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• Different types of actuation
Pneumatics Part 2 Compressed air systems, components and circuits By Amaren P. Das
[email protected]
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Manual Mechanical Pneumatic Electrical Combined
Mechanical
• Manual
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• Poppet valve: long service life but large actuation
Pneumatic
force is required
– Ball valve – Disk seat valve Disk seat valve
• Slide valve Electrical
– Longitudinal slide valve (spool valve) – Longitudinal flat slide valve – Plate slide valve
Combined
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• Has two ports and two position • Rarely used except as an on‐off valve • Normally of ball seat construction
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• Hand operated
• Construction and working principal of 3/2 valve – Explain the working principle of valve – Find what the circuit does
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• Pilot actuation – 12 pilot line – Spring to reset – Can be configured as normally open or normally closed
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3/2 normally closed ball seat
3/2 normally closed disk seat
Controlling a single acting cylinder
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• Has 4 port and 2 position • Similar in construction to two 3/2 valve • One valve normally closed other normally open
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• Types of 5/3 valve
• 4 ports and 3 position • Center position blocked • Can be used to hold cylinder at the middle of the stroke • Position of the cylinder is not accurate as extra load will change the position
– Blocked center • The cylinder is fixed at its position when the valve is un‐actuated
– Open center • Generally used when the piston of the cylinder is to be moved by hand or some other tool during operation cycle
– Pressure center • Same as the blocked center but any leak through the seals are compensated and pressure is always maintained NFC TS 2009 Pneumatics APDas
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• Construction and working principal of 5/3 valve
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• Stops flow in one direction and permits flow in the reverse direction • Blocking in one direction can be effected by cone, balls, plates or diaphragm
– Has 5 working ports – 3 switching positions – If no signal is applied at If no signal is applied at either of the two ports, the valve remains spring‐ centered in the middle position – Notice the two springs on both side in the symbol it is essential
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• Has to inlets 1 and 1(3) and one outlet 2 • When signal is present on both inlet port then only signal is available on output port 2. The signal which is last applied is • The signal which is last applied is passed through the port. • One input signal on 1 or 1(3) block the flow due to differential pressure • If inputs are at different pressure, the lower of the two passes through the valve • It function as an AND gate
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• It has two inlets 1 and 1(3) • If any of the inlets is pressurized the signal is available at the outlet port • The valve performs the logic OR function OR function • When air flow is reversed , the seat remains in its previously assumed position because of the pressure condition • If cylinder is to be operated from one or more positions, one or more shuttle valve must be used 13
• Actuating cylinder from two different positions. • What changes are required if we want required if we want to actuate it from three positions ?
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• Used to increase the piston speed • It opens a large exhaust area near the cylinder port. • Lengthy return time is avoided in single acting cylinder
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Flow from 1 to 2
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Flow from 2 to 3
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• Shut off valves are non‐ adjustable valve, which releases or shut off flow in both directions
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• Flow is controlled only while flowing from 1 to 2 • Flow from 2 to 1 is free of any obstruction • Is used in speed regulation of cylinder
• Controls volumetric flow of compressed air in both directions. • It throttles the air by y increasing or decreasing the flow area • It is normally adjustable • It is used to control the speed of cylinder
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• For a double acting cylinder should inlet air be throttled or the exit air ? And why ? • In case of inlet throttling there will be huge fluctuation of speed in the cylinder motion if the load on the cylinder slightly changes, i.e. while crossing roller limit switch. li h l h i hil i ll li i i h • Load variation on the cylinder hardly effects the speed of cylinder, as the piston is traveling between two air compressed air. Exhaust throttling
Inlet throttling
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• Maintains constant pressure at the outlet even with fluctuating inlet pressure • The inlet pressure must be greater than required pressure
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• If the pressure in line 12 is greater then the spring force, the out port 2 is connected to port 1.
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• It is a combination of 3/2 valve , one flow control valve and a reservoir . • 3/2 valve can be normally open or closed valve • The time delay is between 0 to 30 sec • 3/2 valve actuates only after the reservoir is completely filled to a pressure which counters the spring force. • The rate of flow to the reservoir is determined by the flow control valve, which sets the time interval. • Figure in next page
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• For trouble free and continuous performance of control system, air supply should be – Maintained at required pressure – Dry – Clean
• Equipment used in generation and prepration of air d d f – – – – – – – – NFC TS 2009 Pneumatics APDas
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Inlet filter Compressor Reservoir / receiver Air dryer Air filter with water separate Pressure regulator Lubricator if required Drainage points NFC TS 2009 Pneumatics APDas
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• Reciprocating
• Pressure Level – Components are designed for maximum pressure up to 8‐10 bar – Practical experience has shown that approx 6 bar Practical experience has shown that approx 6 bar should be used for economic operation – Pressure loss up to .1 bar must be expected due to restrictions bends, leaks and pipe‐run – The compressor should generate pressure between 6.5 to 7 bar NFC TS 2009 Pneumatics APDas
• • • •
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• Rotating Piston g – Sliding vane – Twin shaft screw – Roots compressor
• Flow compressor (used high flow rate but low pressure) – Radial flow compressor – Axial flow compressor
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• It the first component down stream of a compressor • Why it is needed?
Most common Wide range of pressure and delivery rate For high pressure use multistage Optimum range of pressure for reciprocating compressor
– Stabilizes compressed air, removes pressure fluctuation – Stores the air, so that compressor does not have to run continuously – Stored air can be used as an when required by the system – Provides the compressed air to cool down, portion of the moisture is removed the air
– Up to 4 bar Single stage – Up to 15 bar Double stage – Over 15 bar Treble Stage NFC TS 2009 Pneumatics APDas
– Piston – Diaphragm ( no contamination, used in food and pharma industry)
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Use nomogram to determine the size of Reservoir
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– Delivery volume, QL = 20 m3/min – Switching cycle per hour, Z=20 l/h – Differential pressure (higher set point – lower set point), ΔP= 0.1 bar – Result: Receiver size ,VB=15m3
The service unit consisting of Filter‐ separate , Regulator and Lubricator, also called FRL unit Filter‐ separate is used to filter out condensed water, contamination and excess oil.
– Pore size determines the smallest particle that can be filtered out can be filtered out – The usual pore size is between 5 micron to 40 micron – Condensate collected should be manually drained out. – Over use of filter may lead to heavy energy loss, due to pressure drop across it
Filter
Filter and separate manual NFC TS 2009 Pneumatics APDas
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Construction of FRL unit • •
Regulator is nothing but a pressure regulator Lubricator
– For some components lubrication is damaging ‐>damages seals – Control units do not need lubricated air – Power components may need lubrication Power components may need lubrication – Lubrication by means of mist lubrication is required when • Extremely rapid oscillating motion is required • Cylinders of large diameter – Mist Lubrication is done based on venturi action
• Filter construction
• Lubricator construction
Pressure regulator Pressure regulator with indiacator
Lubricator
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Air distribution • Distributed using Pipes • Pipe diameter should be selected using Nomogram • Pipe line must be installed in direction of flow with a gradient of 1 to 2 degree • Any branching of air consumption point where lines run horizontaly should always be installed on the upper side of main line • Condensate removal are installed on the under side of main line NFC TS 2009 Pneumatics APDas
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• Plastic Pipes are mostly used as no brazing, welding or joining with threaded components are required yp pp g y • Types of main piping lay out – Branch Line – Ring Line – should normally be used – Interconnected circuit
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Ring Main
Interconnected Main
• Ring main ensures largely constant pressure conditions NFC TS 2009 Pneumatics APDas
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Th k Thank you
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