Are these tanks legal?

[AllenGregoryIV]

Originally Posted by cgmv123

It's not a rule, but the introduction to the robot manual says the burden of proof is on the team to prove the legality of any part.

That said, if I remember correctly, the illegal Clippard tanks very clearly say "Clippard" on them.

Correct that is what I'm saying.

Coastal Pneumatics seems to have bought out Pneuaire who we used to purchase from but they seem to be the same tanks.

Here is the data sheet on the storage volume chambers we have been using for several years without incident. https://www.coastpneumatics.com/pdf/RC%20canisters.pdf

I've posted this in other threads, I've have never been told of any plastic tank failures other than the white Clippard tanks. It's also my understanding the white Clippard tanks were the first plastic air storage devices that Clippard produced and they made them specifically for FRC. Clippard is an awesome sponsor of our program and they have gotten the design correct with their updated black tanks. Other companies that have been producing white storage volumes for many years have not had the same issues as the original white Clippard tanks.

Teams please keep track of your purchases and have data sheets ready for your inspectors.

[IronicDeadBird]

Seems sketch and unmarked to the max...
If you don't know what something is why would you put it on your robot?

[JamesCH95]

To answer OP: you need the proper documentation to prove the parts' pressure ratings to an inspector. Cut and dried IMO.

Originally Posted by trumpthero786

Hmm I can't imagine using anything BUT the plastic tanks, but you have far more experience than I do. What sorts of failures have you seen in them?

I did a hefty amount of research into this a few years ago. There were a few root causes:

-The white Clippard tanks had casting voids near their threaded fitting area, weakening a key structural area
-If the threaded fittings were over-tightened cracks could be initiated in the tank
-If tanks were subjected to rapid or extreme temperature cycles they could become prone to failure (plastic shrinks more per unit temperature than the metal fittings screwed into them, generally speaking) one team had a tank burst when pressurizing a robot
-Overly aggressive mounting solutions (like hose clamps that were tightened too much) put undue stresses in the outside of tanks, increasing the chance of failure

The black Clippard tanks have improved mold design to stop voids, molded-in push-to-connect fittings, and are a more ductile plastic. They are a vast improvement over the white Clippards that were the focus of several (many?) failures. My own un-scientific destructive testing convinced me that the black tanks are considerably more robust than the white tanks.

The penalty of failure with plastic tanks is high because (if they fail) they generally undergo brittle failure, that is to say they make shrapnel. A failure in one plastic tank might cascade to adjacent tanks. Metallic tanks (if they fail) generally undergo ductile failure; there no shrapnel, or very little shrapnel.

What are the risks of any tank failing? The plastic shrapnel is sharp and could hurt someone (wear your safety glasses near any active robot) as it gets flung around 30-100 feet. Perhaps the more traumatizing danger (IMO) is the potential for hearing damage.

Having said that, there have been few, if any, failed tanks outside of the white Clippards. There have been no failed metallic tanks that I know of.

Considering the penalty of failure when using plastic tanks our team chooses not to use them. We recognize that many teams have successfully used tanks in the past. However, having done destructive testing on both plastic and metallic tanks, we have not found the compromise in penalty of failure to be worth the weight savings.

The only argument against metallic tanks that I've heard is weight. Only using metallic tanks, we have not had an overweight robot in at least 5 years, all of which used pneumatic systems. Careful selection of metallic tanks can reduce the weight penalty associated with them, and careful pneumatic system design can reduce air usage. IIRC 558 had an aluminum tank (2 years ago?) that was lighter and easier to package than the equivalent in any plastic tank.

[MrBasse]

Originally Posted by JamesCH95

...The black Clippard tanks have improved mold design to stop voids, molded-in push-to-connect fittings, and are a more ductile plastic. They are a vast improvement over the white Clippards that were the focus of several (many?) failures. My own un-scientific destructive testing convinced me that the black tanks are considerably more robust than the white tanks...

I'll take this opportunity to remind teams that push-to-connect fittings have a lifespan. The barbs are designed to grab a hose one or two times. They are typically rated for ten cycles without failure. Anything beyond that and hose retention is a gamble that you have to determine the risks and rewards of. Since the fitting is molded in, so is the hose barb. I won't even get started on the o-rings that are non-serviceable...

[ToddF]

Originally Posted by MrBasse

I'll take this opportunity to remind teams that push-to-connect fittings have a lifespan. The barbs are designed to grab a hose one or two times. They are typically rated for ten cycles without failure. Anything beyond that and hose retention is a gamble that you have to determine the risks and rewards of.

This is news to me. We use SMC one touch fittings. I'm unable to find any such limitations on connection cycles. Can you point me to your reference?

[Tristan Lall]

Originally Posted by ToddF

This is news to me. We use SMC one touch fittings. I'm unable to find any such limitations on connection cycles. Can you point me to your reference?

I'm not sure of such a reference, but there are definitely many kinds of available push-in fittings, with different performance. I think it would be difficult to generalize. (Some are very tight and dig into the tubing, others are more easily releasable.)

The type of tubing (material and dimension) also matters—most styles are operable with polyurethane tubing, but there could well be non-obvious exceptions.

[MrBasse]

Originally Posted by ToddF

This is news to me. We use SMC one touch fittings. I'm unable to find any such limitations on connection cycles. Can you point me to your reference?

I worked for Parker Hannifin for several years designing products in their brass fittings division and we utilized a large group of their PTC fitting line in our product. I'd have to dig to find it if I still can, but the rating used to be on the product catalog main page. When you insert the tubing, the proper method is to insert fully and they'll tug to seat the barbs. This deform the barbs a little bit. After being done a few times the barbs no long hold a perfect shape. The metal that makes up the barb itself is only a few thousands thick and won't hold shape for long when being deformed back and forth. I'll see if I can find the spec and get back to you.

The orings just get torn up if your tubing isn't cut properly...

[Al Skierkiewicz]

Having been involved at ground zero I can tell you that not all failures were at the port, not all were due to voids and not all were due to overtightening the hardware. There were a lot of issues. One of the most catastrophic I investigated was on a robot where the team had used metal hose clamps to mount the tanks. The inside of the clamp hardware produced stress on the side of the tank and that was where the failure occurred. Think about the Pillsbury dinner roll package when you press on a seam. This team had severely distorted the outside of the tanks. Inspectors have to make the decision to allow or not allow certain devices on robots in the interest of safety to students and volunteers. Why would anyone put an undocumented part on their robot. If you can't determine where they came from and what the actual part number is, then neither can we.
Please don't use metal hose clamps when ty-wraps work as well.

[JamesCH95]

Originally Posted by Al Skierkiewicz

Having been involved at ground zero I can tell you that not all failures were at the port, not all were due to voids and not all were due to overtightening the hardware. There were a lot of issues. One of the most catastrophic I investigated was on a robot where the team had used metal hose clamps to mount the tanks. The inside of the clamp hardware produced stress on the side of the tank and that was where the failure occurred. Think about the Pillsbury dinner roll package when you press on a seam. This team had severely distorted the outside of the tanks. Inspectors have to make the decision to allow or not allow certain devices on robots in the interest of safety to students and volunteers. Why would anyone put an undocumented part on their robot. If you can't determine where they came from and what the actual part number is, then neither can we.
Please don't use metal hose clamps when ty-wraps work as well.

Not too dive off into the weeds too far... but I recall years (2010?) where zip-ties were specifically prohibited from being used to mount storage tanks. That practice does appear to be legal this year. What do you recall of past years' rules, Al?

Zip-ties aside, there are many options with which to secure air storage tanks (I like vibration damping loop clamps): http://www.mcmaster.com/#pipe-routing-clamps/=115wm73

[Al Skierkiewicz]

James,
I don't recall that rule. There were times when plastic tanks were not allowed, and there were restrictions on how much storage a robot could contain. Heck, I even remember a time when pneumatics were not allowed.

[ToddF]

Originally Posted by MrBasse

I worked for Parker Hannifin for several years designing products in their brass fittings division and we utilized a large group of their PTC fitting line in our product. I'd have to dig to find it if I still can, but the rating used to be on the product catalog main page. When you insert the tubing, the proper method is to insert fully and they'll tug to seat the barbs. This deform the barbs a little bit. After being done a few times the barbs no long hold a perfect shape. The metal that makes up the barb itself is only a few thousands thick and won't hold shape for long when being deformed back and forth. I'll see if I can find the spec and get back to you.

The orings just get torn up if your tubing isn't cut properly...

I just got off the phone with a Parker Applications Engineer. Consider my mind officially blown. Parker is completely unwilling to stand behind the reliability of connections made with their PTC fittings. They say the fittings are tested to an ISO spec of FIVE make and break connections and are not willing to publish reliability data beyond that test. I work at NASA Langley Research Center as a contractor, and reliability of pneumatic connections is a BIG deal. I now need to make some calls to our pressure systems safety office. This has the potential to turn into a big hairy deal.