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Pneumatic training report

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					22 January 2005

TRAINING REPORT
COMPANY: - FESTO CONTROLS PVT LTD.

PLACE: - MUMBAI

PERSON: Amit M. Rampure

FACULTY: - V. A. Kowshik

PURPOSE: - Festo Didactic Training Program on Basics of Pneumatics.

AIM: To familiarize with fundamentals of pneumatics and develop skills required to design, maintain and troubleshoot systems that works purely on air.

CONTENT:            Elements in pneumatic systems Air preparation and distribution Cylinders and valves Special purpose valves Port numbering systems Design and construction of pneumatic circuits Pneumatic latches and their applications Maintenance and troubleshooting Safety considerations Air consumption calculations Cylinder force calculations.

DATE: - 17~21 January 2005

TIMING: - 9.00am to 5.00 pm

 INTRODUCTION In morning Peoples from BFL and Festo introduced each other. After introduction the purpose of training and courseware of training (Text book of Basic Pneumatics) is given.  Pneumatics is system of fluid power in which Compressed air is used for doing certain work. Pneumatic components can perform following types of motion:  Linear  Swivel  Rotary.  Basic difference in Hydraulic and Pneumatic Consider the characteristics of hydraulic and pneumatic system. The graph of pressure v/s Volume of air pumped into cylinder for both the systems is as shown. 1. Without load

P

V HYDRAULICS PNEUMATICS Explanation: In Hydraulic systems, the pressure rises suddenly after the certain volume of air is filled into cylinder; which develops a large force. In Pneumatic systems the pressure rises slowly as compared to the hydraulic system; therefore the it does not develop large force.

2. With load

P

V

Explanation: In Hydraulic systems, the pressure rises to a value at which load can be momentarily moved after that the pressure suddenly rises which gives large force In Pneumatic systems the pressure rises slowly as air is filled into the cylinder but due to load the small layer near to the piston is get compressed due to which pressure doesn’t rise even if volume is increasing. When the air pressure is sufficient to move the load is built the load moves which creates a space therefore the air is expanded and pressure doesn’t built as much after pumping more air into cylinder the pressure rises slowly and load moves. This gives rise to jerky motion at rod end.

Sr no. 1. 2. 3. 4. 5. Media used Force developed Speed Safety Transport of media Oil

HYDRAULICS

PNEUMATICS Compressed Air Force is lower than hydraulics Very high Very safe.

Very high force Slow Less than pneumatics

Oil cannot be transferred Air can be easily transported in over large distances pipelines over large distances. Compressed air offers no risk of explosion or fire

6.

Explosion proof

Oil can cause explosion

7.

Environmental effects

Leakage oils can cause air Air cannot cause any air pollution lubrication

8.

Temperature effects The oil is sensitive to temp. Compressed air is relatively effects, insensitive fluctuations. to temperature

9.

Cost

Relatively high cost

Relatively low cost

 Disadvantages of Pneumatic system  PREPARATION Compressed air requires good preparation; dirt and condensate should not be present. COMPRESSION It is not always possible to achieve uniform constant piston speeds with compressed air FORCE REQUIREMENT Compressed air is economical only up to certain force requirement under normal working pressure of 6 to 7 bar and dependent on travel and speed , the output limits between 40000 and 50000 N. NOISE LEVEL The exhaust level is loud. This problem is now solved due to sound absorption materials silencers.

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

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 SELECTION CRITERIA 1. Working media Electricity  Fluids (hydraulics)  Compressed air (pneumatics)  Combination of above 2. Working section requirements  Force  Stroke  Type of motion  Speed  Service life  Safety and reliability  Energy costs 3. Control section  Mechanical  Electrical/electronics  Fluids  Compressed air



Development of pneumatic system The following points considered while developing any pneumatic circuits:  Reliability  Ease of maintenance  Cost of spare parts  Assembly and connections  Maintenance and repair costs  Interchangeability and adaptability  Compact design  Economic



PERFECT GAS LAWS

Because pneumatics involves gases, the laws that govern gases are very important. The "Perfect Gas Laws" express the relationships between pressure, volume, and temperature. When applying these laws, remember that only absolute values of pressure and temperature can be used. 1) Boyle's Law - This law expresses the relationship between pressure and volume when temperature is held constant. According to Boyle's Law, the volume of gas in a container is inversely proportional to the absolute pressure on the gas. Or, P1V1 = P2V2 2) Charles' Law - This law expresses the relationship between volume and temperature when pressure is held constant. According to Charles' Law, the volume of gas in an expendable container is directly proportional to the absolute temperature. Or, V1T2 = V2T1 3) Gay-Lussac's Law - This law states that if the volume of a gas is held constant (i.e., confined in a rigid container), the absolute pressure of the gas is directly proportional to its absolute temperature. Or, P1T2 = P2T1  AIR LEAKAGES AND ITS EFFECTS  SOURCES 1. 2. 3. 4. 5.  Pipe joints and flanges Connections fittings Cracked tubes Loose components Defective gaskets and O-rings

EFFECTS 1. Increased power consumption. 2. Drop of pressure

3. 4. 

Pressure fluctuations Additional cost for repairing

AIR PREPARATION AND DISTRIBUTION. The compressed air supply to a pneumatic system is adequately calculated and of required quality as per application. The air is compressed by the compressor and supplied to distribution system. The various malfunctions can be reduced by preparing good quality air. A number of aspects are considered for preparation of air. 1. Quantity of air required. 2. Type of compressor used 3. Pressure requirements 4. Air cleanliness 5. Lubrication requirements 6. Drainage points and exhaust in the distribution system 7. Correct layout of the distribution system A reservoir should be used to reduce the pressure fluctuations. The pipe diameter is selected such that it should compensate for the pressure loss from reservoir to application. RING circuit is most frequently used as main lines. This method achieves a constant supply in case of high air consumption. The pipelines must be installed in direction of flow with gradient of 1 to 2º. The condensate is removed from line at the lowest point. Any branching of air consumption should always installed on upper side of main line. Branching for condensate is to be installed on lower side of main line.  Air Service Unit This consist of 1. Air filter (with water separator) 2. Air pressure regulator. 3. Air Lubricator.

The air filter has to remove the contaminants dust dirt from the compressed air as well as water, which has condensed. The air filter should be appropriately selected as the too fine mesh filter clog easily and frequently as compared to standard filter. The purpose of regulator is to keep operating pressure of the circuit virtually constant regardless of fluctuations in the line pressure and air consumption. The lubricator is used to deliver the meted quantity of oil mist into leg of air distribution system.



Air Dryers. When pneumatic components wear or become corroded as a result of moisture, they consume more compressed air - and lose energy efficiency. When this wear or corrosion becomes great enough, components must be repaired or replaced - increasing operating expense. Dryers remove water vapor from the air, which lowers its dew point - the temperature to which air can be cooled before water vapor begins to condense. There are basic three types of dryers: 1. Refrigeration dryers. Refrigeration dryers condense moisture from compressed air by cooling the air in heat exchangers chilled by refrigerants. These dryers produce dew points in a range from 35° to 50° F at system operating pressure. 2. Adsorption dryers Deliquescent dryers contain a chemical desiccant, which absorbs moisture contained in the air, whether the moisture has already condensed or is still a vapor. The desiccant is consumed in the water-removal process and must be replenished periodically. 3. Adsorption dryers. Regenerative desiccant dryers remove water from air by adsorbing it on the surface of a microscopically porous desiccant, usually silica gel, activated alumina, or molecular sieve. The desiccant does not react chemically with the water, so it need not be replenished. However, it must be dried, or regenerated, periodically.



ELEMENTS IN PNEUMATIC SYSTEMS

COMMAND EXECUTION

POWER COMPONENT Pneumatic cylinders, Motors CONTROL ELEMENTS D. C. valves

SIGNAL OUTPUT

SIGNAL PROCESSING

PROCESSING ELEMENTS D. C. valves Non-Return valves Pressure control valves Timers, Sequencers

SIGNAL OUTPUT

INPUT ELEMENTS Push button valves Roller lever valves Proximity switches

ENERGY SUPPLY

SUPPLY ELEMENTS Compressor Reservoir FRL unit

NOTE: Direction control valves can be used as input processing, output elements.



VALVES The function of valves is to control the pressure and/or flow rate on media. Depending on design they are divided in following categories: 1. 2. 3. 4. 5.  Direction Control valves. Non-Return valves Flow control valves Pressure control valves Shut-off valves.

Direction Control valves These valves are described by  Numbers of ports openings. eg 2 way, 3 way.  Numbers of positions eg 2 positions 3 positions.  Method of actuations. eg manually actuated, electrically actuated.  Method of return actuation. eg spring return, air return.  2/2 valve The 2/2 valves have 2 ports 2 positions. This is on off valve. Its function is to enable signal only in one direction. 3/2 way valve The 3/2-way valve has three ports and two positions. In the normal position the valve closes P against A, exhausts A to R. The pressure applied to the plunger closes the pressure exhaust line before the valve disc lifts from its seat thereby opening P to A.    4/2 way valve The 4/2-way valve has four ports and two positions 4/3 way valve The 4/3-way valve has four ports and three positions 5/2 way valve The 5/2-way valve has five ports and two positions 5/2-way directional control valves are used to control double-acting cylinders. Spool valves have low actuating forces and permit flow in both directions. Unoperated: P connected with B A exhausted to R S closed Operated: P connected with A B exhausted to S R closed 5/3 way valve

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The 5/3-way valve has five ports and three positions

3/2-Way Directional Control Valve

5/2-Way Directional Control Valve

Flow Control valve  Speed of cylinder depends on rate of flow of air entering or leaving the system.  Slowing down the rate of flow of air entering or leaving; slows down the cylinder.  Air that is entering into cylinder is known as Inlet air.  Air that is leaving the cylinder is known as Exhaust air.



There are two methods of flow control as follows: 1. Inlet Flow control The inlet flow control method controls the inlet flow to cylinder (flow passes through restriction only) while exhaust flow passes freely. This method is not very efficient as it gives slow jerky motion during load; hence not preferred. 2. Exhaust flow control. In this method the inlet flow passes into cylinder without any restriction while the exhaust flow passes through restriction. This method is efficient as it gives slow and continuous motion.

4 14

2 23

12

5 1

3



Actuators and Output devices

An actuator is an output device for conversion of energy supply to useful work. The output signal is controlled by control element. The pneumatic actuators can be classified as:  Linear 1. Single acting cylinder 2. Double acting cylinder  Rotary 1. Air motor 2. Rotary cylinders 3. Rotary actuators. 1. Single acting Cylinder. The compressed air can be applied on only one side. This cylinder produces motion in only one direction only. This cylinder has spring return. 2. Double acting cylinder. This cylinder is used when there is substantial load in both the directions.

3. Rotary Cylinders. 4. Rotary actuator

5. Rodless cylinder



Cylinder Mountings. The type of mounting is to be decided by as per application and how the cylinder is fitted on the machine.




DESIGN OF PNEUMATIC CIRCUITS General procedure for designing of circuits.         Understand the application correctly. List down all the inputs. (May be operator inputs or machine inputs) List down all outputs and required conditions. Understand the safety interlocks, Sequential interlocks, and process interlocks. The structure of the circuit diagram should corresponds to the control chain whereby signal flows from top to bottom. The simplified or detailed symbols may be used for representation of circuit. The circuit is built by taking into considerations 1,2,3,4 points. Upon completion of the circuits, final circuit is evaluated and all inputs and outputs are verified. 1. AND circuit

2. OR circuit

3. NOT CIRCUIT

4. NAND CIRCUIT

5. NOR CIRCUIT



Pneumatic latches. 1. This is on/off circuit. If start push button is pressed the circuit will operate and stop is pushed it will stop the working.

START

STOP

2. Dominant Set circuit-if both start and stop push buttons pressed at a time then it is called as Dominant set. This circuit resets its original position when power becomes on and off.

START

STOP

3. Dominant Rest circuit

STOP

START



Creating 3/2 valve from 5/2 valve

Blocked 4 2 4

Blocked 2

5 1

3

5 1 3

Normally closed 3/2 way valve

Normally open 3/2-way valve

HIERARCHY OF ELEMENTS

Flow Control Valve Quick exhaust Valve

Flow Control Valve Quick exhaust Valve

Direction Control Valve (Power valve) Direction Control Valve Pressure Sequence Valve Pneumatic Timers Dual Pressure (AND) Valve Shuttle (OR) Valve Limit Switches Push Buttons Pneumatic Sensors
Low Pressure Low Flow rate Zone < 4 bar

Service unit Pressure regulator

Direction Control Valve Pressure Sequence Valve Pneumatic Timers Dual Pressure (AND) Valve Shuttle (OR) Valve Limit Switches Push Buttons Pneumatic Sensors
Low Pressure Low Flow rate Zone < 4 bar

Main Air Supply
High Pressure High Floe rate Zone > 4 bar

Common Symbology in Pneumatics

2/2 Valve; 2 Ports, 2 Positions

3/2 Valve; 3 Ports, 2 Positions

4/2 Valve; 4 Ports, 2 Positions

4/3 Valve; 4 Ports, 3 Positions

5/2 Valve; 5 Ports, 2 Positions

5/3 Valve; 5 Ports, 3 Positions

Accumulator

Air Dryer

Air Motor (One Directional Flow)

Air Motor (Two Directional Flows)

Check Valve (Spring Loaded)

Compressor

Cylinder (Spring Return)

Cylinder Double Acting (Double Rod)

Cylinder Double Acting (Single Fixed Cushion)

Cylinder Double Acting (Two Adjustable Cushions)

Differential Pressure

Direction of Flow

Exhaust Line or Control Line

Filters and Regulators

Filter (Automatic Drain)

Filter (Manual Drain)

Fixed Restriction

Flexible Line

Flow Control Valve

Flow Gauge

Lever

Lines Connected

Lines Crossing

Lubricator

Muscular Control

One Bypass Flow Path and Two Closed Ports

One Flow Path

Pedal or Treadle

Pilot Pressure (External)

Pilot Pressure (Internal)

Plugged Port

Plunger or Position Indicator Pin

Pneumatic

Pressure Actuated Electric Switch

Pressure Gauge

Pressure Regulator (Adjustable, NonRelieving)

Pressure Regulator (Adjustable, SelfRelieving)

Pushbutton

Quick Acting Coupling

Roller

Roller (One-Way)

Shuttle Valve

Silencer

Single Square

Solenoid and Pilot; Manual Override and Pilot

Solenoid Spring Two Closed Ports



PORT NUMBERING AND LETERING SYSTEMS.

NUMBER 1 2, 4 3, 5

LETTER P B, A S, R

SIGNIFICANCE Pressure source Working /Output ports Exhaust port

2 23 12
1 3 3/2 Valve; 3 Ports, 2 Positions Z

A Y
P S

4

2 12 Z

A

B

14 5 1 3

Y

RP S
5/2 Valve; 5 Ports, 2 Positions

NOTES:  The port at which supply is given is termed as 1 or P.  Generally Odd numbers are at bottom and Even numbers are at top of the valve symbol.  The actuations are numbered in the fashion as numbers from supply port and the port to which it is connected is combined in respected actuated positions. Eg in 3/2 way valve if push button is pressed then actuated number is 12  In lettering system the left side actuator is termed as ‘Z’ and right side actuator is termed as ‘Y’.

 MAINTENANCE OF PNEUMATIC SYSTEMS A systemic procedure for finding and eliminating faults reduces the downtime of pneumatic systems. Faults generally occur by  External failures of machine components  Internal failures within control system.  Causes of Failures 1. 2. 3. 4. 5. 6. 7. 8.  Wear and tear Ambient Conditions (Temperature, Humidity etc.) Quality of Compressed air used. Relative motion of components. Incorrect and insufficient Maintenance. Absence of Lubrication. Incorrect mountings, loading, connections. Certain components are never supplied with Lubricated air.

Effects of failures 1. Blocking of lines 2. Seizure of units 3. Breakages 4. Leakages 5. Pressure drop 6. Incorrect switching.

 Short Term Preventive Maintenance 1. Adjust and Refill the Lubricators. 2. Drain water from Piping and water Separator. 3. Clean Filter element with Compressed air. 4. Regular maintenance of FRL unit.  Long Term Preventive Maintenance 1. Check Seals of connectors for leak. 2. Replace tubes connected to moving parts. 3. Check and replace Filter elements. 4. Check and replace Rod end Bearing. 5. Check function of Safety valves. 6. Develop and Continuously update Long Term Strategy for Maintenance.  Symptoms of Incorrect Maintenance 1. Frequent Rod Breakage. 2. Gumming of moving parts. 3. Frequent leaks and Blockages. 4. Seizures. 5. Long switching time. 6. Non-uniform movement of piston. 7. Loss of force in the cylinder. Breakdown Maintenance 1. Perform Root Cause analysis.



2. Take Preventive steps to ensure that problem does not occur again. 3. Isolate area of Problem and offending components. 4. Replace and repair Defective/Weak components.  Air Usage 1. Leakages in Joins and hose Connection. 2. Air distribution does not follow specific strategy. 3. Bending of pipes are not done properly. 4. Absence of reservoir, dial gauges at critical locations. General Maintenance faults. 1. Pressure valves are mounted in open without protection enclosure. 2. No silencers on valve exhaust ports, 3. Lubricators misadjusted or defective.  Troubleshooting of pneumatic systems. 1. Understand the circuit function and component symbols. 2. Understand port-numbering system of valves. 3. Troubleshoot from Bottom to top of the circuit. 4. Analysis of circuit problems. Typical problems in pneumatic system. 1. Seal wear.  Due to internal friction. When small pressure air (1~1.2 bar) is supplied at the rear end of cylinder the cylinder moves in slow or irregular fashion.





Slow /irregular motion

1~1.2 bar



Internal leakage. To detect internal leakage, the compressed air is supplied (about4 bar) from the rod side and dial gauge is connected on the rear side of the piston.; in case of leakage, the dial gauge shows a high reading.



Rod end seals The leakage of air can easily detected.

2.

Valve seal wear. Block the output port 2, 4 and provide supply of pressure of 4 bar to input port. The dial gauge is connected to other input port 5. If there is leakage of air; dial gauge shows the fluctuations of pressure.

4

2

5

1 4 bar



Cylinder force calculations.

The piston force exerted by cylinder is dependent on the air pressure P, cylinder diameter D and frictional resistance FR. See graph of piston diameter v/s force on page no 171; we can find for certain pressure and diameter what is the force. *{For single acting cylinder, Theoretical piston force Fth= A x P Actual piston force Feff = (A x P)-(FR + Fspring) For double acting cylinder, Feff = (A x P)-FR Feff = (A’ x P)-FR }  ----Forward stroke ---Return stroke

Air Consumption Air consumption is directly proportional to the Pressure and stroke Volume. See graph of piston diameter v/s Air Consumption on page no 174; we can find for certain pressure and diameter what is the air Consumption.

*{Air Consumption = Compression ratio x Piston surface x stroke x strokes no. per minute Compression ratio = 101.3 + operating pressure (in Kpa) 101.3 }


				
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