Miscellaneous pneumatic topics Typical limit valves

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.

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.

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+, B-, C+, C-, A- I II III

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. Start A+, B+, B-, C+, C-, A- I II III Normal supply

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.

Miscellaneous Pneumatic Topics End of Miscellaneous Pneumatic Topics