Are these tanks legal?
 

I know the white Clippard ones are illegal, but we are unsure if these ones are. Unfortunately, they are all unmarked. It would help if we could determine what these are, whether or not they are the white Clippard tanks, since we heard not all white plastic tanks were illegal.

Re: Are these tanks legal?
 

I know some people will argue otherwise, but illegal or not, I would not use ANY plastic tanks on my robot. The failure mode is simply too dangerous.

Re: Are these tanks legal?
 

If they are unmarked, you can't provide a part number and related specifications to show that they are rated to the required pressure, can you?

so I expect they are not legal just because of that.

Re: Are these tanks legal?
 

The RI will not like them. Don't use it. That's my advice

Re: Are these tanks legal?
 

Without a brand it's sketchy imo. Breaking $50 on new black Clippards could save you a lot of headache (or just heads in general).

Re: Are these tanks legal?
 

Please verify the source of the tanks, they look similar to the pneuair tanks that we have been using for 3 years and other teams have been using since 2010. I've use dozens of these from pneuair and never had an issue. The only explicity illegal air tanks are the white clipplard brand air tanks. All other tanks that meet all the rules are legal but it is in the team to show documenation proving it.

Re: Are these tanks legal?
 

Where did you get the tanks? They look a lot like the tanks that AndyMark sells which have no markings on them which are legal.

Here is one of the 3 unmarked tanks they sell. http://www.andymark.com/product-p/am-2477.htm

Re: Are these tanks legal?
 

More specifically, the white Clippard tanks with the green lettering. (Do you have black ones? If yes, use those)

A good rule of thumb is, and this is for any COTS item with a not easily recognizable part number, keep a copy of the invoice or receipt from where it was purchased. A data sheet is even better to show the inspector.

Re: Are these tanks legal?
 

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?

Re: Are these tanks legal?
 

The failure mode of plastic tanks is a catastrophic release of high pressure air that quickly accelerates large sharp plastic pieces. These pieces, with the pressure FIRST allows, could shoot more than 100 feet (IE: into the crowd).

I have been close to a plastic (non-first) 1 liter volume that failed at 100 PSI. I can tell you I am lucky to be here (the volume blew out away from me).

The only way I'll have plastic pneumatic volumes on my teams robots is if it is completely enclosed in a box (to absorb as much of the energy as possible) and even with this setup, I would be reluctant to do so.

Re: Are these tanks legal?
 

If the tank has no markings, then you can't prove the white tank is NOT the disallowed tank. Thus I would reject is as an RI.

Are there any PSI markings on the tank? If you can't prove the tank can hold 125 PSI safely, then that is another reason to reject the tank.

Re: Are these tanks legal?
 

Hi!

We have been using these tanks since they went on sale back in the day. I can't tell from here the exact volume or port sizes your tanks feature, but searching up am-2477, am-2478, and am-2479 should give you relevant technical specifications that would help guide all but the most skittish RIs at your events. I also recommend getting some masking tape and writing "NOT CLIPPARD TANKS, PLEASE STOP COMING OVER TO OUR PIT AND TRYING TO TAKE OUR TANKS" because in my experience that will save you some stress.

It's your job as a team to make sure your robot is easy to inspect just as much as it is an RIs job to know what they need to look for when inspecting a robot.

I believe Allen is an LRI at various events. In this thread he's probably the foremost authority. I think it would be super if everyone else in legality threads could either feign honest understanding or step back instead of fearmonger, but I'm not a cop and can't tell people what to do.

Re: Are these tanks legal?
 

The tanks in the picture and the disallowed clippard tanks look nothing a like other than their color and that they are air tanks. The team will need to prove their legality but just dissallowing them because they are unmarked is not a rule.

Re: Are these tanks legal?
 

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.

Re: Are these tanks legal?
 

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.

Re: Are these tanks legal?
 

I do not know Allens background when it comes to Pneumatics, but I do know mine as 7 years as a manufacturing engineer with pneumatic devices.

First off -- when someone asks what the failure mode is, explaining it to them is not fearmongering.
Second -- When people state that they will not use, or will only use under specific criterion, an object due to safety reasons that is their opinion, justified or not, and again not fearmongering.

I know what the failure mode is. I have seen the failure mode UP CLOSE. When I say I'm lucky to be here, I mean it.

FIRST has chosen to make these legal, that is their choice. My decision to put a box around them is an additional safety feature that I CHOOSE to implement as a safety for the audience and to protect the volumes from "robot-to-robot interaction".

If you CHOOSE to ignore my advice, that is your choice. I hope that you never see the repercussions of that choice.

JM(NS)HO

Re: Are these tanks legal?
 

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

Re: Are these tanks legal?
 

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

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.

Re: Are these tanks legal?
 

The issue with the banned white Clippard tanks was that they had threaded ports on either end and if the brass insert was over tightened, the tank could (and did) fail at the threads. I cant tell by the picture, but if it uses threaded ports, as a RI I would fail it even if it were not Clippard and was demonstrated as rated to 125 psi.

Yes, bring documentation of where and what you purchased.

Re: Are these tanks legal?
 

Really hope we never go to an event where you are an LRI.

If a team has built a robot within explicit and objective parts of the rules (specifically 4.11 and R77 in your case) and you fail them anyway, you're doing an incalculable disservice to that team, Robot Inspectors, and FIRST. I guess you can try to call it an R9 since that rule in theory is pretty wide open, but its implementation is not to make illegal things that are explicitly legal.

I'm not a robot inspector, judge, referee, etc., but myself and my students can in fact read official FIRST documentation and we would really appreciate it if those with power to decide whether or not we are competing within the bounds of said documentation would also read it.

Of all of the absurdity that fills these digital walls, this kind of attitude stands heads and shoulders above in what not to do.

Re: Are these tanks legal?
 

This emphasized statement bothers me ( and this, coming from one whom is distrustful of plastic volumes).

1> Are these items allowed per the rules? Yes.
2> Does a Plastic Volume with threaded ports have an inherent risk? Yes.
3> Should an LRI automatically ban that item? No. (s)he should look at the implementation and decide if enough has been done to mitigate the safety risk and then make a judgment call.

It's the same when you are using sprockets and chain. It is in the design and implementation that makes it safe of not.

Re: Are these tanks legal?
 

What testing have you done that proves that it is any threaded port on a polypropylene tank that can cause problems? Have you ever seen, heard of, or documented any plastic tank failures in FRC other than those by the original white Clippard tanks?

If I make a black plastic wheel and it happens to break apart and throw shrapnel when spun at 100 RPM should we ban all black plastic wheels? That would be the same thing as banning all plastic tanks. We specifically know that the Clippard tanks had manufacturing problems yet some people still hold it against every other plastic tank on the market, I will never understand this. I hope to keep everyone safe as well and individual teams should decide what is safe for them but the Robot Inspectors are there to enforce the rules as they are written. It would be easy for the GDC to ban all plastic air tanks with threaded fittings if they believed they caused a risk, they haven't; there for they are legal and should be ruled that way by all robot inspectors unless other factors are at play (tanks clearly damaged or showing cracks, etc) that lead you to believe they are unsafe.

Re: Are these tanks legal?
 

Allen, if someone went out and did failure analysis of black plastic wheels and found the same failure mode was present in any plastic wheels, then a ban should absolutely be considered. Similar, if industrial regulations dictated that black plastic wheels should only be used when fully enclosed, the same would apply.

Re: Are these tanks legal?
 

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...

Re: Are these tanks legal?
 

If you can't see, it is threaded inside. However, I don't think I can find the receipts/documentation for what it is since I found it lying around in some bins. I think we're just going to use metal tanks.

Re: Are these tanks legal?
 

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?

Re: Are these tanks legal?
 

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.

Re: Are these tanks legal?
 

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...

Re: Are these tanks legal?
 

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.

Re: Are these tanks legal?
 

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

Re: Are these tanks legal?
 

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.

Re: Are these tanks legal?
 

First of all, I am not a LRI, just a lowly RI and of course it would be escalated.
Second, there are always tanks available at competitions so replacing a questionable tank is not an undue hardship on the team. A box around the tank is also a safe option.
Third, the blue box on R76 says "Consider pneumatic components sacred". That is stronger language than sprockets and chain. The tank will have a torque specification on the fittings, how does a RI verify that it has never ever been violated?
Last, the push in fitting tanks do have a limited life, but the failure of the fitting results in the tube being expelled in a safe manner.

I personally think the risk of using the tank in question is too high and would not use it even for practice.

Re: Are these tanks legal?
 

We always use them. Not the white ones, but we had 5 of the black tanks on our robot last year and that robot that went an entire season, plus two off-season events, and numerous outreach activities without a problem. Just check that your wiring is correct, the compressor shutoff switch is fully functional, and you'll never have a probem. (yeah, there's white ones that are perfectly okay, but if you can't tell the difference between a good white tank and a bad white tank, and you still can't tell after doing some research, you're better off just using something else) We still had one of the bad white tanks for quite a while, and we didn't realize we still had it until someone found it in the bottom of a scrap bin last season. After checking its model number on line and realizing it was one of the failure-prone tanks, we got rid of it immediately.

I was at an event where one of those tanks exploded. Fortunately, I wasn't nearby, but that bang could be heard throughout the entire building. Personally, if I had even the slightest feeling that one of the air tanks might be faulty, I probably wouldn't use it purely out of superstition. However, this doesn't mean those tanks are objectively against the rules, and it also doesn't give an RI the ability to fail you unless the tank is actually not legal. However, with such an ambiguous marking, if those tanks were to be used, it would be wise to figure out what they actually are, and ensure that the documentation legitimizing their use is on-hand.

Re: Are these tanks legal?
 

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.