5

COOLER The cooler is a device which brings down the temperature of the compressed air in pneumatic systems. This is needed for the normal operation of pneumatic systems.

Cooler

FILTER WITH WATER TRAP The purpose of this component is to clean the air form solid and liquid contaminants. These contaminants flow down to the base of the filter unit and can be drained off by opening the draining screw at the bottom.

Typical picture of a Reservoir

Reservoir

PRESSURE SWITCH The pressure switch is an example of PE converter because it controls the on and off switching state of the electric motor that drives the piston compressor. It is used to establish and maintain pressure in pneumatic systems at a specified level by turning the electrical motor off once the specified accumulated pressure is achieved.

Typical picture of a Filter with Water Trap

Filter with Water Trap

RESERVOIR The reservoir also known as a pneumatic capacitor or a pressure accumulator is a specific accumulator of pneumatic energy. It is placed in pneumatic systems to perform the following basic functions:  

accumulates pneumatic energy provides back-up pneumatic energy to balance the changes in the pressure of the system

Typical picture of a Pressure Switch

Pressure Switch


6

PRESSURE RELIEF VALVE The pressure relief valve is used to establish and maintain pressure in pneumatic systems at a specified level. This enables the simultaneous achievement of the following aims: 



maintain the pressure level at a value needed for the normal operation of the pneumatic system protects the pneumatic system from a dangerous pressure overload which may lead to accidents

Typical picture of a Pressure Gauge

Pressure Gauge

THERMOMETERS Thermometers are devices that are inserted in the pneumatic power supply to monitor the temperature of the compressed air in pneumatic systems. This is needed for maintaining the normal operation of pneumatic systems.

Typical picture of a Pressure Relief Valve Thermometer

HAND-SLIDE VALVE Pressure Relief Valve

It acts as the main pneumatic switch of the pneumatic power supply for the pneumatic installation.

PRESSURE GAUGES The pressure gauge is a device which measures and indicates the operating pressure at certain points in the pneumatic system. It is used for the following main purposes: 



to monitor the pressure level at a specific point in the pneumatic system; to pre-set the pressure level to a certain point in the pneumatic system.

Typical picture of a Hand-slide Valve

Hand-slide Valve


PNEUMATIC POWER SUPPLY DIAGRAM Thermometer

Pressure Gauge

7

COMPRESSED-AIR ENERGY

Reservoir

Pressure-Relief Valve

Shut-off Valve

Compressed air is generated and conditioned in a central compressed-air unit and is then distributed in the installation through the compressed-air network. Compressed air represents one of the oldest known forms of energy. This pneumatic energy is generated by the compression of air in the pressure tank and which is subject to atmospheric pressure. PABS = PAMB + PE

Where: PABS PAMB Pressure Switch

PE





Check Valve Compressor

Cooler Filter with Wate Wa terr Tra Tra



Suction Filter

Typical Pneumatic Power Supply

= Absolute Pressure = Ambient / Atmospheric Pressure = Gauge / Operating / Working Pressure

Normal operating pressure of a pneumatic installation is between PE = 4 to 10 bar. Pneumatic elements operating in the lowpressure area is between PE = 0.2 to 0.5 bar. Vacuum devices operate with a negative gauge pressure between PE = -0.6 to -0.8 bar.

INHERENT PROPERTIES IN PNEUMATIC ENERGY    

          

Availability Transportability Storability Environmental influences like dust, dampness and temperature Explosion hazard Cleanliness Working speed Overload capacity Working speed control Energy cost Energy preparation Signal speed Constant working movements Forces and torques Noise


COMPRESSED–AIR PREPARATION AIR COMPRESSION

8

Dew is moisture from the air that has condensed as tiny drops on outdoor objects and surfaces that have cooled.

g/m3

110 PRESSURE INCREASES

TEMPERATURE INCREASES

90 70

COOLING

DRYING WATER VAPOR

50 30

WATER REMOVAL 







When air is compressed, compressed-air energy is generated and the compressed-air temperature rises. Due to the law of physics, the compressed air can also absorb a certain amount of water vapor. The higher the temperature and the larger the volume, the more vapor is in the compressed-air. This means that water collects naturally in the reservoir. Water vapor and the attendant of contamination phenomenon impair the correct functioning of the pneumatic control, among of which are corrosion and freeze-up, and danger of seizure. The compressed-air is therefore always dried or cooled downstream of the compressor.

DEW-POINT CURVE The dew-point curve shows the air’s capacity for absorbing water in g/m 3 as a function of the air temperature. The temperature at which the air cannot hold all the moisture in it and dew begins to form. If objects and surfaces have cooled to below freezing point when the moisture in the air begins to condense, frost is formed instead.

0

20

40

60

80

Degrees Celsius

Dew-point Curve

COMPRESSED–AIR DRYING AND COOLING METHODS ABSORPTION DRYING

It is the chemical process in which the air flows over a desiccant which binds the air and dissolves in the process. A desiccant is a substance that absorbs water and can be used to remove moisture. The resulting condensate must be removed at regular intervals and the desiccant renewed. r enewed. ADSORPTION DRYING

Adsorption is the process by which a layer of atoms or molecules of a substance, usually a gas, is formed on the surface of a solid or liquid. In this process, the air is alternately switched back and forth by means of check valve control between two containers which are filled with a desiccant which absorbs the water vapor. Hot air is then blown through the wt desiccant to dry it. COMPRESSED-AIR COLD DRYING

The temperature of the compressed air is reduced to 2 degrees Celsius by a refrigerating plant. The water which forms is then removed.


COMPRESSED-AIR DISTRIBUTION The input of pneumatic energy takes place through the main line through the use of pipes. At the machine itself, distribution is usually through plastic hoses. Correct dimensioning and routing of pipeline network and of the hose lines is an important factor in the provision of an efficient and non-fluctuating supply of pneumatic energy.

FACTORS WHICH DETERMINE THE CORRECT DIMENSIONING OF PIPES AND HOSES ARE:

1. 2. 3. 4.

Flow quantity Length of the line Permissible pressure loss Operating pressure

DE-CENTRALIZED COMPRESSEDAIR PREPARATION Due to the fact that the water and the other contamination are to be expected in the line network, an Air-service Unit should be located directly in the installation for renewed conditioning of the air. As a rule the air service unit is placed between the compressor and the rest of the pneumatic system. The air service unit is an integral part of all pneumatic systems. It is a device incorporating an air filter with water trap , a pressure regulator (pressure reducing valve) as a minimum configuration and in some cases with pressure gauge and oil-fog lubricator.

THE PURPOSE OF AIR SERVICE UNIT 



MAIN PIPELINE LAYOUT FOR PNEUMATIC SYSTEMS BRANCH LINE

This is the simplest form of pipeline

9





To clean the compressed air from dust/dirt and particles that might reach the cylinders and valves of the system. This will increase the life of the components in the system. To separate the moisture/water from the compressed air. This avoids rust of the pneumatic components. To regulate and maintain a constant air pressure in the system. To lubricate the compressed air with oil.

layout. RING MAIN

3/2 way Shut-off Valve

Pressure Regulator

Filling Valve

3/2 way Shut-off Valve

This is the most common line layout having the advantage of providing uniform supply of compressed air due to the input of air from both directions. COMPOUND NETWORK

This is a form of ring main layout which is expanded by the addition of longitudinal and transverse connection lines. This method permits connections to be made over a large area. Shut-off valves can be installed to permit sections of the network to be isolated for repair or servicing.

Note that the pipes and hoses are commonly connected together using fittings and couplings.


Pressure Gau e

Lubricator

Typical picture of an Air-service Unit


Dosing Screw

Pressure Regulator Deflector Tunnel

Filler Plug

Sinter Filter Element

Atomizer Nozzle

Condensate Drain

Deflector Plate

10

Compressors normally supply unclean compressed air to pneumatic systems. This air is fed into the inlet of the air-service unit and will pass through the filter with water trap where it is caused to rotate through the deflector tunnel by a vortex insert (a whirling mass of air that draws everything near it towards the center). The centrifugal force flings the water held by the compressed air to the outside and it then collects in the base of the water trap. The filter will separate the solid and liquid contaminants from the air. Solid contaminants (dust/dirt) may block the normal operation of a number of pneumatic components. Liquid contaminants (mainly water) lead to internal corrosion of pneumatic components.


Air-service Unit Filter Reservoir

Air-service Unit

Mode of Operation

Unclean Compressed Air

Inlet

Draining Screw

Deflector Plate

The contaminants flow down below the deflector plate, which will prevent them from being sucked back up into the vortex. The contaminants will collect in the bottom of the filter reservoir for proper disposal. Any remaining fine particles will be trapped in the filter element as the air passes through and the cleansed air exits the filter through the outlet port. The contaminants and condensed liquids, collected in the bottom of the filter unit should be drained regularly by manually opening the draining screw or by means of an automatic condensate drain valve. This maintenance action would guarantee the continuous supply of clean compressed air in the system.

Sinter Filter

Pneumatics Technology Main Pressure

Pressure Re ulator

Compressed Air

11

From the regulator the clean regulated air will pass into the lubricator. Note that all pneumatic systems need lubrication so we should refer to the individual component specifications. In the lubricator the compressed air flows through an atomizer nozzle (a device that converts a liquid into a fine spray), where the air and lubricating oil are combined. The amount of lubricating oil the system requires is regulated by the dosing screw. Regular maintenance of the oil-mist lubricator requires the control of lubricating oil in the oil reservoir. If a lubricator is used, the oil level must be maintained otherwise the system components can fail.

Operating Pressure The cleaned compressed air is then passed through a fine-pored sinter filter to the filter-unit’s outlet. When the compressed air enters the regulator, the cleansed supply air ( primary pressure) will be regulated to the desired secondary pressure (operating pressure). The secondary pressure (operating pressure) will exit the regulator through the outlet port.

FILTER WITH WATER TRAP The purpose of this component is to clean the air form solid and liquid contaminants. These contaminants flow down to the base of the filter unit and can be drained off by opening the draining screw at the bottom.

Note that the supply pressure (primary pressure) must be higher than the system pressure (secondary pressure). Normally there is a pressure gauge inserted to indicate the operating pressure.

Atomizer Nozzle

Dosing Screw

Typical picture of a Filter with Water Trap


Oil-mist Lubricator

Oil Reservoir


12

PRESSURE REGULATOR The pressure regulator (known also as pressure reducing valve) is a component having two ports - an inlet and an outlet port. It maintains s constant pressure at the outlet port, which is lower than the pressure at the inlet port. It reduces the main pressure to a given (adjustable) operating pressure, and maintains it at this level even when the loads and mains pressure fluctuate.

Pressure Regulator Mode of Operation

Diaphragm Outlet Port

Inlet Port

The outlet pressure does not depend on the inlet pressure, as well as on the air flow rate. The outlet pressure depends only on the setting of the pressure regulator. Additionally, in cases of overloading of the outlet line by external sources of energy, the pressure regulator limits the value of the outlet pressure Adjustment Knob

Pressure Regulator Housing

Inlet Pressure Port

Gap 1

Gap 2

The pressure regulator is in initial position, when the pressure at its inlet and outlet ports is equal to the atmospheric pressure. The diaphragm and the valve are counterbalanced under the action of the forces of the atmospheric pressure and the compression of both springs. The gap 1 is open and gap 2 is closed. There is not air flow through the regulator.

Outlet Pressure Port

Pressure Gauge

Outlet Port

Inlet Port

Typical picture of a Pressure Regulator Adjustment Knob

Big Spring Diaphragm

Gap 2 Outlet Pressure Port

Inlet Pressure Port

Small Spring

Gap 1 Valve

Housing


Gap 1

Valve

Diaphragm

When the inlet pressure increases to a level, higher than the atmospheric pressure but lower than the pressure , at which the regulator is pre-set , the compressed air flows from the inlet port through gap 1 towards the outlet port. The diaphragm and the valve are again in initial position. The outlet pressure is equal to the inlet pressure.

Pneumatics Technology Large Spring Inlet Pressure

Gap 1

Adjustment Knob Outlet Pressure

Valve

Diaphragm

When the inlet pressure rises to a level, higher than the pressure, at which the regulator is pre-set , the diaphragm and the valve move in a direction which compresses the large spring . This movement will stop at the position, when both the valve and the diaphragm are again counterbalanced. This position is determined under the action of the forces of the inlet pressure, the atmospheric pressure and the deformation of both springs. Consequently, the size of gap 1 is reduced. This creates a pressure drop in the regulator. As a result, the outlet pressure is lower than the inlet pressure.

Inlet Pressure

13

Constant Outlet Pressure

Large Spring

Inlet Pressure

Gap 1

When the inlet pressure decreases or when the air flow rate increases, the diaphragm and the valve move in a direction towards decompressing the large springs and the pressure. As a result, gap 1 increases and the value of the pressure drop in the regulator will decrease. Again, this movement will continue, until the valve and the diaphragm are counterbalanced by the forces, thus maintaining a constant value of the outlet pressure. The adjustment knob of the pressure regulator pre-sets the value of the outlet pressure. By turning it clockwise the outlet pressure will increase and vice versa. Orifice in Regulator Housing Inlet Port

Gap 1 Narrowing of Gap 1 A further increase of the inlet pressure or a decrease in the air flow rate will lead to the same reaction of the parts of the regulator. The result is the further narrowing of gap 1 which creates a bigger pressure drop in the regulator. This is the way a constant outlet pressure is ensured.

Valve

Outlet Pressure

Valve Pin

Diaphragm Higher Pressure at Outlet Port

Gap 2

Sometimes an external source of energy creates very high pressure value in the outlet line of the regulator. In cases like these, the diaphragm deforms to an extent, where it shrinks the large spring and gets detached from the valve pin. This opens gap 2, which connects the outlet port to the atmosphere through the orifice (opening) of the diaphragm and the orifice in the regulator housing. Hence, the excessive pressure starts discharging.


In the same time, the big spring no longer counterbalances the valve against the force of the small spring. Consequently, the vale moves to the position, when the valve disk closes gap 1 and no further pressure is provided to the system for the inlet of the regulator. This state of the regulator will be maintained, until the high pressure on the outlet port drops to a level, lower that the presetting of the regulator. When that happens, the diaphragm moves back to the point, when gap 2 is closed and the pressure regulator starts to operate as described in the initial pages.

OIL-FOG LUBRICATOR OR OIL-MIST LUBRICATOR The oil-fog lubricator operates according to the Venturi principle (a constriction in a tube designed to cause a pressure drop when a liquid or gas flows through it) by which the vacuum resulting from a reduction in area, oil is drawn up through a narrow pipe which reaches into the lubricator’s oil reservoir. The oil then dips into the compressed air as it passes through and forms as a fine fog.

PRESSURE GAUGE OF THE PRESSURE REGULATOR A typical pressure regulator is normally fitted with a pressure gauge to indicate the operating pressure at the outlet port. Adjustment Knob

Pressure Regulator Housing Typical picture of an Oil-fog Lubricator

Inlet Pressure Port Oil-fog Lubricator

Pressure Gauge

Outlet Pressure Port

Typical picture of a Pressure Gauge

Pressure Gauge

14


15

SUPPLEMENTARY COMPONENTS FOR THE AIR-SERVICE UNIT

PRESSURE DISTRIBUTOR WITH NON-RETURN VALVES

FILLING VALVE

They are inserted between the pressure regulator and the oil-fog lubricator to ensure that the signaling elements are supplied with oil-free air.

A filling valve prevents a sudden increase in pressure when the system is switched on. MICRO-FILTER

Relief and Sequence Valve Additional Micro-Filter

A supplementary micro-filter is added to further remove the contaminants.

Oil-Free Compressed Air Rapid-Exhaust Valve

RELIEF VALVES

They are used to relieve the air-service unit from excessive pressure fluctuations. They are inserted in the upstream and downstream of the air-service unit or between the individual items of equipment.

SEQUENCE VALVES

The sequence valve is usually located on the supply line of a cylinder or on a branch of a pneumatic circuit that is isolated from the main circuit. When the pressure in the main circuit reaches the set pressure of the sequence valve, it opens and lets air flow to the cylinder or to the branch of the circuit.

RAPID-EXHAUST VALVES

They are used to stipulate that cylinder movements are to take place as quickly as possible.

Supplementary Components For the Air-service Unit

Lubricated Compressed Air


3.

DRIVE ELEMENTS

16

Bellows-type Cylinders Note that bellows is a device or piece of equipment with a compressible chamber with flexible sides that can be expanded to draw air in and compressed to force the air out. Diaphragm or bellows-type cylinders can have diameters of up to 710 mm. They can generate forces of up to 190 kN at pressures of 7 bars. 

Pneumatic drive elements convert the energy in the compressed air into force and motion. The pneumatic drive elements can move in a linear, reciprocating or rotating motion.



SINGLE-ACTING CYLINDERS



The single-acting cylinder converts the compressed air energy into mechanical energy in the form of force and linear movement in one direction only.

Pressure Port

Cylinder Tube

Cylinder Rod

The cylinder has two ports - a pressure inlet port and an exhaust port. The annular area (shaped like or forming a ring) of the cylinder is connected to the atmosphere The compressed air is applied only on the bottom side of the piston that is why the cylinder can move loads or perform mechanical work in a forward motion only and that the effective force is reduced by the return spring . Single-acting cylinders are used in the assembling and packing automated lines to move, lift, feed, eject, press or push objects or to clamp parts. Practically, they are suitable for oilfree operation.

Exhaust Port Cylinder Cover

Cylinder Bottom

Typical picture of a Single-Acting Cylinder

Pressure Port

Exhaust Port Piston

Rod

Spring

Types of Single-Acting Cylinders

1.

Piston cylinders Note that a piston is a metal cylinder that slides up and down inside a tubular housing, receiving pressure from or exerting pressure on a fluid. Typically, the piston can have diameters of as much as 100 mm. The working speed is in the range of 50 to 500 mm/s. Cylinder forces are about 4 kN. 



Piston Area

Bush & Sealing Element

Base end Cover

Tube Annular Area

Head end Cover






2.

Short-stroke Cylinders Note that the length of stroke is the actual working movement. The shorter stroke enables the cylinder to lift heavy loads. They can also be equipped with an anti-rotation anchor, external guidance and a magnetic ring for triggering noncontact signaling elements. 

Single-Acting Cylinder, Spring Return


17

Piston Area

Mode of Operation

Piston Area

Piston

Spring

Cylinder Bottom

When the piston area of the cylinder is connected to the atmosphere, the piston of the single-acting cylinder is pressed by the spring to the cylinder bottom.

Spring

When the piston area of the cylinder is again connected to the atmosphere, the piston of the singleacting cylinder is pressed by the spring to the cylinder bottom (return stroke) thereby generating a vacuum at its rod side which draws in air through the vent hole. The vent hole is provided with filter if the working surroundings are not dust free. Special versions of the Single-acting cylinder

An alternative construction is a single-acting cylinder, spring extend with a spring in the piston area causing the piston to extend. Such pistons are used in the automotive industry and these are mounted in the air brakes for vehicles and trains.

Piston Area

Single-Acting Cylinder, Spring Extend

Piston

Spring

Another special form of single-acting cylinders is single-acting cylinder, without return spring in which the piston’s return stroke is caused by external forces or by its own weight. Load

When the piston area is connected to the pressure line, the piston of the single-acting cylinder will move forward ( outward stroke) against the force of the return spring . The air on the rod side is forced out through the vent hole which must always be open.

Single-Acting Cylinder, without Return Spring


DOUBLE-ACTING CYLINDERS

Cover

Port

Tube

18

Port

The double-acting cylinder converts the compressed air energy into mechanical energy in the form of force and linear movement in both directions. This type of cylinder has two ports. The compressed air is applied at one of the working ports while the other working port is vented. They are used when the piston rod must perform work during its return stroke and when longer strokes are needed. When large loads are moved, double– acting cylinders with adjustable stroke cushioning are to be used in order to avoid shocks at the cylinder bottom or cover. Such cylinders have two plungers (part of the device that thrusts or drops downward) on both sides of the piston. By means of two damping pistons and cap seals, an air cushion is formed which is then exhausted through the adjustable throttle. The air which flows in quickly becomes effective due to the fact that the caps seals open up. Double acting cylinders are used for moving, pressing and lifting in pneumatic manipulators and automatic packaging machines. Types of Double-Acting Cylinders

1.

Piston cylinders Stroke lengths are up to 500 mm. The working speed is in the range of 30 to 2000 mm/s. Cylinder forces are about 40 kN. 

Piston

Adjustable Throttle

Rod

Typical picture of a Double-Acting Cylinder

Cushion / Bottom Cap Seal

Plunger

Adjustable Throttle

Tube

Piston Area

Piston

Port

Cover

Annular Area Cross-sectional view of the component’s construction





2.

Short-stroke Cylinders Short-stroke cylinders are used when short strokes are required together with high forces. 

Double-Acting Cylinder Typical picture of Short-stroke Cylinders Double-Acting Cylinder with Adjustable Stroke Cushioning

Rod


19

Mode of Operation

Piston Area

Piston

Piston Area

Annular Area

When the piston area is connected to the pressure line and in the same time the annular area is connected to the atmosphere, the piston of the double acting cylinder moves forwards.

Piston Area

Piston

Rod-cushioning Plunger

Forward cushion Throttle

Cushion Seal

At the end of the forward stroke the rod-cushioning plunger will engage the cushion seal and this will trap the exhausting air in the annular area. The exhausting air is forced through the forward cushion throttle, decelerating the forward movement of the piston to a stop. The purpose of the cushion is to avoid on uncontrolled shock caused by the piston hitting the cylinder end-head at the end of the stroke.

Piston

When the annular area is connected to the pressure line and in the same time the piston area is connected to the atmosphere, the piston of the double acting cylinder moves backwards.

Backward cushion Throttle

Rod-cushioning Plunger

Cushion Seal

When the piston reaches the end of the backward stroke, the rod cushioning plunger will engage the cushion seal and this will trap the exhausting air in the piston area. The air is forced through the backward cushion throttle, decelerating the backward movement of the piston to a stop. As with the forward cushion, the purpose is to avoid an uncontrolled shock at the end of the stroke .


20

ROTARY ACTUATORS The rotary actuators transform the power of compressed air that generates linear piston movement into a reversible rotary movement. The piston rod of the actuator is designed in the form of a toothed rack with two pistons connected at each end. The linear motion created by introducing an air pressure to the piston/rack assembly is transmitted through a pinion (small gear wheel that engages with a larger gear or with a rack) to create a rotary motion. The rotation angle could reach and even overcome 360° depending on the cylinder stroke and on the gear ratio. The chamber between the two pistons is connected to the atmosphere, to avoid any trapped air from impeding any motion of the actuator. Available torque at the shaft is directly proportional to the difference in air pressure between the input and output ports. Rotary actuators are used for turning details, bending pipes and bars, or for driving butterfly valves in pneumatic control systems. Port

Tube

Rotary Actuator Mode of Operation

Left Piston

Left Piston Area

Right Piston Area

Left Cylinder Cover

When the left piston area is connected to the atmosphere and in the same time the right piston area is connected to the pressure line, the left piston is pressed to the left cylinder cover.

Left Piston Area

Rack

Port

Pinion

Cover

Shaft with Pinion

Cover

Right Piston Area

Similarly, when the left piston area is connected to the pressure line and the right one is connected to the atmosphere the two pistons with the rack move to the right and the rack turns the pinion clockwise.

Typical picture of a Rotary Actuator Left Piston

Cover

Piston

Rack

Tube

Piston

Pinion


Left Piston Area

Cover

Port

Left Cylinder Cover

Right Piston Area

Again, when the left piston area is connected to the atmosphere and the right one is connected to the pressure line the two pistons with the rack move to the left and the rack turns the pinion counter clockwise.


21

OTHER SPECIAL ACTUATORS SLIDE UNITS A slide unit is a precision linear actuator of compact dimensions which can be used on manufacturing and assembly robotic machines. Precise machine work mounting surfaces and parallel piston guide rods ensure accurate straight line movement when built as part of the construction of a transfer and position machine. 



In one position, the body can be fixed and the rods with end bars can move. Upside down, the end bars can touch the mounting surface and the body can move.

Typical picture of a Rodless Cylinder

Rodless Cylinder

HOLLOW ROD CYLINDER The hollow rod cylinder provides a direct connection between vacuum generating equipment and a vacuum pad attached to the rod working end. The connecting tube at the rear end of the cylinder remains static, while the rod extends and retracts. They are specifically designed for pick and place applications.

AIR CHUCK OR FULCRUM-TYPE GRIPPER Typical picture of Slide Units

An actuator designed to grip components and workpieces in robotic-type applications

RODLESS CYLINDER The Rodless cylinders are particularly suitable for very long piston strokes. A carriage is magnetically attached to the cylinder which was made of a non-magnetic material like brass, by way of the magnetic piston.

Typical picture of a Pneumatic Gripper Typical picture of a Rodless Cylinder


22

DOUBLE-ENDED ROD CYLINDERS

DIFFERENTIAL CYLINDERS

The double rod cylinder can be used to drive a long stroking workpiece attached to the cylinder housing. Guiding and rigidity is obtained by the piston rod ends when they fixed on side walls thus the cylinder moves with attached workpiece.

The differential cylinder has a larger piston diameter compared to its linear counterparts.

BELLOW CYLINDER

TANDEM CYLINDERS A tandem cylinder is two double acting cylinders joined together with a common piston rod, to form a single unit. By simultaneously pressurizing both cylinder chambers, the output force is almost double that of a standard cylinder of the same diameter. It offers a higher force where installation spaces are restricted.

A bellows is a device or piece of equipment with a compressible chamber with flexible sides that can be expanded to draw air in and compressed to force the air out. For the bellow cylinder to inflate, the input pressure must be greater than the trigger pressure. When the input pressure is less than the trigger pressure, the bellow cylinder begins to deflate and return to its initial state. Two proximity sensors can be used to detect the cylinder's expansion.

Bellows-type Cylinder

VANE-TYPE ROTARY ACTUATOR MULTI-POSITION CYLINDERS The two ends of a standard cylinder provide only two fixed positions. If more than two fixed positions are required, a combination of two double-acting cylinders may be used. For three positions, it is still possible to fix the cylinder. They are however suitable for vertical movements such as in handling devices.

This type of cylinder also converts the compressed-air energy into rotational or back and forth movement. Air pressure acts on a vane (flat blade mounted as part of a set in a circle so as to rotate under the action of air pressure) which is attached to the output shaft. The vane is sealed against leakage by a fitted rubber seal or elastomer coating . A special three-dimensional seal seals the stopper against the shaft and the housing. The size of the stopper defines the rotation angle of 90, 180 or 270 degrees. Adjustable stops may be provided to adjust any angle of rotation of the unit. 



LOCKING CYLINDERS COMPRESSED-AIR MOTOR A cylinder can be fitted with a locking head in place of the standard end cover. It will hold the position of the rod in any position. The locking action is mechanical ensuring the piston rod is securely held even under full load.

The compressed-air motor converts the compressed-air energy into rotational movement. Available torque for the shaft is directly proportional to the difference in air pressure between the input and output ports. The output port of a one direction motor is usually connected to the exhaust and is fitted with a muffler.


ACTUATORS, CONTROLLING ELEMENTS AND SIGNALING ELEMENTS





Valves are devices that controls the flow or movements of fluids like liquids or gases through piping or other passages by opening or closing ports and channels

DIRECTIONAL CONTROL VALVES In pneumatic controls, directional control valves determine the flow of air between its ports by opening, closing or changing its internal connections. They are used as signaling elements, controlling elements and actuators to perform functions like:



stopping the flow of compressed air controlling the through-flow of air controlling the direction of flow of air

  

Direct Exhausts are called open-air exit but it does not accept any connection to a distributor. Exhausts are called restricted-air exit The exhaust acts as a pressure reducer and are inserted in the circuit wherever there is an exhaust port. It allows the evacuation of compressed air so that pressure will be null in all the parts of the circuit to which they are attached. Switching positions and their respective control methods can be identified using lower case letters. a



23

b

a

0

b

Normal Position of the valve is defined as the switching position assumed by the valve when it is not operated, say for instance due to the force of the spring.

CLASSIFICATION OF DIRECTIONAL CONTROL VALVES    



type of control type of the distributing element number of pneumatic connections or ports condition at neutral position whether normally closed and normally open valve

REPRESENTATION OF DIRECTIONAL CONTROL VALVES Pneumatic elements are shown as standardized symbols as stipulated in DIN ISO 1219. Switching Position

Fittings

Line Connections

Exhaust or Vent

Pneumatic Pressure Source

Internal Direction of Flow Connections

Direct Exhaust

Blocks

Initial Position of the valve is defined as the switching position assumed by the valve for instance to mechanical detent or due to the switching-in of supply energy.

PORT OR CONNECTION DESIGNATION OF DIRECTIONAL CONTROL VALVES PORT

DESIGNATION

LETTERS

ISO 5599

INPUTS (Supply)

P

1

OUTPUTS (Working Ports)

A, B

4, 2

VENTS (Exhaust Ports)

R, S

5, 3

PILOT (Control Ports) For 3/2 DCVs

Z, Y

12, 10

PILOT (Control Ports) For 4/2 and 5/2 DCVs

Z, Y

14, 12


DESIGNATION OF DIRECTIONAL CONTROL VALVES 2/2 way On/Off DCV without exhaust

2/2 way Normally Open DCV

3/2 way Normally Closed DCV

24

CONTROL OR ACTUATION METHODS OF DIRECTIONAL CONTROL VALVES The control or actuation methods are used to switch-over between the valves various switching positions. They are drawn directly at the side of the square as it represents the directional control valve’s switching position to which it applies. The following are the common valve operators: 1.

MANUAL / MUSCULAR CONTROL Generally obtained by attaching an operator head, suitable for manual control, onto a mechanically-operated valve. Manually-operated, monostable valves (spring return valves) are generally used for starting, stopping and otherwise controlling a pneumatic circuit. In circumstances where it is more convenient if the valve maintains its position, manually-operated bistable valves (with detent or impulse) should be used. 

3/2 way Normally Open DCV



4/2 way DCV (14) with a common exhaust



4/2 way DCV (12) with a common exhaust

5/2 way DCV (14) with separate exhausts

2.

MECHANICAL CONTROL On an automated machine, these valves can detect moving machine parts to provide signals for the automatic control of the working cycle. 

5/2 way DCV (12) with separate exhausts 3.

PNEUMATIC / PRESSURE CONTROL Normally, air-operated valves are the main valves which are located close to a cylinder or other actuator, and are switched by remote control from signal input valves or switches. A monostable air-piloted valve is switched by air pressure acting on a piston and returned to its normal position by an airspring , mechanical spring , or a combination of both, when the signal pressure is removed. 

3/3 way DCV with a closed-center position

4/3 way DCV with an open-center position



5/3 way DCV with an open-center position

5/3 way DCV with a closed-center position

5/3 way DCV with a pressurized-center position  

The 1st digit = Number of Ports The 2nd digit = Number of Switching Positions

4.

ELECTRICAL CONTROL The electrical operation is effected by a solenoid and a plunger, and therefore the units are generally known as solenoid valves. Direct acting solenoid valves rely on the electromagnetic force of the solenoid valve to move a poppet or spool. To limit the size of the solenoid, larger valves have indirect solenoid pilot operation. 






MANUAL CONTROLS

MECHANICAL CONTROLS

PNEUMATIC CONTROLS

ELECTRICAL CONTROLS

NAMING DIRECTIONAL CONTROL VALVES

25

Pneumatics Technology 2

3/2 MANUALLY OPERATED DIRECTIONAL CONTROL VALVES 12 The 3/2 directional control valve (DCV), manually operated, is used to control the direction of the air flow in a single line of a pneumatic system. It connects the outlet port of the valve to its pressure inlet or exhaust port. 3/2 DCV allows manual or mechanical control of the pneumatic air flow in the circuit.

26

10 3 1

3/2 way Normally Closed Directional Control Valve, Push-button Actuated, Spring Return

They are used to provide input control of power signals given by an operator or by moving mechanisms of the system. The 3/2 directional control valves are also used for the direct for the direct actuation of single-acting cylinders. Port 2

Housing

Typical picture of a 3/2 way Normally Open Directional Control Valve, Push-button Actuated, Spring Return

Outlet Port

Distributing Spool Port 3

Port 1

Spring

Push-button

Typical picture of a 3/2 way Normally Closed Directional Control Valve, Push-button Actuated, Spring Return

Distributing Spool

Outlet Port Spring Pressure Inlet Port

Air under Pressure

Exhaust Port

Cross-sectional view of the component’s construction 2 Housing

Exhaust Port

Pressure Inlet Port

12

10 1 3


3/2 way Normally Open Directional Control Valve, Push-button Actuated, Spring Return


27

Mode of Operation 3/2 way Normally Closed Directional Control Valve, Push-button Actuated, Spring Return Outlet Port

Outlet Port Spool

Spool

Pressure Inlet Port

Exhaust Port

The return spring will maintain the normal position (unactuated) of the spool. The normally closed valve in the normal (unactuated) position, air can pass from port 2 to port 3 and port 1 is isolated. Outlet Port Spool

Exhaust Port

Pressure Inlet Port

When the button is actuated (the button is pushed), the spool changes position. This opens the connection between port 1 and port 2 and isolates port 3 from the other ports. The spool will remain in this position until the button is released.

Exhaust Port

Pressure Inlet Port

When the button is released the return spring will reposition the spool to the normal position.


28

3/2 way Normally Open Directional Control Valve, Push-button Actuated, Spring Return

Outlet Port

Outlet Port

Spring Spool

Spool

Pressure Inlet Port

Air under Pressure

Exhaust Port

The return spring will maintain the normal position (unactuated) of the spool. In this condition air can pass from port 1 to port 2 and port 3 is isolated from the other ports. Outlet Port

Spool

Pressure Inlet Port

Exhaust Port

When the button is pressed (actuated) the spool changes position. In the actuated state, air can pass from port 2 to port 3 and port 1 is isolated from the other ports. The spool will remain in the position until the button is released.

Pressure Inlet Port

Air under Pressure

Exhaust Port

When the button is released, the return spring will push the spool back to the normal position and air can pass from port 1 and port 2, and port 3 is isolated from the other ports again.


5/2 PNEUMATICALLY OPERATED DIRECTIONAL CONTROL VALVES Basically, the 5/2 directional control valve functions the same as the 4/2 version. The only difference being that due to its design as a spool valve, the 5/2 has an additional exhaust port (5). In practically all applications, it is just as suitable as the 4/2 version but because of its outstanding features in terms of size, easy actuation and air passage being possible in both directions, the 5/2 is sometimes actually preferable to the 4/2 version. The principles of operation of the pneumatically operated 5/2 directional control valve is dependent upon the movement of the spool inside the valve. The component shifts the connection between two outlet ports with a pressure inlet port and an exhaust port. By this means, pneumatic control of the system is achieved. In such valves, normally outlet ports are indicated as 2 and 4, pressure port 1, and exhaust ports 3 and 5.

Control Input

Housing

Valve Spool

Exhaust Port

Outlet Ports

Pressure Inlet Port

5/2 way Pneumatic Impulse Valve

The 5/2 directional control valve, operated by pneumatic impulse, is applied in various practical solutions such as pushing off details, applying tools for performing operations, opening/closing doors and windows, stretch/bend robot/manipulator arms. Housing

Side Cover

Typical picture of another version a 5/2 way Pneumatic Impulse Valve

Exhaust Port 3

Outlet Port 2

Pressure Port 1

Outlet Port 4

Exhaust Port 5

Typical picture of a 5/2 way Directional Control Valve, Pneumatically Actuated Both Ways

Control Input

Exhaust Port


The position of the valve spool is retained until a short pneumatic control signal is applied to any of the control ports.

Side Cover

29


PNEUMATIC IMPULSE VALVES

30

Mode of Operation

Impulse valves have two switching positions and compressed-air control from both ends is used for storage of pneumatic signals (commands). Such valves have no normal position and are controlled by pneumatic pulses ( brief signals). They are often called as pneumatic memories or pneumatic memory valves or flipflop valves. Regarding the design principle, impulse valves are usually of the spool type. There are a number of special versions available though in the form of floating –plate and the sliding spool valves. Using a pneumatic control impulse, pressure is applied to the impulse valve through one of the pilot ports 12 and 14. The valve switches to the required position. When the control pulse is removed, the valve remains in the given switching position until a second counter-control impulse is applied at the other pilot port. Normally, the valve switching position (spool position) is retained when the control pulse is removed due to the inherent sticking friction of the spool or the O-rings.

The 5/2 directional control valve does not have a neutral position. Switching the spool from one position to the other requires only a short pneumatic control impulse at the respective control port (pilot port). When applying a control impulse signal to pilot port 12, the spool is shifted to the position as shown on the figure above. The pressure inlet port 1 is connected to the outlet port 2 at the same time that the outlet port 4 is connected to the exhaust port 5. There is no connection to the exhaust port 3. The position of the spool is retained even when the control signal is no longer applied.

PNEUMATICALLY CONTROLLED DIRECTIONAL CONTROL VALVES In general, pneumatically controlled directional control valves are always used in the following applications: 1.

2.

3.

When a small signaling element (hand-operated valve) is to be used to control a large-volume drive element such as a cylinder with large piston diameter. When the signaling element and the actuator are a long distance apart. In practice, the pneumatic engineering maximum permitted separation is 10 meters. When a holding-element control is installed and that they must be controlled by pneumatic pulses.

When applying a control impulse signal to pilot port 14, the spool is shifted to the opposite position. The pressure inlet port 1 is now connected to the outlet port 4 at the same time that the outlet port 2 is connected to the exhaust port 3. There is no connection to the exhaust port 5. Again the position of the spool is retained even when the control signal is no longer applied.


5/2 ELECTRICALLY OPERATED DIRECTIONAL CONTROL VALVES

Electric Control

The principles of operation of the electrically operated 5/2 directional control valve is dependent upon the movement of the spool inside the valve. The component shifts the connection between two outlet ports with a pressure inlet port and an exhaust port using an electric control signal. By this means electric control of the pneumatic system is achieved. In such valves normally outlet ports are indicated as 2 and 4, pressure port 1, and exhaust ports 3 and 5. The position of the valve spool is retained until a subsequent electric control signal is applied to any of the control solenoids.

Housing

Outlet Ports

Spring

Magnet

Slug

Exhaust Port

Pressure Inlet Port

Exhaust Port


The solenoid-controlled impulse valves are controlled by electrical pulses and are normally provided with pneumatic pilot control at both ends. Usually, these valves are equipped with manual override at each end so that the valve can be switched even without electrical energy, say for instance during servicing and troubleshooting.

5/2 way Solenoid-Controlled Impulse Valve

Electrically operated directional control valves are used in electro-pneumatic systems included in material-handling systems, assembly process, opening and closing doors and windows; stretching and retracting robot arms.

Solenoid

Exhaust Port 5

Pressure Port 1

Exhaust Port 3 Typical picture of another version of a 5/2 way Solenoid-Controlled Impulse Valve

Solenoid Housing

Outlet Port 4

Outlet Port 2

Typical picture of a 5/2 way Directional Control Valve, Electrically Actuated Both Ways

31


32

Mode of Operation

The electrically operated 5/2 directional control valve does not have a neutral position. A changeover from one position of the spool to the other requires only a short control electrical impulse towards one of the control solenoids. When this happens, the solenoid slug is shifted and the air from the pressure inlet port 1 is applied to the spool head. The spool is then shifted to the opposite end position.

For example, when applying a control electric impulse signal to the solenoid 12, the pressure from the pressure port 1 shifts the distribution element in the position as shown on the figure above. The pressure inlet port 1 is connected to the outlet port 2, and the outlet port 4 is connected to the exhaust port 5. There is no connection to the exhaust port 3. The position of the spool is retained even when the electrical control signal is stopped.

Similarly, when applying a control electric impulse signal to solenoid 14, the spool is shifted to the position as shown on the figure above. The pressure inlet port 1 is connected to the outlet port 4, and the outlet port 2 is connected to the exhaust port 3. There is no connection to the exhaust port 5. The position of the spool is retained even when the electrical control signal is stopped.


DESIGN PRINCIPLES OF DIRECTIONAL CONTROL VALVES The following valve features all depend upon the design principle used for the valve: service life size actuating force type of actuation porting or connection type flow direction switching travel switching sealing-element wear

33

Poppet valves can be two or three-port valves. For a four or five-port valve, two or more poppet valves have to be integrated into one valve.

  

3



Seat

  

Elastic seal 2

 

TYPES OF DIRECTIONAL CONTROL VALVES

1

The two principal methods of construction are poppet and slide with either elastic or metal seal

Mechanically-Operated Poppet Valve For the mechanically-operated poppet valve above, the inlet pressure assists the return spring holding the valve closed.

DIRECTIONAL CONTROL VALVES

Slide Valves

Plane Slide Valves

Rotary Valves

Poppet Valves

Spool Valves

Elastic seal

1

Seat

Metal Seal

Elastic Seal

2

3

Valve types and Sealing Methods

POPPET VALVES A poppet is valve with vertical guide and that it is raised and lowered by a vertical guide, for example, the intake and exhaust valves of the cylinders in an internal-combustion engine is also called poppet The flow through a poppet valve is controlled by a disc or plug lifting at right angles to a seat, with an elastic seal.

Balanced Poppet Valve For the balanced poppet valve above, the inlet pressure acts on equal opposing piston areas. This feature allows valves to be connected up normally closed or normally open. Normally open valves can be used to lower or return pressurized actuators, but are commonly used in safety or sequence circuits.


3.

SLIDE VALVES

ROTARY VALVES

A metal-ported disc is manually rotated to interconnect the ports in the valve body. Pressure imbalance is employed to force the disc against its mating surface to minimize leakage. The pressure supply is above the disc.

Spool, plane slide and rotary valves use a sliding action to open and close ports. 1.

SPOOL VALVES

A spool is a cylinder on which thread, tape, or film is wound around. A cylindrical spool slides longitudinally in the valve body with the air flowing at right angles to the spool movement. Spools have equal sealing areas and are pressure-balanced.

2

4

2

3

1

Spool Valve 3

2.

PLANE SLIDE VALVE

The flow through the ports is controlled by the position of the slide made of metal, nylon or other plastic materials. The slide is moved by an elastomer sealed air operated spool.

1

14

12

4

5

3

Plane Slide Valve

2

34

Section through a Rotary Actuator and a Disc for a 4/3 function with closed center / exhausted center


35

VALVE SEALING METHODS Spool valves with metallic seals

Spool valves with elastic seals

The metal spool valve design means that the sealing is metal-to-metal. This necessitates the spool being precisely ground into the housing bore. This valve design needs very low actuating forces as well as having very long service life.

With this version of the spool valve, the pilot spool is sealed by low friction elastic sealing element called elastomer seal. The seals are held in their correct position by plastic rings or O-rings which are fitted in the grooves of the spool and move in a metal sleeve. Typically, the spool grooves have rounded edges so that wear is reduced when the spool passes over the seals. This valve version can be produced at a very reasonable price by using glass-fiber-reinforced plastic housings, and is also suitable for oil-free operation. Being a spool valve, it is free from overlap and through flow is possible in both directions.

These valves are overlap-free and air passage is in both directions. Lapped and matched metal spool and sleeve valves (a valve for and internal combustion engine, fitted and reciprocating inside a cylinder) have very low frictional resistance, rapid cycling and exceptionally long working life. But even with a minimum clearance of 0.003 mm, a small internal leakage occurs.

14

4

2

5

1

12

5

4

1

2

3

Spool Valve with Metallic Seals

3

Spool Valve with Elastic Seals


36

FREE-OF-OVERLAP FEATURE The poppet valve below switches due to the control plunger being forced down against the force of the spring, and due to the force acting on the pilot-piston area or the pressure area.

3

The connection between 1 and 2 and is open before the connection between 2 and 3 has closed. In other words, the valve is not free of overlap because all the connections are briefly joined with each other and pressure can collapse through the vent port.

2

1

Normally Closed Poppet Valve with Plunger Actuation and Free of Overlap 3

REVERSE-FLOW FEATURE 2

Being as it can be flowed through in both directions, this valve can be employed in either the through-flow normal position or the closed normal position.

1

Normally Closed Poppet Valve with Plunger Actuation and not Free of Overlap

To do so, it is only necessary to interchange the connections 1 and 3. However, the through-flow crosssectional area can differ in the two directions. 2

The next poppet valve is vented from port 2, through the open air exit port 3 via the passage in the pilot piston.

1

When the pilot piston is pressed down, it closes off the vent at the lower sealing element before the connection between 1 and 2 opens. In other words, the valve is free of overlap.

3

2

The force of the spring returns the piston to its normal position. The disk valve design permits small valves, and therefore relatively low actuating forces.

3

1

Poppet Valve with Plunger Actuation, Free of Overlap and with Reverse-Flow Feature


37

DETENT FOR HAND SLIDE

AIR SPRINGS

This valve is used to switch the compressed-air supply on and off by means of elastic seals. Its low profile design enables it to be easily fitted to other elements like distributors.

A so-called “ air-spring” can be fitted in place of the mechanical spring for returning the control spools of directional control valves to their normal position.

3

2

1

Hand-Slide Valve with Detent in both Switching Positions

This valve’s pilot piston is a differential piston which has two different piston-face areas. Pressure is applied to the smaller of the piston areas from inside the valve and is permanently subjected to the mains pressure through the branch passage from port 1. Pressure is applied on the larger piston area from the outside by the incoming compressed-air signal from pilot control 14. As compared to ordinary pilotcontrolled valves, it only behaves differently when the pilot control signal is applied to both ports 12 and 14 where the signal applied to the larger piston area dominates the switching position. The symbol for the differential piston valve, the side view with the smaller piston area is identified with a square. The arrow in the symbol represents the internal air actuation. It must be pointed out that when no air is applied to these valves, they assume as arbitrary, undefined position.

MECHANICAL DETENT Metal spool valves inherently have very low levels of sticking friction due to them not using seals. In order to ensure that the spool remains in position even when it is fitted vertically and when vibration and impacts occur, the valve is provided with a detent facility.

4

2

14

3

A spring-loaded ball engages in two grooves, and the force it exerts maintains the valve’s switching position.

5

1

Internal Air Spring The valve design below necessitates external control which can be connected using tubing and/or hose. Subplates are also available which already incorporate the required connections.

4

2

14

14

5

4

1

2

3

12

12

Pneumatic Impulse Valve with Internal Mechanical Detent

3

1

External Air Spring

5


PILOT CONTROL OF DIRECTIONAL CONTROL VALVES Pilot control of directional control valves becomes necessary when the actuating force required for the valve becomes excessive. This applies especially to poppet valves, and in particular to manually and mechanically controlled valves. In other words, pilot control is required when the valves must be frequently operated by hand or triggered by lightweight workpieces.

POSITIVE PILOT CONTROL (WITH APPLIED PRESSURE)

The figure below shows another positive pilot control of a 3/2 directional control valve by means of closing the nozzle with any object or workpiece. The compressed air flows out of the valve through the branch passage of very small diameter and the nozzle passage. It is also impossible for pressure on the left of the piston to build up. So this nozzle must be closed by an object or workpiece of some sort before the pressure can build up in left-hand control chamber. When the pressure has built up, it forces the pilot piston to the right against the spring and then the valve switches. Filters are fitted in the inlet lines to prevent the branch passage holes to be blocked by highly contaminated air.

The figure below shows a positive pilot control of a 3/2 directional control valve by means of closing the nozzle with an integrated ball actuator. There is a branch passage in the pilot piston through which the auxiliary air can enter the control chamber of a pilot piston having the same areas and spring return on the right side. It is impossible though for the pressure to build up in this control chamber because air can escape through the small nozzle. So the nozzle must be closed, whether with an object of some sort or by an integrated ball actuator, before the air pressure can build up in the control chamber and reverse the valve.

2

12

1

3

Integrated Ball-Actuated Valve using Positive Pilot Control

38

2

12

1

3

Pressure-Nozzle-Actuated Valve using Positive Pilot Control


39

NEGATIVE PILOT CONTROL (WITH PRESSURE RELEASE) In the case of solenoid-operated valves, pilot control also becomes necessary above a given size in order that the magnetic actuating forces (solenoid coil) can be kept to a low level. The level of electric power required for the coils is reduced and less heat is developed. The figure below shows a negative pilot control of a 3/2 directional control valve by means of solenoid control. Compressed air from port 1 reaches the valve seat of a solenoid-operated plunger through a branch passage. When the solenoid is energized, the plunger opens the valve seat and the auxiliary air applies pressure to the valve’s pilot piston thereby causing the spool to change the switching position and compress the spring. The pilot control valve is fitted with a manually or mechanically controlled valve which uses the auxiliary air from a branch passage to switch the main piston.

Solenoid Valves using Negative Pilot Control

The figure below shows another negative pilot control of a 3/2 directional control valve by means of opening the nozzle with a spring rod . There are two branch passages in the pilot piston, both control chambers are filled with auxiliary air. A spring on the left holds the pilot piston in the initial position. There is a very small opening in the control chamber which is sealed off by a spring rod. As soon as the spring rod is actuated from the outside the valve, it opens the valve vent hole and the air in the left-hand control chamber can escape and the air in the right-hand chamber can switch the valve.

2 12 12

2

3

1

Spring-Rod Actuated Valve using Negative Pilot Control

3

1

Solenoid Valves using Negative Pilot Control


FLOW-CONTROL VALVES SPEED REGULATION VALVES SPEED CONTROLLER VALVES An essential advantage inherent in pneumatic control engineering is the fact that it is an uncomplicated and inexpensive matter to adjust the working speed of cylinders and rotary actuators, as well as the speed of air motors. Cylinder piston rod speeds depend upon a number of factors: The speed restriction due to throttle valves and non-return valves with restriction Mechanical conditions, load and load changes Flow cross-sectional areas of actuators Diameters of hosing and tubing and the length involved Amount of pressure and pressure changes in the system. 



 



THROTTLE VALVES Throttle valves are members of the flow control family. Fitting an adjustable throttle valve to reduce the cross-sectional area enables the compressed-air flow rate to be adjusted, and with it the working speed.

ADJUSTABLE THROTTLE VALVE The variable throttle valve controls or limits the air flow by offering an adjustable restriction. The flow cross-sectional area in the throttle valve is changed by turning the throttling screw to adjust the position of the flow body. The air flow limit depends on the opening percentage and the pressure differential between the input and the output. At a constant opening percentage of the variable throttle valve, air flow increases if the pressure differential between the input and the output increases. Also, if the restriction decreases, the flow increases. The reduction in flow cross-sectional area has the same effect in both flow directions . The symbol for the throttle valve represents a restriction. An arrow passing obliquely through it indicates that the restriction is adjustable. Normally, speed-control of drive elements is only required in one direction. If speed control is stipulated in both directions, both speeds should be adjustable and independent of each other.

Throttle valves are connected into the line as close as possible to the element concerned. Fixed-set throttles and throttle valves are fitted to special-purpose subassemblies like pneumatic timers.

SCREW-INSERT THROTTLE VALVE

Typical Picture of an Adjustable Throttle Valve

Screw-insert throttle valves are screwed directly into the ports of the directional control valves. 1

2

1

2 Screw-Insert Throttle Valve

40

Adjustable Throttle Valve


41

FIXED THROTTLE VALVES A fixed throttle valve restricts air flow. The air flow going through a throttle valve depends on the opening percentage and the pressure differential between the input and the output of the valve. At a constant opening percentage of the throttle valve, air flow increases if the pressure differential between the input and the output increases. Throttling a Double-Acting Cylinder Non-Adjustable Throttle Valve

REGULATING THE SPEED OF PNEUMATIC CYLINDERS

When the pushbutton is pressed, pressure is applied to the piston area of the double-acting cylinder and its piston rod will extend at a speed slower than normal. But when the button is released, the piston rod will retract and will exhaust through the 5/2 directional control valve’s exhaust port but at a much slower speed as compared to the extending motion.

Throttling a Single-Acting Cylinder When the pushbutton is pressed, pressure is applied to the piston area of the single-acting cylinder and its piston rod will extend at a speed slower than normal. But when the button is released, the piston rod will retract due to the force of the spring and will exhaust through the 3/2 directional control valve’s exhaust port but at a much slower speed as compared to the extending motion.

Throttling a Double-Acting Cylinder using Screw-Insert Throttle Valves Also, if 5/2 directional control valves are used as actuators, screw-insert throttle valves can be fitted at the vent ports of the valves to adjust the cylinder speed in each direction independently.


42

One practical application of pilot-controlled non-return valves is with stopping controls of cylinder piston movements at any required position.

CHECK VALVE OR NON-RETURN VALVE A non-return valve allows air to flow in one direction and seals it off in the the opposite direction. Non-return valves are incorporated in speed controllers such as one-way flow-control valves and in seal fittings.

On the figure below, when the lever is actuated, the cylinder rod will extend slowly until it reaches its maximum extended position. Upon actuating the lever again, the cylinder will not retract until pressure is applied to the pilot-control port (21) to open the check valve in the other direction to exhaust the air through the lever-actuated valve. Note that the retracting motion of the piston rod can be halted at any given position whenever the pilot-control port (21) has no signal.

Typical Picture of a Non-Return Valve

1

2

Non-Return Valve

PILOT-CONTROLLED NON-RETURN VALVE The piloted operated check valve (open) behaves like the conventional check valve when there is no pressure applied at the pilot-control port (21). The only difference is that when the pilot pressure is positive (non-zero), the check valve is opened and the fluid can flow from port 2 to port 1. 21 2

1

Pilot-controlled Non-return Valve (Open) The piloted operated check valve (close) also behaves like the regular check valve. The only difference is that when the pilot pressure is positive (non-zero), the check valve is closed preventing the fluid from flowing in any direction. 21 2

1

Pilot-controlled Non-return Valve (Close)

On the figure below, when the normally-closed valve is actuated, pressure is released from the pilotcontrol port (21) allowing air to flow through the check valve slowly extending the cylinder. Removing this pilot signal will stop the cylinder extension at any desired position. Retracting the cylinder is function of the middle valve.


ONE-WAY FLOW-CONTROL VALVE THROTTLE CHECK VALVE NON-RETURN VALVE WITH RESTRICTION If 4/2 directional control valves are used as actuators, or when the cylinder and the 5/2 directional control valve acting as the actuator are too far apart, screw-insert throttle valves cannot be used for speed adjustments because the distance involved make precise control impossible. Throttle valves cannot be used either because in such cases, because otherwise the restriction is effective in both directions. Therefore, an assembly comprising of a throttle valve and a non-return valve connected in parallel is used.

43

In general, pneumatic throttles are used in pneumatic systems as cylinder speed control elements. When using flow-control valves as a speed control for an actuator, there are two control possibilities: 



mounted on the primary line (meter-in circuit), directly "before" the load mounted on the secondary line (meter-out circuit), directly "after" the load

Typical applications of one-way flow control valves are speed control of pneumatic cylinders in highly automated production systems in packaging, assembly, plastics and machine tool industries. Regulating Screw Mounting Screw

Mounting Screw

Because the non-return valve blocks the flow of air in one direction, while allowing it to flow in the other, the restrictor can adjust the actuator speed in only one direction. The variable non-return throttle valve controls air flow by offering an adjustable restriction. A restriction limits the air flow. At a constant opening percentage of the variable throttle valve, air flow increases if the pressure differential between the input and the output increases. Also, if the restriction decreases, the flow increases. The air flow limit going through the valve is dependent on the opening percentage and the pressure differential between the input and output. The pneumatic one-way flow control valve is also referred to as a pneumatic throttle valve. Throttle valves are used in many pneumatic systems to control air flow. There are two basic types of throttles - adjustable and non-adjustable, the adjustable version is the most commonly used. When using adjustable flow-control valves the user can adjust the effective throttling area to best suit the air flow needs of the individual application. The adjustable throttles are produced in various different constructive forms, for example: threaded throttle valves with or without silencers throttle valves (single)

Port 1

Housing

Port 2

Typical picture of a One-Way Flow-Control Valve Regulating Screw Housing

Spring

Port 2

Port 1 Check Valve






One-Way Flow-Control Valve


44

Air under Pressure

Outlet Port

Inlet Port

When the throttle of the one-way flow control valve is fully closed which means that the effective throttling area is equal to zero, there is no flow of compressed air from the inlet port of the valve towards the outlet port. The non-return valve in this case is closed too.

Inlet Port Non-Return Valve

Outlet Port

The reverse flow from outlet port to inlet port is not restricted. The air under pressure can flow freely through the incorporated non-return valve.

Regulating Screw

NON-ADJUSTABLE ONE-WAY FLOW-CONTROL VALVE Another version of the one-way flow-control valve is the screw-insert version which can be screwed directly into the cylinder ports. This design shows that the effective throttling area is not adjustable and is dependent only on the opposing forces of incoming pressure and the spring. Throttling is only effective from port 1 to port 2 and absolutely no air flow in the opposite direction.

Inlet Port

Outlet Port Effective Throttling Area regulating By turning the screw counterclockwise the throttle will open which means that the effective throttling area will be different from zero.

Now the compressed air flows under pressure through the throttle from the inlet towards the outlet port also known as port 1 to port 2. The flow rate can be controlled in a continuous manner by adjusting the effective area of the throttle. This is achieved by turning the regulating screw counterclockwise.

1

2

Non-Adjustable One-way Flow-control Valve


TYPES OF RESTRICTION OR THROTTLING WITH THROTTLE-CHECK VALVES

45

With single-acting cylinders, due to the inherent cushioning provided by the return spring, the inlet-air throttling method is usually applied.

When the non-return valves with restriction are used, a distinction is made between inlet-air throttling and exhaust-air throttling.

INLET-AIR THROTTLING USING METER-IN CIRCUIT Due to the fact that the compressed-air is compressible, uniform cylinder working movements are impossible to achieve when inlet-air throttling is employed. Inlet-Air Throttling of the Piston-Rod Extension The jerking (strong sudden movements) cylinder piston movements depend upon the cylinder diameter and the load fluctuations which the cylinder is subjected to.

EXHAUST-AIR THROTTLING USING METER-OUT CIRCUIT When this method is employed, the piston of the double-acting cylinder is virtually clamped between two air cushions. Full pressure is applied at the inlet-air side and the exhaust air is throttled. This leads to uniform cylinder movement. With double acting cylinders, therefore, exhaust-air throttling is always applied . The smallest cylinders, that is, the short-stroke cylinders are an exemption to this rule, because not enough pressure can build up in the inlet side of such cylinders.

Inlet-Air Throttling of the Piston-Rod Extension

Exhaust-Air Throttling of the Piston-Rod Extension


QUICK EXHAUST VALVE OR RAPID EXHAUST VALVE Quick exhaust valves are used if it is stipulated that the cylinder movements are to take place as quickly as possible . The quick exhaust valve is a member of the check valve family and is always fitted directly to the appropriate cylinder port. This component permits a maximum out-stroking piston speed by exhausting the cylinder directly at its port with a great flow capacity, instead of through the tube and valve.

46

When the compressed-air flows from the actuator in the direction of the cylinder, the quickexhaust valve’s sealing element ( rubber disc) closes the exhaust port (R). As a result, the compressed-air can flow via a relatively large cross-section with a negligible resistance through the valve and into the cylinder. If on the other hand, the compressed-air returns from the cylinder to the quick-exhaust valve, the valve’s sealing element closes the inlet port (A) . The volume of compressed-air can now escape rapidly through the large cross-section at the valve’s wide exhaust port (3).

Quick-exhaust valves are fitted whenever it is necessary to bypass line resistances, or when valves are concerned, the through-flow resistance. In combination with a given volume (provided for instance by an adequately dimensioned compressed-air reservoir), the quick-exhaust effect can be utilized for blowingout or rejecting workpieces.

Typical picture of a Quick-Exhaust Valve A

P

SILENCERS The sudden venting or exhaust of the cylinder chambers generates lots of noise especially to largevolume cylinders. As a result of regional noiseemission regulations, therefore, it is imperative that the quick-exhaust valves are fitted with silencers. The speed of the exhausted air is reduced sharply in the interior of the silencer with the result that the decompression noise is also reduced. Silencers are used to diminish the noise and the carry over of particles produced by air exhausts on the various pneumatic components. They are installed at the exhaust port of most valves.

R Typical picture of a Silencer

Cross-sectional view of the component’s construction A P

R

Quick-Exhaust Valve

Some models have a variable throttle that can be adjusted by a screw. The restriction at this port will control the air flow going through the silencer so that it can slow down the actuator from which the air escapes .


47

A

SHUTTLE VALVES OR “OR” VALVES

E1

This is a three-ported valve with two signal-pressure inlets (E 1 and E2) and one outlet (A). The outlet is connected to either signal input. If only one input is pressurized, the shuttle prevents the signal pressure escaping through the exhausted signal port on the opposite side.

E2 Shuttle Valve

Being as the shuttle valve, it has no venting facility of its own and venting must take place though the signal element as shown in the figure below.

A shuttle valve is always employed when two pneumatic signals are to be interlinked with each other. Since a signal is always present at the outlet when pressure is applied at either inlet, this valve is regarded as a Logical-OR-Valve. If there is a signal present at both inlets, the sealing element assumes an undefined position, but air is nevertheless able to flow to the outlet. This valve incorporates a sealing element or a ball which is fitted so that when a signal is applied at one of the two inlets, the other inlet is closed and no air can escape.

OR FUNCTION BLOCKS

E1

A3

A2

A1

If the two applied signal pressures are unequal, it is always the higher pressure which appears at the outlet.

E2

E3

E5

E4

E6

OR-Function Blocks for Multiple Logical Operations A3 Typical picture of a Shuttle Valve A

A2 A1

E1

E2 E1

E2

E3

E4

OR-Operation using 4 Signal Inputs Cross-sectional view of the component’s construction


48

PRESSURE-SHUTTLE VALVES OR “AND” VALVES The pressure-shuttle valve is also used for logical operations using pneumatic signals. The valve has two inlets (E 1 and E2) and an outlet (A). Since a signal shall only be present at the outlet until a signal is present at both inlets, this valve is regarded as a Logical-AND-Valve. The pressure-shuttle valve in itself is not to be regarded as a safety-function valve, but only as a logical-function valve in the appropriated sub-assemblies. If the two applied signal pressures are unequal, it is always the lower pressure which appears at the outlet.

Applications involving pressure fluctuations and low signal pressures such as when long lines are used, the equivalent circuit below is used where the weaker signal is being fed to E 1. A 2

12

1

3

E1

E2 Equivalent Circuit with Directional Control Valve Typical picture of a Pressure Shuttle Valve

AND FUNCTION BLOCKS A1

A3

A2

A

E1

E2

E1

E2

E3

E4

E5

E6

AND-Function Blocks for Multiple Logical Operations A2

Cross-sectional view of the component’s construction A1

A3

A1 E1

E2

Pressure Shuttle Valve

E1

E2

E3

E4

AND-Operation using 4 Signal Inputs


49

GATE VALVES OR SHUT OFF VALVES

STOP-CONTROL VALVES USED IN LOCKING UNITS

It acts as the pneumatic On-Off Switch of pneumatic installations such as the pneumatic power supply system and in compound network lines where isolation of branch lines is needed.

Locking units are mechanical/pneumatic solutions for stopping cylinder movements by clamping or releasing the piston rods in any required position. The clamping force, therefore, must exceed the maximum output force of the cylinder.

However, the locking units are not provided with a braking function for the complete stopping action of the cylinders because the locking force is generated by a spring or generated pneumatically. But the 5/3-way directional control valve with a special-center position is used for this purpose.

Typical picture of a Shut-Off Valve

The shut-off valves below can isolate 2 distinct lines in a pneumatic circuit.

Shut-Off Valve Normally-Closed with Two Orifices

Shut-Off Valve Normally-Open with Two Orifices

Typical picture of a 5/3-way Directional-Control Valve

5/3-way Directional-Control Valve

The shut-off valves below can isolate 3 distinct lines in a pneumatic circuit.

Shut-Off Valve Normally-Closed with Three Orifices

Shut-Off Valve Normally Open with Three Orifices

Locking Unit with a 5/3-way Directional-Control Valve


50

PRESSURE-CONTROL VALVES

PRESSURE-RELIEF VALVE

The members of the family of pressurecontrol valves are designed to control the level of pressure in the system. Some reduce and regulate the pressure levels and while others sense the level of pressure at certain points in the system to relieve excess pressure, or just to allow air flow through them or trigger electrical functions when certain levels of pressure has been detected.

When the pressure in the system increases above a preset value, the pressure relief valve opens and lets air flow to atmosphere . This component acts only in case of an emergency, to bring down the pressure to its set value. Some models are adjustable while others are sealed so that non authorized personnel may not adjust them. These sealed pressure relief valves are usually fitted on air receivers.

PRESSURE REGULATOR The pressure regulator maintains the pressure constant at its output, even if the input pressure varies. An adjustment knob will allow users to modify the output pressure of the regulator.

Typical picture of a Pressure Relief Valve

Pressure Relief Valve, Adjustable

Typical picture of a Pressure Regulator

Pressure Relief Valve Non-Adjustable

Piloted Pressure Relief Valve

PRESSURE SWITCH / SENSOR

Pressure Regulator, Adjustable, Relieving type

Pressure Regulator, Relieving type

Pressure Regulator, Adjustable, Non-Relieving type

Pressure Regulator, Non-Relieving type

This sensor is switch activated once the pneumatic input pressure at its connection port is equal to or greater than its pressure setting . The pressure setting is adjusted by a screw that will compress a spring placed in the sensor.

Typical picture of a Pressure Switch

Piloted Pressure Regulator

Pressure Switch


SEQUENCE VALVE

PNEUMATIC ACCESSORIES

The sequence valve is usually located on the supply line of a cylinder or on a branch of a pneumatic circuit that is isolated from the main circuit. When the pressure in the main circuit reaches the set pressure of the sequence valve, it opens and lets air flow to the cylinder or to the branch of the circuit .

AIR DRYER The air dryer is usually installed at the output of compressors to extract the moisture contained in compressed air, so that it does not damage pneumatic components. Air dryers function by refrigeration or chemical action. In both cases, the moisture transforms into condensate and is extracted with a separator.

Sequence Valves, Adjustable, With Pressure Relief The sequence valve without check valve allows air flow in only one direction. Its use is therefore limited to places where air always circulates in the same direction. If the air has to circulate in both directions, a sequence valve with a check valve must be used.

Sequence Valves, With Pressure Relief

Air Dryers

FILTERS Filters purify the air by blocking the solid contaminants. They are available in various filtration grains and are used in various places in a pneumatic circuit. Where air moisture condensation may form, a filter with an automatic drain must be installed. The condensate accumulates in the filter's bowl up to a certain level. A floater then activates the opening of the filter drain and the condensate is expelled. The drain closes when the bowl is empty.

Sequence Valves, With Check Valve

AIR-SERVICE UNIT This component combines filtration, pressure regulation and lubrication functions.

Typical Picture of a Filter

Filter

Typical picture of an Air-Service Unit

Air-service Unit

51


Water Trap, Manual

Filter with Water Trap, Automatic

Water Trap, with Automatic Drain


52

LUBRICATOR

SILENCER

Almost all pneumatic components need to be lubricated to work correctly and have a satisfactory life span. The best way to achieve this is to install a lubricator which will allow constant and automatic lubrication to the correct level.

Silencers are used to diminish the noise and the carry over of particles produced by air exhausts on the various pneumatic components. They are installed at the exhaust port of most valves.

Oil is atomized into the compressed air flow and the resulting oil mist is then transported by the air flow to the component requiring it. It is important to try and install the lubricator as close as possible to the component/system that requires lubrication so that oil mist condensation is reduced to a minimum.

Typical picture of a Silencer Some models have a variable throttle that can be adjusted by a screw. The restriction at this port will control the air flow going through the silencer so that it can slow down the actuator from which the air escapes .

Silencer

Silencer with Throttle Valve

PRESSURE INDICATOR

Typical Picture of a Lubricator

A pressure indicator has a window in which an indicator changes color according to the presence or the absence of pressure. A very light pressure is sufficient to activate the pressure indicator.

Lubricator

COOLER A cooler is used when you need to lower the temperature of compressed air. A cooler is usually located at the output of a compressor, before the conditioning units. Typical Picture of a Pressure Indicator Green

Cooler

Pressure Indicator


53

DIFFERENTIAL PRESSURE GAUGE

T-CONNECTORS

The differential pressure gauge makes it possible to measure the relative pressure between 2 points of a pneumatic system.

T-connectors allow interconnection between three pneumatic hoses, giving two outputs for one input of the connector.

0

Differential Pressure Gauge Typical Picture of a T-Connector

COUPLER PNEUMATIC DISTRIBUTORS The coupler is used to easily plug or unplug pneumatic components. It does not have a check valve. This allows better air flow since the restriction caused by this coupler is less than the one offered by the coupler with check valve. However, there is a potential hazard inherent with exhausting large volumes of air to atmosphere in an uncontrolled manner as the coupler is unplugged, especially through a flexible hose.

Coupler or Quick Release Coupling Uncoupled, Line open

Pneumatic distributors allow the pneumatic supply energy from the pneumatic power supply to be distributed to the pneumatic installation by providing multiple output supply ports.

Coupler with Check Valve Uncoupled, Line open Typical Picture of a Pneumatic Distributor

Quick Release Coupling, Coupled

Quick Release Coupling, with Mechanically-opened Check Valve

PLUGS Plugs are used to block fluid flow. The two plugs on the left are used to plug distributors' ports. The plug on the right is used to prevent fluid to flow in a pressure line.

Plugs


54

SUB-ASSEMBLIES When pneumatic drive elements are combined with mechanical devices or with valves and other elements to form a unit, and are installed and used in this form, one refers to such units as sub-assemblies. They are to drawn inside a square to stipulate that they are subassembly units. Such examples are:    

Guide units Feed units Force converters Clamping units

Typical Picture of a Pneumatic Timer, Sub-Assembly Type

And even when several different types of valves are combined in a single block, they are also referred to as sub-assemblies.       

Non-return valve with restriction Air-Service Unit Sequence Valve with Check Valve Silencer with Throttle Valve Coupler with Check Valve Pneumatic Timers Two-hand control block

PNEUMATIC TIMERS

Z

P/R A


In the case of process-oriented sequential controls, time-oriented switching elements in the form of purely pneumatic timers are used in the form of subassemblies or pneumatic-mechanical timers.

PNEUMATIC TIMER, SUB-ASSEMBLY TYPE Depending on the timer size, the delay time of pneumatic timers is infinitely adjustable from 0.2 to 30 seconds. The setting accuracy of about ± 10 % is relatively low and depends u[on a number of factors but is sufficient though for pneumatic applications. A pneumatic timer subassembly comprises the following elements: 





3/2 way DCV, with reverse-flow feature, with rapid switching and without overlap Non-return valve with restriction, finely adjustable Compressed-air Reservoir

R/P

A

Z

PR

Pneumatic Timer, Sub-Assembly Type


55

DELAYED SWITCH-ON TIMERS OR ON-DELAY TIMERS

DELAYED SWITCH-OFF TIMERS OR OFF-DELAY TIMERS

If a continuous signal is applied to pilotcontrol port (Z), air flows into the reservoir through the throttle point of the non-return valve with restriction.

Pneumatic timers are also used when an applied signal is only to be effective for a given period of time, after which it is to be converted as a pulse.

The pneumatic valve switches abruptly as soon as the required pilot pressure has built up in the reservoir, and then the compressed air flows from the inlet port (P) to the outlet port (A). The delay period is determined primarily by the throttle setting . In the case of miniature timers, the delay time can result from adjusting the timer’s volume.

When the control signal at pilot-control port (Z) is vented, the pressure in the reservoir can escape very rapidly through the non-return valve which is open in this direction, and then the valve switches back again to its original position. A

Z

P

R

Such sub-assemblies differ from the timers used for normal time-delay insofar as the integral valve is in the through-flow normal position. With these timer versions, the continuous signal which is to be switched off (due to an actuated position switch) is applied simultaneously to inlet port (P) and control-pilot port (Z). The compressed air can now flow immediately to the outlet port (A). The passage through the throttle results in the valve switch-over being delayed. After a given delay, the valve switches and the signal at the output is switched off. It remains switched off as long as the continuous signal is at ports P and Z. A

Z

P

R

Time-delayed Signal Switch-On

Time-delayed Signal Switch-Off

When the ON delay timer's input is pressurized, the output is pressurized with this same pressure but only after the specified delay. The output pressure stops immediately when the input pressure is stopped.

When the OFF delay timer's input is pressurized, the output is simultaneously pressurized with the same pressure level. The output pressure is maintained only during the preset delay.

Input Pressure (P)

Input Pressure (R)

Output Pressure (A)

Output Pressure (A)

T The output pressure is delayed by the specified timer amount (T).

T The output pressure is maintained only within the specified timer amount (T).


56

A

Input Pressure (P)

P

Z

R

Output Pressure (A) T The output pressure is delayed by the specified timer amount (T).

Time-delayed Signal Switch-Off

PNEUMATIC-MECHANICAL TIMER When the OFF delay timer's input is pressurized, the output is continuously pressurized and maintained with the same pressure level but only within the preset delay. When the input pressure is stopped, the output pressure returns immediately.

If the accuracy of pneumatic timers is inadequate because for instance if pressure fluctuations are present or if very long delay time is required , pneumatic-mechanical timers are used. These so-called pre-setting timers feature time delay settings of 0.3 second to 100 hours with an accuracy of about ± 2 %.

Input Pressure (R) Output Pressure (A) T The output pressure is maintained only within the specified timer amount (T).

The analog time-to-go is displayed by means of the knob’s red pointer. The required time is set using the white knob itself (white pointer). The start of the pneumatic-mechanical rotor system is triggered by a pneumatic signal applied at port a, X. As soon as the time has expired, a 3/2 DCV inside the unit switches, and a 200 ms pneumatic pulse is outputted from port A.

A a, X t Z

P

R

Time-delayed Signal Switch-Off When the OFF delay timer's input is pressurized, the output is almost simultaneously pressurized with the same pressure level. When the input pressure is stopped, the output pressure is maintained during the preset delay.


PNEUMATIC TWO-HAND CONTROL BLOCK Stringent safety regulations apply when controls are concerned in which operators can reach into devices or installations and in doing so, run the danger of injury. As a mandatory safety requirement, two manually-operated pushbuttons with recessed knobs must be fitted to the installation in such a manner that it is impossible for both knobs to be depressed using only one hand or arm.

E2

R

P

If, within a period of 0.5 second , there is only a signal at E1, valve 2 (bottom) switches, and the compressed-air reservoir is slowly filled via compressedair port (P), valve 2, and the non-return valve with restriction. The same thing happens, without one of the valves switching, when a signal is only present at E 2 within the 0.5 sec period. The pressure in the reservoir has increased to such an extent within the 0.5 second that a blocking signal appears at the right-hand pilot port and prevents valve 1 (top) from switching . And so it is impossible for a signal to reach the output port (A). Even if the second push-button is pressed after the 0.5 second period has elapsed, valve 1 (top) still cannot switch because the blocking signal still blocks it. This is due to the fact that the first signal to arrive will dominate.

A

E1

57

A further safety function is provided by the spring actuation of the right-hand switching position.

S

If both signals do arrive within the 0.5 second period (by virtue of the logical-AND-operation of E 1 and E2), first of all, a signal reaches the left-hand pilot port of valve 1 and valve 2 switches and outlet A is pressurized.

Circuit Diagram of the Pneumatic Two-Hand Control Block A

A S

S

E1

R

E2

P

E1

R

E2

P

Pneumatic Two-Hand Control Block The two-hand control is a normally closed shut-off valve. The air can only flow through when both controls are pressed simultaneously or one after the other in less than half a second.

Two-Hand Safety Control using a Pneumatic Two-Hand Control Block


VACUUM ENGINEERING Vacuum engineering is employed in applications where transportation and stopping functions must be performed with very great care. With holding forces of up to 350 Newton, flat, slanting or round workpieces with rough, smooth or uneven surfaces can be safely transported. Suction Cup Diameter In millimeter 10 20 40 60 95

The operating pressure is applied at input port (P). The reduction in area in a jet nozzle causes the compressed air to be accelerated. Vacuum is then generated in the restricted space at the vacuum port (V) where the suction cups are connected. The compressed air escapes through the vent port (R). The operating pressures should be 3 to 7 bars while the air consumption depends upon the vacuum.

Holding Force In Newton 3, 6 14, 3 57, 1 128, 5 350

Negative pressure is the working medium employed by this equipment technology. Vacuum is given in PE-Bar or in %Vacuum. The ideal working (negative) pressure is between -0.8 and -0.6 bar that is, 80% to 60% vacuum.

58

Typical picture of a Vacuum Ejector

R

P

Two methods are used to generate negative pressure, Mechanical Pumps or Vacuum Ejectors. V

MECHANICAL PUMPS They are used when a large number of suction cups are to be operated simultaneously, or a range of applications must be supplied from a central point.

VACUUM EJECTORS/GENERATORS On the other hand, Ejectors can be employed to generate vacuum. They are suited for direct operation of up to as many as 3 suction cups. The vacuum generator uses the Venturi effect to create a vacuum. The air going through the Venturi is accelerated because of the decreasing diameter in the Venturi. As the air flow increases, pressure decreases. The vacuum cups function with this pressure drop.


Vacuum Generator


VACUUM / SUCTION CUP The vacuum/suction cups are the working elements employed in vacuum engineering. They are handling devices for objects presenting a flat surface. They are either of the Flat-type or the Telescopic-type.

59

Suction cups are employed to hold workpieces and are suitable for the mechanical transportation and fixation of small to medium-sized objects. Cups can be used in numbers to obtain a greater lifting force.

Simple Vacuum Set-up

Flat-type Suction Cups % Vacuum

Telescopic-type Suction Cups

80 60 40 20

1

2

3 PE (Bar)

4

5

6

Supply Pressure and Vacuum Percentage Relationship Typical picture of a Vacuum Cups Liter 4 Vacuum / Suction Cup By creating a vacuum between the cup and the surface of the object, you have a suction force that can hold the object. The suction cup holds the workpiece when the surrounding pressure is higher than that between the suction cup and the surface of the workpiece with which it is in contact. The suction force obtained is the product of negative pressure (vacuum) and the surface of the cup. The level of suction force is a function of the available vacuum, the effective suction area, and the number of suction cups .

3 2 1 10

20

30 40 50 % Vacuum

60

70

80

Air Consumption (Liters) required to evacuate a volume of 1 Liter


PNEUMATIC SIGNAL TYPES AND CONTROL TYPES In accordance with DIN 19226, controls are classified according to: 1.

The way the information is represented Analog Digital Binary   

2.

The type of sequence concerned Logical control Sequential control Sequential  Time-oriented Control  Process-oriented Sequential Control  

3.

The type of signal processing used Command-variable control Holding-element control Programmed control  Time-scheduled/dependent control  Position-scheduled /dependent control   

TYPES OF CONTROL

LOGICAL CONTROL

SEQUENTIAL CONTROL

Command-Variable Control

Programmed Control

Holding-Element Control

TIME-ORIENTED SEQUENTIAL CONTROL

PROCESS-ORIENTED SEQUENTIAL CONTROL

Time-Scheduled Control

Position-Scheduled Control

60


61


62

POSITION-DEPENDENT CONTROLS When an actuator performs a movement (for instance, the cylinder’s piston rod moves out), and a second operation is triggered depending upon the rod’s movement (which is monitored and signaled back), this is referred to as Position-dependence. Position switches or Limit switches are used to register and signal back such movements. For the most part, 3/2 directional control valves are used as position switches in pneumatic engineering. These are mechanicallycontrolled valves with spring return. One prerequisite for the use of such valves is that only low actuating forces should be needed.

Plunger

Note that the actuation of a position switch by means of an operating cam (machine part that transfers motion) on the piston rod is symbolized by a triangle. The position of the mounting or the positionswitch actuation is symbolized by a dash. S1

S2

Ball Representation of Roller with Idle Return Spring Rod

Note that the direction in which the actuation takes place is indicated by an arrow. S1

Pressure Nozzle No Mechanical Contact S1

Roller

S1

Roller with Idle Return

Pressure Nozzles

Roller

Mechanical Contact

Roller with Free Return

Mechanical Contact When Extending

Mechanical Contact When Retracting


REPRESENTATION OF PNEUMATIC CIRCUIT DIAGRAMS The arrangement of the graphical symbols in a circuit diagram should correspond to the control loop schematic diagram. 









The signal flow should take place from bottom to top. The sequence of cylinder operations should be from left to right. The presentation of energy supply should always take place in the same circuit diagram. However, for simplicity the energy supply can be shown separately by means of the symbol for the pneumatic pressure source. The elements are shown in the pressureless mode except when they are meant to have an initially pressurized condition. If the pistons of double-acting cylinders are extended in their initial position, they are to be drawn in the extended position.

DESIGNATION OF PNEUMATIC ELEMENTS IN CIRCUIT DIAGRAMS There is no concrete standardization applicable to pneumatic circuit diagrams. Among the possible designation systems are: 

 

Letter or number systems, or a combination of the two. Simple numbering of the elements Group numbering according to the control loop schematic diagram and the signal flow

Drive elements are designated from left to right using Z1, Z2, Z3 , etc. or by A, B, C , etc. Signaling elements, control elements and actuators are identified by two digits separated by a period. The digit to the left of the period identifies the cylinder or the control loop allocation, and the digit to the right is the running number according to the signal flow. Starting from the bottom row, the units are numbered from right to left, e.g. 1.1, 1.2, 1.3 etc.

63

Energy supplies are allocated a zero to the left of the period. The numbers to the right of the period are allocated according to the energy flow, e.g. 0.1, 0.2, 0.3 , etc.

The elements in between the actuator and the drive element such as the flow-control valves can be designated using the same system as with the signaling elements, control elements and actuators.


SEQUENTIAL REPRESENTATION OF MOTIONS As soon as there are more than two drive elements in a control, it becomes imperative that the control sequence is represented of diagrams.

3.

SHORTHAND NOTATION

Z1 Z2 Z1 Z2

Z1

FUNCTION STATE DIAGRAMS A function state diagram is a form of a representation of a sequential control in pneumatic systems that show the sequence and the position of the drive elements. This form of representation permits the straight forward representation of all drive elements of a control loop.

1.

64

A B A B

Z2

Z1

Z2

Z1

Z1

Z2

A

Z2

B

A

B

B

A

A

B

TABULAR REPRESENTATION

STEP

CYLINDER 1

CYLINDER 2

1

Extend

-

2

-

Extend

3

Retract

-

4

-

Retract

4.

POSITION-SEQUENCE DIAGRAM

The functional sequence of one or more drive elements together with the respective components can be shown using two coordinates. POSITION-SEQUENCE DIAGRAM Step 1 2 Cylinder 1 (Z1)

3

4=1

2 1

2.

POINTER REPRESENTATION Cylinder 2 (Z2)

2 1

Z1 Z2 Z1 Z2

Z1

Z2

Z1

Z2 The POSITION is shown in the ordinate while the STEP is shown in the abscissa. 5.

A B A B

A

B

A

B

POSITION-TIME DIAGRAM

POSITION-TIME DIAGRAM Time(s) 0 1 Cylinder 1 (Z1)

2 1

Cylinder 2 (Z2)

2 1

2

3 4

5

6 7

8

9

10 11


65

The POSITION is shown in the ordinate while the TIME is shown in the abscissa. For both position-sequence and the position-time diagrams: 









The actuator movement is indicated by the sloping action line on the grid. The standstill state is indicated by the horizontal action line on the grid. Either diagram has their drive elements stacked on top of each other. The ordinate representing the position of the drive element in its retracted state is termed number 1 while the extended state is termed number 2. In the control sequence, the position of the drive elements for the last step (END) always corresponds to the first step (START).

Note: 









14 14

0

12

12

FUNCTION CHART



If the interplay between the drive elements and the actuators and controlling elements is to be dictated, the representation is designated as the function chart. As per VDI 3260, the function chart permits not only the straight-forward representation of all the components of a control loop, but also the information on the job, function and interplay of the elements concerned.

t

Mechanicallycontrolled Signaling Elements

Time-dependent Signaling Elements Muscular Power Actuation

Signal Line

Actuated Normal Position

The change of state of controlling elements and actuators are represented by a vertical step line.

2

2

1

1







FUNCTION CHART SYMBOLS

A component’s normal position is represented by a thin function line, while the remaining position by a thick function line. A signal line is used to indicate the dependence of the drive elements upon the signaling elements and actuators, while the arrow shows the direction of action. Signaling elements actuated by muscular power are represented by signals inside a circle . Mechanically-controlled signaling elements are represented by a heavy dot. Time-dependent and pressure-dependent signaling elements are represented by a special symbol inside a square.

The movements of drive elements are represented by a sloping function line. Different drive element speeds are indicted by the different function line slope angles. The drive element’s standstill state is represented by a horizontal function line.


GENERATING A FUNCTION CHART

Time(s) Step

COMPONENTS

1

Designation

Identification

State S3

Cylinder (A)

A

2 1

Directional control valve ( V1)

1.3

14 12

S0

2

S2

3

4

5

6= 1

S1

S4

Cylinder (A)

B

2 1

Directional control valve ( V2)

1.6

14 12

Directional control valve ( S0)

1.1

12 10


1.7

12 10


1.5

12 10


1.2

12 10


1.4

12 10

S3

66

PNEUMATICS Student Cop

Recommend Documents