Pneumatics

TVS TRAINING & SERVICES SERVICES LTD Vanagaram, Chennai – 600 095

MODULE: ELECTRO PNEUMATICS

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TVS TRAINING & SERVICES SERVICES LTD Vanagaram, Chennai – 600 095 INTRODUCTION Pneuma means ‘Compressed air’. Pneumatic systems use compressed air to transmit and control power. Pneumatic cylinders convert pneumatic energy into mechanical energy. Advantages 

Air is available everywhere in unlimited qu antities.



Air can be easily transported in pipelines over large distances.



Compressed air can be stored in a reservoir and removed as required.



Compressed air is insensitive to temperature fluctuations.



Compressed air offers minimal risk of explosion or fire.



The operating components are of simple construction and therefore relatively inexpensive.



Higher working speeds can be achieved.

Disadvantages o

Compressed air requires good preparation.

o

It is not always possible to achieve uniform and constant piston speed with compressed air.

o

Noisy operation.

o

This system is economical up to a certain force requirement.

Applications 1. Material handling o

Clamping

o

Shifting

o

Positioning

o

Orienting

2. Machining and working operations o

Drilling

o

Turning

o

Milling

o

Sawing

o

Finishing

o

Forming

o

Quality control

3. General applications o

Packaging

o

Feeding

o

Metering

2

TVS TRAINING & SERVICES SERVICES LTD Vanagaram, Chennai – 600 095

CIRCUIT STRUCTURE & ISO SYMBOLS AND STANDARDS Pneumatic circuit structure The structure of the circuit diagram should correspond to the control chain, whereby the signal flow is represented from the bottom to the top. Simplified or detailed symbols may be used for the representation of the circuit diagram.

Signal flow The various levels form a control path for signal flow from the signal (input) side to the work (output) side.

System structure The primary levels in a pneumatic system are: ☻

Energy supply

☻

Input elements

☻

Processing elements

☻

Actuating devices

ISO symbols The development of pneumatic systems is assisted by a uniform approach to the representation of the elements and the circuits. The symbols used for the individual elements must display the following characteristics: 3

TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095

o

Function

o

Actuation and return actuation methods

o

Number of connections

o

Number of switching positions

o

General operating principle

o

Simplified representation of the flow path

The symbols used in pneumatics are standardized by the code DIN ISO 1219.

Symbols used in energy conversion and preparation

Supply Compressor

with fixed capacity

Air receiver and ‘T’ junction

Service equipment Filter

separation and filtration of particles

Water separator

partial water removal

Lubricator

metered quantities of oil passed to the air stream

Pressure regulator

relieving type – vent hole for excess upstream pressure – adjustable

Combined symbols Air service unit

Filter, Regulator, Gauge, Lubricator.

Simplified air service unit

Pressure source

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Directional control valves: ports and positions (ways)

2/2 – way directional valve

3/2 – way directional valve Normally closed

3/2 - way directional valve Normally open



5/3 – way directional valve Mid position closed

Method of actuation Mechanical General manual operation

Push button

Lever operated

Detent lever operated

Foot pedal

Roller operated

5


Plunger operated

Spring return

Spring centered

Idle return, roller

Pneumatic Direct pneumatic actuation

Indirect pneumatic actuation (piloted)

Electrical Single solenoid operation

Double solenoid operation

Combined Double solenoid and pilot operation With manual override

Non-return valves and derivatives

Check valve

Spring loaded check valve

Shuttle valve “OR” function

Two pressure valve “AND” function

Quick exhaust valve

Flow control valves

Flow control valve adjustable

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One – way flow control valve

Pressure valves

Adjustable pressure regulating valve, Non – relieving type

Adjustable pressure regulating valve, Relieving type (overloads are vented)

Sequence valve combination

Linear actuators

Single acting cylinder

Double acting cylinder

Double acting cylinder with double ended piston rod

Double acting cylinder with non-adjustable cushioning in one direction

Double acting cylinder with single adjustable cushioning

Double acting cylinder with adjustable cushioning at both ends

Linear drive with magnetic coupling

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Rotary actuators

Air motor, rotation in one direction fixed capacity

Air motor, rotation in one direction variable capacity

Air motor, rotation in both directions variable capacity

Rotary actuator limited travel in both directions

Auxiliary symbols

Exhaust port

Exhaust port with threaded connection

Silencer

Line connection (fixed)

Crossing lines (not connected)

Pressure gauge

Visual indicator

Signal flow (electrical)

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Electropneumatic symbols

Switches and relay contacts

Manual actuation

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Relay and actuator coil symbols

Relay coil and contact symbols

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Mechanical and electrical actuation

COMPRESSED AIR GENERATION & DISTRIBUTION Compressed air generation and supply Air preparation For the continuing performance of control systems and working elements it is necessary to guarantee that the air supply is: 

clean



dry and



at the required pressure

If these conditions are not fulfilled, then short to medium term degeneration of the system will be accelerated. The effect is downtime on the machinery in addition to increased costs for repair or replacement of parts. The equipment to be considered in the generation and preparation of air include: 

Inlet filter



Air compressor



Air reservoir



Air dryer



Air filter with water separator



Pressure regulator



Air lubricator as required



Drainage points

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Pneumatic components are designed for a maximum operating pressure of 800 to 1000 kPa (8 – 10 bar). Practical experience has shown that approximately 600 kPa (6 bar) should be used for economic operation. The compressor’s system should provide at least 650 to 700 kPa (6.5 to 7 bar) for a desired operating pressure level of 600 kPa (6 bar).

Air compressors The various types of compressor are:

Selection of compressors The selection of compressor is based on: 

Quantity of air



Pressure



Quality and cleanliness of the air required.

The optimum ranges of pressures for reciprocating compressors are approximately : Up to 400 kPa

(4 bar)

single stage

Up to 1500 kPa

(15 bar) double stage

Over 1500 kPa

(> 15 bar)

treble or multi stage

Diaphragm compressor is used where oil is to be excluded from the air supply, for example in the food, pharmaceutical and chemical industries. Here there is no need for lubrication in the compression area. Rotary piston compressors use rotating members to compress and increase the pressure of the air. They are smooth in operation but the compression is not as high as with multistage reciprocating compressors. Flow compressors produce large volumes of air at small increase in stage pressure. The air is accelerated by the blades of the compressor but there is only a small increase in pressure of about 1.2 times the inlet pressure per stage.

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Reservoirs A reservoir compensates the pressure fluctuations when the compressed air is taken from the system. If the pressure in the reservoir drops below a certain value, the compressor will compensate until the set higher value is reached again. This has the advantage that the compressor does not need to operate continuously.

The large surface area of the reservoir cools the air. Thus, a portion of the moisture in the air is separated directly from the reservoir as water, which has to be regularly drained via a drain cock.

The size of a compressed air reservoir depends on the : Delivery volume of the compressor Air consumption for the applications Type of compressor cycle regulation Permissible pressure drop in the supply network.

AIR DRYERS Air dryers reduce the moisture content to a level, which suits the application, and the elements used. Water produces a hardening of seals, corrosion and the washing-out of the original lubrication of cylinders. Oil and water may cause seals and diaphragms to swell. In paint-spraying plants, water and dust cause contamination, poor paint adhesion and the formation of blisters. In the food, pharmaceutical and chemical industries, oil, dirt, bacteria and germs destroy the storage properties of products. There are three methods of reducing the moisture content in air: 

Low temperature drying



Adsorption drying



Absorption drying

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Air service equipment It is a combination of : 

Compressed air filter



Compressed air regulator and gauge



Compressed air lubricator

Air service equipment is also termed as FRL unit.

Filter Filter removes the dust particles. The compressed air passes through the filter from left to right and is fed through a baffle plate in the filter bowl. The effect of the baffle plate is that the air is caused to rotate, and the heavier dust particles and water droplets are spun by centrifugal force against the inner wall of the filter bowl. The air, which has pre-cleaned in this way, then passes through the filter element, which filters out the smaller dirt particles. The filte The degree of separation depends on the pore size of the filter element used. Guide line for maintenance: 

Filter cartridge should be changed or cleaned with kerosene or trichloroethylene or other cleaning mediums. But no chemicals like CTC, acetone are to be used for cleaning plastic parts.



The condensate level must be checked regularly, as the height specified on the sight glass must not be exceeded.



Drain off the accumulated water and other foreign particles from the filter bowl.

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Regulator Regulators ensure a constant supply pressure and also regulate the pressure of the air.

Basically there are two types: o

Relieving type

o

Non – relieving type

Relieving type:

Non – relieving type:

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Setting and adjusting: The pressure regulator can be adjusted between the limits of zero and the supply pressure of the compressor network. The adjustment to a higher pressure is achieved by increasing spring compression. When reducing pressure settings, it is necessary to relieve the pressure well below the limit required to relieve the air from the vent and then increase the pressure up to the lower limit required.

Guide line for maintenance: 

Check if the supply of the pressure air is steady or not. Pressure limits should be tested.



Look for an external damage to the regulator.

Lubricator: Lubricators are used to lubricate the air. For power components it may be necessary to lubricate the air. But as a rule the compressed air should be free of oil. Fig. shows an air lubricator:

The compressed air passing through the lubricator causes a pressure drop between the oil reservoir and the upper part of the lubricator. The pressure difference is sufficient to force the oil upwards through a via duct where it then drips into a nozzle which can be seen through an inspection glass. Here the oil is atomized and taken up by the air stream to a greater or lesser extent.

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Problems that occur with excessive lubrication: o

Malfunctioning of the components

o

Oil mist pollution of the environment

o

Gumming-up of parts occurs

o

Difficulties in adjusting the lubricator correctly

Guide line for maintenance: 

Check the oil level in the oil sight glass and top up, if necessary, to the level indicated.



Lubricator bowl must not be cleaned with trichloroethylene.



Only mineral oils can be used for the lubricator.



Inspect the colour of the oil in the bowl and if the colour turns grayish, replace the oil.

DIRECTIONAL CONTROL VALVES These valves influence the path taken by an air stream. These valves: 

Allows the passage of air directing it to particular airlines



Canceling the air signals as required by blocking the passage



Relieve the air through the exhaust port

Based on their design the valves are classified as: o

o

Poppet valves 

Ball seat valves



Disc seat valves

Slide valves 

Longitudinal slide valve



Longitudinal flat slide valve



Plate slide valve

Poppet valve uses balls, discs, plates or cones for opening or closing the connections. Slide valve uses spool slides, spool flat slides or sliding disc valves for linking the connections together or closed. Also based on the number of ports, switching positions and method of actuation the valves are classified.

3/2-way valve: ball seat Fig. shows a stem or plunger actuated 3/2 way valve. Unactuated position

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Actuated position

The 3/2-way valve has three ports and two positions. The addition of the exhaust port 3(R) enables the signal generated via the passage through the 3/2-way valve to be cancelled. The valve connects the output signal 2(A) to exhaust 3(R) and atmosphere in the initial position.

3/2-way valve hand slide valve: Fig. shows a 3/2 way valve hand slide valve.

The 3/2-way valve hand slide valve is used to supply air to a leg of the supply network upstream of the consuming devices. The construction of the valve is simple and it is used as a shut-off valve.

Servo controlled 3/2-way roller lever valve: Fig. shows a Servo controlled 3/2-way roller lever valve.

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To avoid a high actuating force, mechanically controlled directional valves can be equipped with an internal pilot valve and servo piston to assist opening. The valve actuating force is often the determining factor in applications and the servo assistance allows for larger bore valves to be operated with small actuating forces. This increases the sensitivity of the system.

5/2-way valve: longitudinal slide principle Fig. shows a 5/2-way valve.

The 5/2-way valve has five ports and two positions. The 5/2-way valve is used primarily as a final control element for the control of cylinders. The longitudinal slide valve uses a pilot spool as a control component. This connects or separates the corresponding lines by means of longitudinal movements. All forms of actuation can be used with longitudinal slide valves, i.e. manual, mechanical, electrical or pneumatic.

Solenoid controlled valves: In electro – pneumatics, valves are actuated by solenoids. Solenoid operating principle: If a conductor (a length of copper wire) is formed into the shape of one turn of a coil and a current is passed through the conductor, an electromotive force (EMF) is generated.

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The circular form concentrates the lines of force around the conductor. This circular form concentrates the EMF in one direction, whereas the straight conductor’s EMF is spread along its length. By adding turn to the conductor, the magnetic field is strengthened and the EMF is increased. For solenoid applications, an electromagnet consisting of simple coils of wire do not generate sufficient EMF to drive the stems of most valves. 3/2-way single solenoid valve normally closed: Fig. shows a single solenoid operated 3/2-way valve.

This NC valve is directly actuated by a solenoid and is returned to the idle position by spring return. 5/2-way single solenoid valve: Fig. shows a single solenoid operated 5/2-way valve.

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The 5/2 way valve performs a similar function as the 4/2 way valve. The main difference is that this valve has two exhaust ports, whereas the 4/2 way valve has one exhaust port. Energizing the solenoid moves the armature and opens the pilot air passage. The pilot air applies pressure to the right side of the valve piston, in turn forcing the suspended dics against the opposite sealing seat, resulting in: 

Air exhausts from 2 to 3



Exhaust port 5 is blocked



Air flows from 1 to 4

In the neutral state, the spring return forces the large diameter seal at the spring end against its seat, blocking airflow from 1 to 3. The spring force also loads the suspended disc against port 4 blocking the passage of air from 1 to 4. The suspended disc opens the air flow from 1 to 2. 5/2-way double solenoid valve: Fig. shows a double solenoid operated 5/2-way valve.

In case of a double solenoid valve, the spring return has been replaced by a second solenoid. Assuming that the last signal applied was at solenoid Y1, air flows from 1 to 2 and 4 is exhausted via 5. When the signal is removed from Y1 the suspended disc remains stationary and no change occurs in the switched state of the valve. 21

TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 A signal applied at solenoid Y2 reverses the valve and air flows from 1 to 4 and 2 is exhausted via 3.

Non – return valves Check valves: Check valves can stop the flow completely in one direction. In the opposite direction the flow is free with a minimal pressure drop due to the resistance of the valve. Blocking of the one direction can be effected by cones, balls, plates or diaphragms.

Two pressure valve: AND function The two pressure valve has two inlets and one outlet. Compressed air flows through the valve only if signals are applied to both inlets.

One input signal blocks the flow. If signals are applied to both X and Y, the signal which is last applied passes to the outlet. This valve is used mainly for interlocking controls, safety controls, check functions and logic operations.

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Shuttle valve: OR function This non-return valve element has two inlets and one outlet.

If compressed air is applied to the first inlet, the valve seat seals the opposing inlet. A signal is generated at the outlet. When the airflow is reversed, i.e. a cylinder or valve is exhausted, the seat remains in its previously assumed position because of the pressure conditions. This valve is also called an OR component.

Flow control valves These valves influence the volumetric flow of the compressed air in both directions.

One-way flow control valve These valves are used for speed regulation of actuators. In this valve, the airflow is throttled in one direction only. A check valve blocks the flow of air in the bypass leg and the air can flow only through the regulated cross-section.

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In the opposite direction, the air can flow freely through the opened check valve. These valves are mounted directly on the cylinder. There are two types of throttling circuits: o

Supply air throttling

o

Exhaust air throttling

Pneumatic timer (Time delay valve NC) These valves delay the signals. Fig. sho ws a NC type time delay valve.

The time delay valve is a combined 3/2-way valve, one way flow control valve and air reservoir. The delay time is generally 0 – 30 seconds.

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ELECTROPNEUMATIC COMPONENTS Relays Relays are electromagnetically operated devices very suitable for automatic control. They are relatively small and sensitive magnetic contacts capable of controlling large and remote loads, with high efficiency and matching accuracy.

Relays are used in switching circuits to amplify or multiply signals, to provide memory and to invert or convert signals. PE converter This device combines a pneumatically actuated stem and an electric switch. Fig. shows a PE converter.

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When a pneumatic signal of sufficient pressure to overcome the opposing spring force is applied to the diaphragm, the resultant force operates. The force required to operate the stem is controlled by the adjusting screw. Movement of the stem actuates a micro switch via a switching lever.

Contacts Switches are primarily distinguished by their contact configuration: 

Normally open (path 3 to 4)



Normally closed (path 1 to 2)



Change over contacts (path 1 to 2 or 1 to 4)

On actuation, a normally open (NO) contact enables energy flow and a normally closed contact (NC) disables energy flow. The changeover contacts (CO) can be used as either normally open or normally closed contacts.

Reed switches Reed switches are also known as m agnetically actuated proximity switches. Fig. shows the reed switch.

In Electropneumatic control circuits, reed switches are commonly used to sense the positions of pneumatic cylinder piston rods and the angle of rotation of shaft in rotary actuators. 26

TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Electronic sensors Certain applications require the use of electronic sensors employing: 

Electrical induction



Capacitance



Infra red light

These are represented by the following illustrated symbols.

PNEUMATIC CYLINDERS (ACTUATORS) Actuators Pneumatic cylinders convert pneumatic energy into mechanical energy. It has the following general characteristics: 

Diameters

2.5 to 320mm



Stroke lengths

1 to 2000mm



Available forces

2 to 45000 N at 6 bar



Piston speed

0.1 to 1.5 m/s

There are two types of actuators: 



Linear actuator o

Single – acting cylinders

o

Double acting cylinders

Rotary actuator o

Air motor

o

Rotary cylinders

o

Rotary actuator

Single – acting cylinders In single-acting cylinders compressed air can be applied on only one side of the piston face. Fig. shows a single-acting cylinder.

The cylinder can produce work in only one direction. The return movement of the piston is effected by a built-in spring or by the application of an external force. 27

TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 The single-acting cylinder has a single piston seal which is fitted on the air supply side. Sealing is by a flexible material that is embedded in a metal or plastic piston. During motion, the sealing edges slide over the cylinder bearing surface. There are varying designs of single-acting cylinders including: o

Diaphragm cylinder

o

Rolling diaphragm cylinder

Double - acting cylinders Fig. shows a double acting c ylinder.

There are two ports namely supply and exhaust ports. This cylinder has the capability to carry out work in both directions of motion.

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Fig. shows a double acting c ylinder with end position cushioning.

If large masses are moved by a cylinder, cushioning is used in the end positions to prevent sudden damaging impacts. The various types of double acting cylinders are: 

Tandem double acting cylinder



Cylinders with through piston rod



Multi position cylinders

Cylinders with through piston rod This cylinder has a piston rod on both sides, which is a through piston rod. There are two bearing points to guide the piston rod.

The force is identical in both directions.

Rotary cylinders With this design of double acting cylinder, the piston rod has a gear tooth profile. The piston rod drives a gear wheel, and a rotary movement results from a linear movement. 0

0

0

0

0

The range of rotation varies from 45 , 90 , 180 , 270 to 360 . The torque is dependent on pressure, piston surface and gear ratio. Rotary actuator With a rotary actuator, force is transmitted direct to the drive shaft via a vane.

0

0

Angular displacement is infinitely adjustable from 0 to approx. 180 . Torque should not exceed 10 Nm.

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Guidelines for Maintenance: 

The cylinder should be perfectly aligned for efficient and trouble free operation.



Piston rods dismantled during servicing, should be properly supported to retain it in line.



Tie rods connecting the end covers, should be tightened with equal tension as possible to avoid strain on the rods.



No reworking on cylinders should be taken on cylinders.



While servicing cylinders all seals are to be replaced.



Cylinders should be properly lubricated.

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 MAINTENANCE & TROUBLE-SHOOTING OF PNEUMATIC SYSTEMS

Maintenance need of Pneumatic systems While designing a pneumatic system, specific care should be taken to make the system simpler and easy to handle. Guidelines on pneumatic system 

It should be easy to operat e, reliable, light in weight, simple and e asily serviceable.



For each system, the circuit diagram and functional diagram should be available.



The control system should be as small as possible.



The impulsive valves should be guarded against dirt, cooling water and mechanical shocks.



Before assembly of the unit, care must be taken so that the unit is free of dirt. Do not open the ports of the elements before the line connection.



All elements must be given proper identification numbering from the circuit diagram.



The service unit should be visible, serviceable and be placed at a higher level than the rest of the equipment.



Valves should be assembled near to the drive units.



When dismantling and assembling valves and cylinders, take care of the sealing materials.



Silencers should be used as they decrease the noise of air.



Lines should be short, tension-free and bend-free.



Cut the plastic hoses straight.



Connections of plastic hoses to the elements must be screwed properly.

Maintenance schedule of pneumatic system A. Air mains, lines and fittings Name of work

Periodicity

1. Detection and arrest of leakage of air

Monthly

2. Thorough inspection of the complete line system

Once in a year

3. Inspection of unions, bends, tees, couplings, etc.

Once in 3 months

4. Pressure rating at strategic points

Once in 3 months

5. Condensate traps

Daily

6. Automatic draining of condensate

Once in 3 months

7. Airlines, shocks, cuts in lines and holes

Weekly

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B. FRL unit 1. Detection and arrest of leakage of air

Daily

2. Drain condensate from filter

Daily

3. Cleaning of filter cartridge

Half yearly

4. Pressure rating of pressure regulator

Monthly

5. Calibrate pressure gauge

Half yearly

6. Cleaning filter bowl and oiler bowl

Yearly

7. Top up oil level

Weekly

8. Clean up oil jet passage

Half yearly

9. Arrest oil leakage

Once in 3 months

10. Adjust oil jet

As needed

11. Change of oil after thorough cleaning of bowl

Yearly or Half yearly

C. Pneumatic control valves 1. Possible air leakage and its arrest

Monthly

2. Check for possible seal failure

Half yearly

3. Inspect actuating elements

Half yearly

4. Check valve adjustment

Half yearly

5. Check solenoid and its electrical parameter

Monthly

6. Mechanical damage to valves and their parts

Yearly or earlier

D. Air cylinders and Air motors 1. Check for leakage and its arrest

Monthly

2. Check the tie-rod tensions

Half yearly

3. Inspect the cylinder for force and speed accuracy

Weekly

4. Check alignment of piston, piston rod & cylinder body

Yearly or as needed

5. Mechanical damage to piston rod

Weekly

6. Replace cup seal

Half yearly or as needed

7. Check rpm of motor

Weekly

8. Check torque of motor

Weekly

9. Check vibration produced by motor

Weekly

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TROUBLE, POSSIBLE CAUSES AND REMEDIES

The following is a list of common pneumatic system operating problems and the corresponding possible causes and remedy for each trouble.

A. Compressor

Trouble

Possible causes

Dirt in suction filter

Remedies

Clean filtering plate and filter disc. Do not use gasoline for danger of explosion.

Defective sealing of cylinder

Mount fresh packing of the

head

cylinder head.

Valve interference through

Exchange valve insert plate.

dislocated valve seat and valve guide Worn out pistons and piston

Exchange piston with rings and

rings as well as worn out

also the cylinder if necessary

cylinder Inadeuquate performance

Piston rings broken or not

Repalce piston rings as per

sealed

manufacturer’s instructions.

End gap not staggered in

Stagger the end gaps, make

grooves

the rings free in the grooves.

Rough, scratched or

Replace

excessive end gaps

Cylinders or piston

Replace or repair

scratched, worn or scored

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Trouble

Possible causes

Remedies

Leaking cylinder valve

Adjust and stop leakage

Loose belt in compressor

Adjust the belt as

wheel, motor pulley

recommended

Motor with excessive end

Adjust the end paly

play in shaft

Carbon on top of the piston

De-carbonise

Leaking, broken or wornout

Adjust or replace

constant speed unloader parts Valve seats worn

Recondition valve seat

Worn or scored connecting

Recondition the conneting rod,

rod, piston pin or crank pin

replace or condition gudgeon

bearings.

pin and crank pin bearings.

Defective ball bearings on

Replace bearings

Unusual noise

crank shaft or on motor shaft

Loose motor fan

Tighten the motor fan

Cylinders or pistons

Rebore cylinders and replace

scratched, worn or scored.

pistons.

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Trouble

Possible causes Binding in machine leakage

Remedies Check linkage to ensure that excessive friction loads are not present.

Pressure too low.

Check the pressure at the cylinder to make certain that it is in accordance with circuit requirements.

Cylinder fails to move the load when valve is actuated

Cylinder undersized for

Re-calculate force needs and

loads

install appropriate sized cylinders to carry the load

Piston rod broken at piston

Disassemble and replace

end

piston rod.

Valve sticking or binding

a) Check for dirt or gummy deposits b) Check for worn parts

Cyinder sticking or binding

a) Check for overtightened packing on rod seal or piston. b) Check for misalignment or worn

Erratic cylinder action

parts. Loose tie rods

Tighten the tie rods according to manufacturer’s recommendations

Excessive pressure

Reduce the pressure to the rated limits.

Pinched or extruded seal

Replace the cylinder body seal

Seal deterioration

Check the compatibility of seal

Cylinder body seal leak

material with the lubricant used

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TVS TRAINING & SERVICES LTD Vanagaram, Chennai – 600 095 Rod gland seal leak

Torn or worn seal

Examine the piston rod for dents and nicks. Replace the piston rod if the surface is rough

Excessive or rapid piston seal

Seal installed incorrectly

wear

Check installation instruction and make necessary corrections

Valves

Trouble

Possible causes

Remedies

Inlet poppet not seating

a) poppet is damaged, it must

properly.

be replaced b) Dirt in poppet seals, clean it c) Poppet seat damaged, Replace the entire valve body assembly

Nicked, torn or swelling

Replace it

seals

Cylinder leaks

Leakage in the packing of the air cylinder connected to the valve. Replace the packings

Valve blows to exhaust

Damage spools

Replace it

Cylinder leaks Leakage in the packing of the air cylinder connected to the valve. Replace the packings Damage spools

Replace it.

Air supply pressure too low

Inspect the system for

and causes the valve to

undersized supply lines, sharp

actuate partially

bends, fittings and clogged

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filter elements or a defective pressure regulator and adjust. Water or oil contamination

Ensure that the air is dry and that the air filter is drained frequently

Low pilot or signal pressure

Check the valve specification for minimum pilot or signal pressure required

Poppet chatters

Swollen seals

Replace it

Varnish deposits in spool

Remove varnish using a water

valve

soluble detergent or solvent such as kerosene

Air supply pressure low

Inspect the system

Low pilot or signal pressure

Check the valve specification for minimum pilot or signal pressure requirements.

Poor or no lubrication

Check the system lubricator to see that it is working as it should

Faulty silencer/ muffler

a) Remove the silencer to see if valve performance has improved b) Clean the silencer to see if

Spool valve action is sluggish

valve performance has improved c) Verify if the silencer is of adequate size Water or oil contamination

Ensure the supply air is dry.

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Pneumatics

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