# Pneumatic cycle A+A-A+A-



## chimaerion (Oct 27, 2016)

Hi,

I was wondering how one would accomplish the following cycle purely pneumatically (no electronics/sensors whatsoever):
A+A-A+A-. 
So suppose you have double working cylinder and the shaft first goes out then back in, then again out and lastly back in. So no continuous cylce.
I think one would need a mechanical/pneumatic counter to count the strokes.
But how can one achieve such thing? I have googled alot and read my school books, but I didn't find anything.

Can you guys help me out?


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## corey872 (Jan 10, 2010)

I guess you'd need to set up one 3-way valve and one standard valve. The 3-way valve would need to be connected to the cylinder by a linkage so when the cylinder extended to the desired position, the valve would be moved to supply air to the 'retract' side of the cylinder, then when the cylinder retracted to the desired position, the valve would be moved to supply air to the 'extend' side of the cylinder. This would create an un-ending reciprocating motion.

To get it to only go twice, your on-off valve would be up-stream of all this and plumbed to turn air on or off to the whole works. it would need to be moved off by a mechanism that takes two strokes to complete... perhaps a ratchet driving a cam gear? or a standard crankshaft assembly with 2:1 gear reduction and the final gear has a pin which moves the standard valve to off. 

The two main concerns would be to have the on-off valve triggered in such a manner that once off, it is free to move on again. ie you don't want it rigidly attached to the cam or gear, then you are stuck in a chicken/egg situation where the machine needs to move to turn the vave on, but also needs to turn the valve on to move.

Secondly, you'd need to account for a bit of 'carry through' on the second stroke. You want the cylinder to be 'primed' and ready for the extension with the 3-way valve just slightly cracked to the extend position. If it stops at 'retract dead center', then even switching the air back on would have it still locked up and needing a nudge. Perhaps a small spring at the bottom would let it retract all the way, turn off, but then nudge everything forward just a bit - ready for the extend when the air is turned back on.


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## chimaerion (Oct 27, 2016)

Thanks for answering. But the reason I asked this question was because I am student (elektromechanics) and this is a practical exercise we have to do in school in the lab.
While your idea might work, it is a little hard to execute such an idea at school, because we have like only a few hours and can only use generic pneumatic pieces like cylinders and valves to achieve this.


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## BillyVanpire (Apr 22, 2015)

here's an A+A B+B example, that help?


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