well you're never going to know it's safe really, which is why you have a look at it and decide.

If a n00b turned up with something like Jolt I'd be more than a little bit concerned about it being able to keep its teeth on the bar, etc!
Knowing that Nick has put considerable thought into the design, construction, and parts chosen does make a big difference - even though I'm sure no manufacturer would give a guarantee on those parts in this particular use.

The complexity of even a simple pneumatic setup will deter most first time builders I think, but there will always be a question mark, and no amount of rules can change that.

Jeff was always very careful with El Bravo, and put a lot of work into making sure that the bottles were strengthened adequately, even though they can theoretically survive the pressures they were running at.
Even that system can be dangerous though, and someone building one carelessly could very easily be injured, just the same as a CO2 system - although possibly more likely due to the larger number of home built parts.
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The Engine Whisperer - fixer of things

I agree that a new bot from a new builder will still need a tech inspect and I agree that a noob would be scary building a high KE, but in this thread we need some quantifiable guidelines for people to follow when building your style of system.

What pressure would you recomend that the "fusable hose" must fail? How would you want this proven?
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So even the rain that falls isn't actually going to fill our dams and our river systems

personally I'd want the "fusable hose" (good name for it!) to be a last resort part of the design, but from what I've seen if it's the usual black rubber vacuum line type of stuff I think it's pretty safe to assume it'll blow before any decent ram.

I don't think proving the burst pressure of the hose is that necessary as long as it's obviously a low pressure hose and it's been used in the right area of the system (ie, somewhere that is under the full system pressure when in use).

Do pressure relief valves usually have to be demonstated to work at the right pressure at competitions?
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The Engine Whisperer - fixer of things

Ususally no, but it can be demanded and tested if the situation warrants it.

frangible would be more "accurate" and sounds cooler i think ;->
http://en.wikipedia.org/wiki/Frangible
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Mechanical engineers build weapons, civil engineers build targets

I have got some hose that is rated for arond 300 psi. It will take 1000 psi for a long time (hours) before it bursts. We don't want a kid turning up with macro lines and calling them low pressure. We need a rule that we can use to measure the bot against and say yes that complies or no it does not. We need a firm definition of low pressure hose. Does it fail at 20 psi, 50 psi or 100 psi?

We could always use a comercially available pressure relief device such as those found on air compressors.

BTW FRA rule on PRDs

"Do pressure relief valves usually have to be demonstated to work at the right pressure at competitions?"

8.9.
PRD(s) should be readily accessible and must be removable for testing purposes.
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So even the rain that falls isn't actually going to fill our dams and our river systems

Philip,
PRD's are not normaly tested at every event, but an E.O. can require a test to be carried out at any time.
So the rule was written to cover the "We reserve the right to test it at any time and we don't want to have to disassemble your robot in order to do it!" situation.

Geoff.

Thanks for your input, Geoff. It is good to receive advice from people with lots of experience with CO2 flippers.
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So even the rain that falls isn't actually going to fill our dams and our river systems

Just to play the devils' advocate here, what if Andrew used high pressure steel tube and fittings rated for way more than the sodastream bottle could supply? What would fail in an over-pressure situation and how would it fail? The UK guys think the tank is limited to 200 psi so if the ram is rated for more than that (very likely), then the next thing to fail is likely to be the exhaust valve, which will not cause much, if any, damage.

I can't recall how the sodastream bottle attaches to the gas system; I assume its using the original sodastream fitting?
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Are you talking about Woody saying that he thinks there is a 200 psi PRD in the line? I don't think that Woody has ever seen a Soda Stream (sic).
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So even the rain that falls isn't actually going to fill our dams and our river systems

nah there's an extra pressure relief in the sodastream machine, which also works as a vent valve as you remove the glass bottle.

The sodastream uses a nylon tube with a compression fitting into the nylon valve body.
I replaced the nylon tube with the same diameter copper tube, so I could connect to it easier and extend the length. It then connects to the vacuum line via a hose barb fitting.
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The Engine Whisperer - fixer of things

Hi Philip,

Thanks for the kind comments, but I'm no great pnumatic expert.. There are people that know far more than I.. Woody for one! (Now, if you want to discuss the black art of building high speed spinners.. different matter!! )
If you want a difinative answer on your Soda Stream question e-mail a guy called Mike Lambert at... mike.lambert1@ntlworld.com He is the FRA pneumatics consultant and over here his word is law!!
Part of my Job in the FRA is to explanain and if required, enforce the build rules.
Slightly off topic, will be an honour to meet some of you in San Fran next June and I really hope Team Australia will get the chance of some deep and meaningful comabat with Team Europe!
Just one word of warning guys, look out for the G.I.P (girls in pink) AKA Team Pillow Torque! They take no prisoners!! (in or out of the arena!! )

Back On topic.

Geoff

I've uploaded a pic for people that are unfamiliar with Sodastreams and their fittings.
http://www.robowars.org/forum/album_pic.php?pic_id=1310

I've tested a different sodastream prd and came up with a relief pressure of 100 psi ....... I couldn't find the third relief valve that I'm sure I have somewhere!... to make a 3rd comparison ..... perhaps someone else can test one so a definitive manufacturers pressure rating can be deduced.

As DumHed said ........the 200 psi of my first test appears wrong ......100psi seems a better test result.

@ Nick ALL CO2 Bottles that contain liquid have approx 800 psi pressure in them @ room temperature and pressure.

Cheers Woody

Edit :- Pic also shows a pressure regulator setup that I used to test the Sodastream relief valve .........it can be seen screwed into the regulators body........ the other brass pressure relief valve is laying between the bottles.

quote:

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Just one word of warning guys, look out for the G.I.P (girls in pink) AKA Team Pillow Torque! They take no prisoners!! (in or out of the arena!! )

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I think we can say Woody has seen a few Sodastreams...

My point of view is that if a part fails in a way that doesn't cause danger, then who cares? If the tank was to explode, that's a big deal with shrapnel sprayed around the area. If plastic hose splits, it is not going to hurt anyone except the builder's pride. We need to rate all the parts and ascertain their typical failure ratings. As long as the first few failures are not dangerous then we can say there is an extremely low chance of injury with low-tech sodastream powered bots.

The trick will be to make sure the rules ensure the failure points are all at harmless points...
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion