For f*ck's sake, stored energy = pressure x volume. Daniele seems quite aware of this concept, unlike you. He's proposing pressurising a water filled container with an insignificant volume of air.
Tim
She?? I think you'll find she's a he.
He said a 10 litre tank, that would be filled with water first, leaving a tiny volume of air in the pipework.
I imagine any fool would know that motorcycle tyres are not inflated to 100 psi. A "bike" in this case is a push bike.
Tim
Many, many years ago I worked in a lab where a test rig had a section of glass pipe in it. This had been bound with many, many layers of sellotape in the thought that this would provide containment if it cracked. Someone who didn't believe it took one off site, pressurised it, and put a 0.22 bullet through it from a safe distance. The tape made no difference at all to the remarkably wide spread of debris.
You havn't said how old the kids are, but I think what they are doing could be very very dangerous indeed, quite apart from being seriously illegal.
Yes. I have a motorbike. That is why I queried your statement;
" Blowing up my bike tyres is far more dangerous. Much bigger volume and routinely filled to 100psi."
From this it seems that either you have a (motor)bike with tyres inflated to 100psi. or a (push) bike with tyres of much more than 10 litres capacity or you're the fool.
Which of the above 3 statements is true?
ICBW but I think you'll find that Daniele is the female variant of the name.
... in which case the volume is nowhere near 10 litres.
Andy
Probably one of the less hazardous activities discussed so far. I'm not greatly concerned what she/he lets the kids do.
However, I have a shed full of copper tube and valves and could easily assemble a test rig that would withstand these pressures. I also know enough to fit an air-vent valve at the high point and have suitable valves. You're assuming Daniele has both these things. Since he/she did not know how to connect valve (washing machine!) to tank, I assume he/she doesn't.
Although I could, I still wouldn't.
The proposed test rig, would probably have a large volume of water and a small amount of air at the top. Similar to a bottle of fizzy drink, or a champagne bottle, yes? Although at a lower pressure.
I'd suggest you Google for "eye injury", "soda bottle", "champagne bottle" and similar combinations. Lots of such unfortunate incidents detailed on the internet.
If i was the OP though, I'd be more concerned about the contents of the Firearms Act 1968 and later amendments.
I'm a little uncertain whether he/she gets the (mandatory?) jail sentence or whether it's the kids that get a criminal record each.
On 07/07/2013 23:03, newshound wrote: ...
Colin Bignell
+2 And an unusual name, posted on the internet, in connection with such seriously illegal stuff. I'd suggest you dismantle whatever the clever little darlings have put together.
Where does this mythical 10L come from?
Are you saying that a 10L vessel *filled with water*, when pressurised with air, contains the same stored energy as an empty vessel pressurised with air?
My point was that my bicycle tyres when pumped up with air have more stored energy than would be present in a pre-filled 10L expansion vessel (assuming the diaphragm has been perforated enough to remove air from behind it).
Tim
I worked in a High Voltage cable Co. for a while .... used to be a common prank to connect a piece of galv pipe vis flexible hose to the standard compressed air outlets (all round the place)
Sticky some butyl rubber bedding down end of tube and fire by opening air valve ... not sure what full air pressure would be ... but it could certainly fire across factory ... and gave doughnut shaped bruises if they managed to hit you.
H&S not particularly a concern then.
From the original post, where it is written;
" and someone must have heard, because yesterday evening in the lane behind our house I found a 10-litre expansion tank."
No. I am saying that a 10l vessel, filled mostly with water, and with some air gap at the top, quite probably contains enough energy to do serious injury, especially if pumped up to a ( frankly) incredibly stupid 100 psi or more, using a cheap gauge of unknown accuracy, especially if the test apparatus ( assembled by children, using scavenged plumbing/hose fittings) should happen to come apart under presure.
The vessel filled with water and with a small air gap at the top is compared above to a 2l pop bottle, which is known to contain enough energy to do serious injury, although it is at a much lower pressure.
It's not a tyre. Tyres are expertly designed for their application. It's an air cannon bodged up by kids.
Why do you assume that? Once you've wrecked the diaphragm I'm sure it would be easy to fill and cap. Then you use the handy Schrader valve to pressurise. The gas volumes involved are going to be tiny with just a modicum of care.
I would question whether testing to 100psi is necessary but done with a knowledge of physics and a little due care, I see no reason why it couldn't be done safely with a tiny quantity of air. Of course pressurising with a fluid would be better but how many of us have a method of pressuring something with a liquid beyond mains tap pressure (which could be way too low to be useful) AND measuring the pressure just kicking around the house? A bicycle pump though is something that most people have.
Lets assume that there's going to be a little adult supervision eh? The kids will learn a bit of practical physics, get some tool handling experience and will probably be happier and better prepared for a real life than those handed a gameboy.
You seem to be a "worst case scenarioist". How do you get out of bed in the morning?
Tim
...
If you pressurise 10 litres of water to 100psi with air at room temperature, it will dissolve around 1.3 litres more air than it can hold at atmospheric pressure, in addition to any air space.
Colin Bignell
And this dissolving is instant? For the duration of a pressure test I doubt it'll make much difference to the stored energy.
Anyhow, I've just pressurised an old expansion vessel that I had kicking around. I tore a hole in the already knackered diaphragm, filled it to the brim and got it up to 80psi very quickly with just a few strokes of my track pump.
I had to stop there as plastic hozelock fittings aren't really much cop over 60psi and they started leaking. ;-)
Still, I sense a pointless project coming on, if for no other reason than to annoy the health and safety weanies on here who clearly never did anything remotely adventurous with their kids. My dad taught me how to make gunpowder. Now that *was* dangerous. ;-)
Tim
There you go, your scheme unravelled in two words; "Let's assume.....".
I have a better idea. Let's not assume anything.
The OP is the responsible adult and he/she doesn't seem very well informed on such stuff.
Besides which, if she's got any sense, the thing has been dismantled and dumped before Plod breaks the door open at stupid o'clock. It gives the armed response lot an outing and a firearms conviction always sounds good, even if it's bollocks.
Yeah, That's a bummer. Probably a legacy of where I've been. A bit of pressure testing witnessing, unit first aid instructor and civvy FA qualifications.
So I was usually the one who got the nice jobs when assumptions proved to be incorrect. It makes one more cautious.
We assume things about posters on here all the time. Why heaven forbid, even advice about handling electricity and gas is given out here without always knowing the competence of the recipient.
Feel free to have the last word though, you seem like the sort of person who just *has* to have it. I'm bored silly by this conversation. I've done the test, I'm still here. Pressurising a completely water filled expansion vessel with a track pump is very undramatic.
Tim
On 08/07/2013 15:10, Tim+ wrote: ...
Only if contained, say in a 10 litre expansion vessel, when ignited.
I used to make guncotton under the bench in the chemistry lab at school, but I wouldn't suggest anybody else doing it. The difference is that most people simply don't realise just how dangerous compressed air is, but they do have an idea that explosives are.
Colin Bignell
You don't have to assume much, the OP asked for advice stating she knew little about it.
The advice was given with mention of how potentially dangerous it was and the illegality.
Splendid; does this prove that all such second-hand tanks are safe and can take 100psi?
You can have the last word, if you please. Nothing will change my opinion though. It could be quite dangerous and you've been giving out some seriously stupid advice suggesting it isn't and kids should be allowed to lash something up to do it.
You've just been writhing around for the last few posts, trying to qualify what you'd said and make it appear less stupid. I just happen to know more about presssure testing. And the construction of expansion vessels.
He, of course.
And much appreciated it is.
As it happens, the police have already had a look at it and given it their approval.
Apparently while they were out in the lane making it, the police came by and said "We're just checkin' what's goin' on but we can see you're all tidy boys" ("tidy" is a kind of South Wales general expression of approval).
They didn't explain they were planning to fire missiles with it though.
Daniele
Oh, you didn't say it was *Wales* .....
And sending AAA batteries 100 metres must be well beyond the permitted airgun energy limit.
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