pneumatic note unit 4

7/31/2019 Pneumatic Note UNIT 4

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UNIT 4 : PNEUMATIC WORKING

SYSTEM (SENSOR)

is a device that measures a measurableattribute and converts it into a signal

which can be read by an observer or by

an instrument

For pneumatic this device can detect

moving parts to provide signals for theautomatic control of a work cycle

Position for sensor can be contact and


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- Sensor can be actuated by :-


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1. MECHANICAL SENSORS

FUNCTION : usually use as a limit switch

and build at the end stroke of the

cylinder

ROLLER LEVER VALVE

actuated when the roller lever istraversed by the cam of a cylinderin a certain direction. After release

of the roller lever, the valve isreturned to its initial position by a

return spring.


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DIRECTCONTROL OF SINGLE ACTING

CYLINDER1.

On operating the push button the airpasses through the valve from port 1 to 2

via the valve 1S into the piston chamber

of the cylinder 1A.

1. The pressure builds up and advances the

piston rod against the force of the

cylinder return spring.

1. On release of the push button, the valve

spring returns the 3/2 way valve to its

initial position and the cylinder retracts.

The control valveuse for single

acting cylinder isthe 3/2 way DCV. Ifthe cylinder is for

small capacity, theoperation can bedirectly controlledby a push button3/2 way DCV with

spring return.


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INDIRECTCONTROL OF SINGLE ACTING

CYLINDER

For a single actingcylinder with a

large pistondiameter.

Ex : to clamp a

work piece

1. In the initial position, the single-acting cylinder 1A

is retracted . A spring return 3/2 way pneumatic

valve is used to actuate the cylinder.

2. The valve 1S is actuated when the push button is

activated and pressure is applied to the control

port 12 of the control valve 1V. The control valve 1V

is actuated against spring force and is thusswitched to flow.

3. The pressure building up at the cylinder piston

causes the cylinder piston rod of the single acting

cylinder to extend.

4. The signal at the control port 12 remains as long as

push button is operated. Once the piston rod has

reached end position, it returns only after the push

button has been released.

5. When the push button is released, the valve 1Sreturns to its initial position. Control port 12 of the


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The logic AND function

1. The input 1 and 1(3) of the dual pressure

valve 1V1 are connected to the working

ports 2 of the valves 1S1 and 1S2. The

3/2-way roller lever valve 1S2 is actuated

by the insertion of a workpiece and then

creates a signal at one input of the dual-

pressure valve. Since only one input is

actuated, the AND condition has notbeen fulfilled and the output of the dual-

pressure valve remains closed.

1. If the push button of the 3/2-way valve

1S1 is now also actuated, a signal will also

be applied at the second input.

2. The AND condition is now fulfilled and a

signal is generated at the output 2 of thedual-pressure valve. The 5/2-way

The piston rod is toadvance when the

3/2way roller levervalve 1S2 is actuatedand the push buttonof the 3/2 way valve

1S1 is actuated. Ifeither of these isrelease, then the

cylinder return to theinitial position.


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4. If one of the two valves 1S1 or 1S2 is no

longer actuated, then the AND conditionwill no longer be fulfilled and the signal

at the output of the dual pressure valve

will be reset.

5. The signal pressure at the control port14

of the control element 1V2 is exhausted

to atmosphere via the reset valve 1S1 or

1S2. The control element 1V2 switches

back. The pressure building up on the

piston rod side ensures the retraction of

the piston rod.

The logic AND function (cont.)


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1. The inputs 1 and 1(3) of the shuttle valve1V1 are connected to the workingconnections of the valves 1S1 and 1S2.

2. Upon operation of one of the pushbuttons, the corresponding valve 1S1 or1S2 is actuated and a signal is generatedat the 1 or 1(3) side of the shuttle valve.The OR condition is fulfilled and the signal

passes through the shuttle valve and isemitted at port 2.

3. The signal pressure is prevented fromescaping via the exhaust of theunactuated valve by closing the line inthe shuttle valve. The signal effects the

switching of the control element 1V2.

4. The piston side of the cylinder ispressurised and the piston rod advances.

5. When the actuated push button isreleased, the signal pressure is relievedvia the valves 1S1 and 1S2 and the

The logic OR functionA double acting

cylinder is to

advance if one of twopush buttons is

operated. If the pushbutton is thereleased, the

cylinder is to retract


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Example of pneumatic circuit

1. One of the push buttons

need only be operated for a

short duration and thecylinder will fully extend,

since the effect of the

signal at input 14 of the

5/2-way double pilot valve

1V2 is maintained until asignal is applied at input 12.

2. As soon as the piston rod

has reached the forward

end position, the limit

switch 1S3 generates asignal at input 12, and the

valve1V2 is reversed.

3. The retracted end position

of the piston rod can alsobe sensed. This requires an

A double pilot valve should befitted for the control of the

cylinder. If the cylinder is toretract on reaching its fully

extended position, roller levervalve should be used as limit

valves to confirm that thisposition has been reached.


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Example of pneumatic circuit


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1. The addition of the dual pressure valve 1V2and the roller limit switch1S4 ensures that the

cylinder is fully retracted before the cylindercan be extended again.

1. The condition for a renewed advancing of the

piston rod is the actuation of one of the valves1S1 or 1S2 and the limit switch 1S4.

1. When the cylinder is advanced at position 1S3,the cylinder retracts even if the valves 1S1and 1S2 are still operated since the limitswitch 1S4 is inactive


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Electro-Pneumatic circuita) Solenoid

1. function ; primary used to control theswitching of valves, relays or contactors.

2. If current flow through the solenoid coil,the piston of the valve is actuated

3. If the current is interrupted, a springpushes the piston back into its initialposition

b) Relay1. Is an electromagnetically actuated switch

2. Application : signal multiplication, delaying

and conversion of signal.

pneumatic note unit 4

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