Re: exploding plastic storage tanks
 

Oddly enough, this may be due in part to a manufacturing defect, as we've had one of the fittings come out as well, and AM has a note about it on their site. http://www.andymark.com/product-p/am-2649.htm

Next time I have the chance, I'll take some temperature readings of the tanks themselves after a few compressor cycles and see if there's any sort of noticeable increase in temperature. I wouldn't be surprised if the right setup (one where the tanks are essentially next to the compressor) was able to pump a bit of heat into the tanks...

That's what I was thinking as well, but didn't know enough details about the situation to really say. I'm also not sure of how well the plastic tanks would handle heat cycling, specifically being exposed to temperatures outside of the operating range, then being brought back into the operating range before use.

Re: exploding plastic storage tanks
 

Also consider that PP's CTE is an order of magnitude more than steel or aluminum, if a plastic tank and mounting bracket were warmed up together the PP would strain against any metal mounting components, perhaps significantly.

Re: exploding plastic storage tanks
 

Before we call for a ban on all the plastic tanks, I think we really need to answer these questions. As far as I know PneuAire made the plastic tanks before Clippard started doing it. It was my understanding that Clippard released the 2013 plastic air tanks in response to teams using the PneuAire ones in the 2012 season.

We have used the PneuAire tanks (bought from PneuAire) without any failures for the past 3 years (only 2 in competition).

Safety is very important but we also shouldn't overreact.

Re: exploding plastic storage tanks
 

Here I feel the opposite.

Considering the failure mode (sharp plastic shards flying a high velocity) I would err on the side of caution. Until we can prove that the plastic volumes are safe in a FIRST environment (High impact, low technical knowledge, large swings in temperature) I would want to ban the plastic volumes for foreseeable future starting next year.


P.S. Has a metal volume ever failed in a dangerous way in FIRST (they have a much longer history)

Re: exploding plastic storage tanks
 

I'm not a plastics or pneumatics expert but I do know we don't ban all car seats when a single model is found to have manufacturing defects. Again I may be wrong and maybe the pneuaire tanks have a similar failure mode but lumping them together because they look the same seems like we are jumping to conclusions. I think we need more information.

Re: exploding plastic storage tanks
 

Allen, I understand where you are coming from but as someone who has had a 1 liter PVC pneumatic volume explode within 1 foot of me (thank goodness it blew out away from me) I will respectfully disagree here.

The dangers to anyone near one of these if it explodes, especially to bystanders, some of which may be children, is too high for my liking. Thus I say 'ensure it is safe and then we can use it'.

Re: exploding plastic storage tanks
 

I would agree... however the case I saw up at LSR (and prompted me starting this thread) was not due to a manufacturing defect - it was due to improper use and handling by the team.

From what I've seen of plastics in general, I'm not aware of any that could be use in this application that wouldn't have a similar failure mode. Then again, I'm a software engineer and not a chemist or material scientist. Still, it worries me.

Re: exploding plastic storage tanks
 

I understand that point, I also understand that we need to better train teams to the dangers of pneumatics and for them to properly care for their equipment. The team in this case was operating illegally since the screw had to damage the air tank and thus modify it. There is a reason for this blue box in the manual.

My point is that the PneuAir tanks have been in use on FRC robots longer than the Clippard tanks and I have never (doesn't mean it hasn't happened) heard of one of them failing do to misuse or defect.

Re: exploding plastic storage tanks
 

I agree. User error is significantly more dangerous than any potential manufacturing defects. I don't think there is any substantial hazard from plastic tanks that are used appropriately. This includes not over tightening the fittings, not deforming the body and minimizing stress on the entire tank.

Re: exploding plastic storage tanks
 

A pressurized, homemade PVC tank is incredibly different from an industry designed and rated part made of polypropylene. I get that these are scary, and I even wouldn't oppose phasing out / banning the white tanks with the screw fittings, but a blanket ban on anything that reminds you of something dangerous you were once near is a bit extreme.

As an aside, I'm interested to see what wrapping these tanks in gaffers tape would do for their failure mode. Obviously the pieces would rip through it, but the added resistance right as they start to gain velocity may be of more help than you'd think.

Re: exploding plastic storage tanks
 

Are you talking about all white plastic tanks with screw fittings or just the Clippard ones from 2013 that had a known failure and an optional recall? I really think we need to know more before we start making recommendations. This seems to be a pretty confusing issue, we don't know a lot about the differences between the different tanks (clippard, PneuAire, Andymark, etc.).

Re: exploding plastic storage tanks
 

Another means to address the safety concern of a light weight plastic tank would be a design that included either an integrated pressure release valve or a fail safe. Something that would release pressure in a known manner before catastrophic failure. This would allow lightweight tanks to continue to be used and eliminate the risk of a "user error" causing significant harm.

Re: exploding plastic storage tanks
 

For those teams still using the white Clippard volume storage tanks from last year, you should read the FRC Blog linked here dated January 30, 2013.

There are very specific instructions included on the safe installation of the fittings on these tanks. I'm not sure if Clippard will still replace them, however I personally know the Clippard family and company and I know they want to protect the safety and health of every FIRST participant, spectator and volunteer.

We currently use two of the new black vst from Clippard and are very pleased with them.

edit - Allen beat me to the post above...

Re: exploding plastic storage tanks
 

First this is a great discussion with a lot of points on all sides of the issue.
I do have to agree with JesseK that if a simple and reliable solution is not identified FIRST will have no option but to go back to the metal tanks.

I would be great if we could get consumer reports, mythbusters or someone of that quality to test various sleeves/coverings.
I am not a physics person but from an intuitive point of view a sleeve/shroud of some kind should reduce the danger.

User error is the real issue.

Re: exploding plastic storage tanks
 

A relief valve won't solve the issue causing failures. Failures aren't caused by over pressurization in most cases (assuming in competition and with passed inspections). The problem is a degradation in pressure capacity due to mishandling the tanks (over tightening, improper mounting, etc.). What do you do when a tank fails at 100 PSI? 80? 60? If you put a crack in the right spot or damage a wall on a tank, any of these pressures could cause a failure in the right circumstance. The white Clippard tanks are great tanks, they just have very specific instructions for their use that are tough to follow perfectly. But they have a really phenomenal warning alarm when used improperly in the form of an explosive blast that will wake the neighbors and potentially kill you.