Miscellaneous pneumatic topics Typical limit valves IA Misc

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Miscellaneous pneumatic topics Typical limit valves IA – Misc. Pneumatic Topics 1

Miscellaneous pneumatic topics Typical limit valves IA – Misc. Pneumatic Topics 1

Control of Speed • Piston retracts rapidly. • Forward motion’s speed controlled by restrictor.

Control of Speed • Piston retracts rapidly. • Forward motion’s speed controlled by restrictor. • For smooth motions, speed is controlled by restricting air venting to atmosphere. Speed of motion in both directions controlled by respective restrictors. IA – Misc. Pneumatic Topics 2

Emergency-Stop modes: Stop-Restart Devices • For Start-Stop purposes, we need to generate a controlled

Emergency-Stop modes: Stop-Restart Devices • For Start-Stop purposes, we need to generate a controlled air supply C. • Pressing a STOP pushbutton will de-activate C, i. e. vent it to atmosphere. Pushing RESTART will activate it again, i. e. power up C. IA – Misc. Pneumatic Topics 3

Emergency-Stop modes: "No-Change" Stop Mode When STOP is pressed: • any cylinder at rest

Emergency-Stop modes: "No-Change" Stop Mode When STOP is pressed: • any cylinder at rest remains at rest and any cylinder in motion completes its stroke and then come to rest. • This mode of operation is easily achieved by using the C signal as the line supply air to the various limit valves. • When the C signal is reactivated by the RESTART button, the sequence resumes from where it is interrupted. Normal Air Supply Start A+, B-, C+, C-, AI II IA – Misc. Pneumatic Topics 4

Emergency-Stop modes: "No Motion" Stop Mode When STOP is pressed: • Pressure from both

Emergency-Stop modes: "No Motion" Stop Mode When STOP is pressed: • Pressure from both sides of moving pistons are vented to atmosphere. All pistons will then come to an immediate halt. • To achieve this mode of operation, the C signal is connected to the line supplying air to the various cylinder control valves. • When C is reactivated, the sequence resumes from where it left off. Normal supply Start A+, B-, C+, C-, AI II IA – Misc. Pneumatic Topics 5

Generation of Time Delays • Generated using restrictors (Needle valves, N), Check Valves, C,

Generation of Time Delays • Generated using restrictors (Needle valves, N), Check Valves, C, and an air Volume, A. Length of delays varied by varying A and N. • When signal comes to move +ve, air cannot flow left through C, and is forced to flow slowly through N. Pressure slowly builds up in A until it moves control valve, thereby causing cylinder to extend. • There is no time delay for retraction of cylinder because air on the + side of the control valve can vent to atmosphere quickly through C. IA – Misc. Pneumatic Topics 6

End of Miscellaneous Pneumatic Topics IA – Misc. Pneumatic Topics 7

End of Miscellaneous Pneumatic Topics IA – Misc. Pneumatic Topics 7

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