Double Action/Spring Return Pneumatic Actuators

[twiegner]

My team is looking to use a Spring Return piston to possibly eliminate the need of an onboard compressor (we only need 1, 6" stroke actuator). We are looking to know 2 things
1: Will spring return pistons only use the equivalent of 1 burst or is there a drawback to these actuators?
2: Where would we get one of these actuators, our normal supplier is Bimba but I can't seem to find larger spring return actuators. I found mini actuators but they only have a max of around a 2" stroke and we need 6".

[Joe G.]

The primary drawback of spring return cylinders is reduced force for a given bore size, since the pressure must overcome the spring while extending, and must use this same, relatively weak spring for the return stroke. Depending on your application, this may be a non-issue.

[twiegner]

Ah yes, were just pushing a frisbee so that shouldn't be to much of a problem.

[Kevin Thorp]

What you're talking about is a single acting cylinder. Unfortunately this type is typically only available in short strokes. The internal spring needs to be approx. 2X the stroke length, so it isn't practical for longer cylinders.

You could simulate a single acting cylinder by leaving the air fitting off the nose end of a double-acting cylinder and using an external spring or elastic to retract your piston. Be careful not to side-load the piston rod, especially when fully extended. That's when it's most vulnerable to damage.

[twiegner]

Hmmm... at the workshop we went to at kickoff, the team had a nice long spring return actuator that went at least 6" if not 8", they mentioned where they got their pneumatics but I cannot remember at the moment. As for an external spring, at that point it may be more trouble than its worth, if anyone does know of a place to buy a 6" stroke spring return pneumatic actuator that would be fantastic, otherwise we may use a rack & pinion setup with a limit switch to do auto return and not use pneumatics or just do some precise calculations to see how much air we would need stored to shoot and return a piston as many times as we think is reasonable.

[AlexH]

or you could have another reg in the system to run at a lower pressure for the return stroke.

[George C]

Originally Posted by Kevin342

What you're talking about is a single acting cylinder. Unfortunately this type is typically only available in short strokes. The internal spring needs to be approx. 2X the stroke length, so it isn't practical for longer cylinders.

McMaster Carr carries single acting spring return cylinders to 12"
http://www.mcmaster.com/#standard-air-cylinders/=l94zkd

[twiegner]

Originally Posted by George C

McMaster Carr carries single acting spring return cylinders to 12"
http://www.mcmaster.com/#standard-air-cylinders/=l94zkd

This is exactly what we needed, thank you so much. Not quite sure why we didn't check McMaster, I guess we don't use them much for pneumatics. Though I do have to say that if this doesn't work we are going to but some serious thought into 1 of 4 choices. 1. Carrying more air tanks 2. Carrying a compressor 3. Alex's suggestion of adding another regulator or 4. Ditching pneumatics for a rack and pinion.

[Kevin Thorp]

Originally Posted by George C

McMaster Carr carries single acting spring return cylinders to 12"
http://www.mcmaster.com/#standard-air-cylinders/=l94zkd

Whoops... I commited the CD sin of posting an answer without double checking my info. Thanks George!

[Lil' Lavery]

Originally Posted by twiegner

This is exactly what we needed, thank you so much. Not quite sure why we didn't check McMaster, I guess we don't use them much for pneumatics. Though I do have to say that if this doesn't work we are going to but some serious thought into 1 of 4 choices. 1. Carrying more air tanks 2. Carrying a compressor 3. Alex's suggestion of adding another regulator or 4. Ditching pneumatics for a rack and pinion.

While a rack and pinion system is certainly a way to achieve linear motion given a rotational input, there are other viable solutions as well. If you want to move away from pneumatics for this application, perhaps you should also consider a crank, cam and follower, or whether you even need linear motion at all.