We had a fun time today trying to figure out the physics behind using needle valves to control flow to pneumatic cylinders, but never quite figured it out.
We think we understand how they work, basically restricting flow of the air toward/away from the cylinder to slow its activation without reducing the force (PSI). We have double solenoids and double acting cylinders and needle valves going to each side.
The question is are we supposed to reduce flow to the air input side, the venting side or both. Is here a way to slow extension without slowing retraction? We tried about every combination and were just confused in the end.
Put it on the venting side, not the feed side, that you want to slow down.
And don’t expect miracles, either.
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I’m not sure exactly how your flow restrictors work, but ours only restricted the flow in 1 direction (IE unlimited flow in the other). That allowed us to have different speeds for extension/retraction.
To slow the actuation of the cylinder we would restrict the exhaust of that actuation.
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We have a few different models. They all have what appears to be a threaded component which we assume opens and closes the needle valve. One has an arrow on it which made us wonder if it somehow restricted air in one direction only. his may be the source of our confusion.
Since the venting side in extension is the input side in retraction, if we want to slow both, do we restrict both?
Given it has an arrow, I would assume it works the same as ours. You can check which way it restricts the flow (probably in the direction of the arrow) by reading a doc, or connecting it to compressed air and seeing if the flow is restricted in a particular direction or both.
You would then have it (assuming it restricts in the direction of the arrow) restrict the air flowing away from the actuator (arrow pointing away from actuator).
You would then yes need one on each side (both pointing away so it affects the exhaust of the actuator).
Edit: If it restricts in both directions, it will restrict both actions if it is between the solenoid and actuator. If you only want it to restrict one direction, you can connect it to the exhaust port on the solenoid.
Apparently there are needle valves (which appear to be bidirectional) and flow restrictors (which only restrict one direction). I found this symbol on some of ours but am not sure what it means. Is the circle/arrow symbol the unidirectional flow?
So those it looks like will restrict flow in one direction and be unrestricted in the other.
You can see that the flow is restricted in both directions by the left symbol, however there appears to be a ball valve allowing unrestricted flow in that particular direction (direction away from circle arrow?).
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Put a needle valve between the solenoid valve and the extension side of the cylinder. Also put a quick exhaust valve between that needle valve and the cylinder. Don’t modify the retraction side (just tubing). I think this will do what you want.
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Quick exhausts work well, we used them when we used a cylinder to shoot in 2014 and a prototype shooter in 2018.
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