Compressed air bottle for small pneumatic purposes

[Needleplayer]

I also saw the episode of Mythbusters. The tank were not completely filled and the heating of water under pressure, given a super heated steam. So hot steam has many times the energy than compressed gas, and the more dangerous. Normally, a water heater is completely filled with water and will not achieve the result Mythbusters achieved.

Testing of pressure vessels, often using a water filled completely. If the tank does not withstand the pressure, it will just crack and do significant damage.

Old steam-powered trains and boats, used low pressure steam (can not remember which pressure). There was major damage to the safety valve was inoperative and the boiler exploded.The safety factor is much higher for the pressure vessel for gas rather than liquid.

Be careful and use the tanks intended for gas (air).

[Sir Cumference]

Testing of pressure vessels, often using a water filled completely. If the tank does not withstand the pressure, it will just crack and do significant damage.

Exactly.
Water is incompressible (for practical purposes), meaning that you can not store energy in "compressed water".


Gases are compressible, and the work you do compressing them, is released when you release the pressure. If it is released slowly and controlled, it can perform an action in a pneumatic cylinder, a turbine or other form of pneumatic motor.
If the pressure is released suddenly, you will have an effect like a rocket or even an explosive effect where the container ruptures and fragments are accelerated by the pressure.

I also saw the episode of Mythbusters. The tank were not completely filled and the heating of water under pressure, given a super heated steam. So hot steam has many times the energy than compressed gas, and the more dangerous. Normally, a water heater is completely filled with water and will not achieve the result Mythbusters achieved.

Not quite.
Yes, a water heater is normally full, but it is not closed. It is connected to the piping, and it has a release valve.
When it is filed with cold water and heated, the water will expand, and if it could not release that thermal expansion, either through the piping or through the release valve, the water heater would be split by the hydrostatic pressure.

Had Mythbusters filled the heater completely, plugged the tubes and disabled the safety valve, the heater would just have cracked in a very boring way at a much lower temperature.

But by filling it partially, they allowed for the thermal expansion, thus having only a small pressure increase from that side.

What made it really fun was the other factor: Heating

Now you add energy in the form of heat, not just mechanical compression. As the temperature rises, so does the vapor pressure of the liquid. But it doesn't boil, because the boiling point is rising with the pressure.
We add more heat, and the pressure rises and we go on heating.....

Once the tank bursts from the pressure we have a very interesting situation. There is the immediate pressure in the tank, but there is also a superheated liquid that will flash into a very large volume of steam, adding significantly to the destructive force.
The effect is called a "boiling liquid expanding vapor explosion" (short "BLEVE" .... some say it really is an acronym for "big loud explosion very exiting")

Boiler explosions are normally very destructive, and a lot of accidents during the industrial revolution led to most countries having legislation concerning "pressure vessels" of all kinds.

- Cold, completely filled pressure systems are normally not particularly dangerous in case of malfunction (hydraulic systems operate at very high pressures, but accidents are rare)
- Compressed gas systems can make a mess
- Heated pressure systems with gasses and liquids can make a horrible mess.


Boiler explosions result from several factors.

- during use, there will be an erosion on both the inside and the outside of the boiler
- if water containing minerals is used, boiler scale will form, isolating the hot wall of the boiler from the (relatively) cooler water, leading to hotspots
- low water level will lead to overheating of the walls
- metal looses strength when heated, and will fail http://www.engineeringtoolbox.com/metal ... _1353.html

If the boiler is worn out, and it then is low on water or covered by scale, the boiler is likely to explode even if it has an operational safety valve.

Of course, a blocked safety valve could lead to the explosion of an otherwise perfectly healthy boiler.

Be careful and use the tanks intended for gas (air).

Again, I agree, and disagree.

I totally agree, that whenever you play with something that has the capability to kill or maim you, be it cars, guns, pressure vessels, a pet jaguar or self bondage, it is paramount to be careful.
But what medium the tank is designed for, has little concern compared to what pressure it is actually rated for, what pressure it is tested at and the physical state of the tank.


If the pressure vessel is in good condition and is used at or below the rated pressure (which is well below the test pressure, which is again somewhere under the expected burst pressure), an exploding tank should not be a real worry, compared to the possibility of the house catching fire or grandma visiting while you are locked in the pneumatic stocks.....

[mfx]

Note if you are intending to use commercial gas cylinders and try and re-fill them many (depends on type and country) have non-return valves and some also have excess flow valves (mostly on propane cylinders). The non-return valve is there partly so that back pressure in a mixed gas system can't force other gasses into the cylinder but also so they can't be re-filled without a special fitting (not hard to make if you know what you're doing though ) and the excess flow valve is there to act like a fuse, in the event of a burst hose it shuts the gas off so if your take off rates are high then it will trigger. Also re-filling such cylinders is illegal in some countries. Fire extinguishers is the easiest way to go but also look at HGV air tanks from commercial vehicle breakers just be wary of any from accident/fire damaged vehicles. I'm currently modifying some old CO2 extinguishers for use as special effects confetti canons they have a test pressure of 200 BAR but they will only be used at 10 BAR or less which I'd say is a pretty good safety margin.

[Sir Cumference]

...... I'm currently modifying some old CO2 extinguishers for use as special effects confetti canons they have a test pressure of 200 BAR but they will only be used at 10 BAR or less which I'd say is a pretty good safety margin.

Interesting!
What kind of valve do you intend use?

[Dark_Lizerd]

Why all the fuss with modifing air bottles for use that is not their intent???

Just so everyone knows...
There are portable air tanks for use to fill car tires and such....
Some even come with their own chargers... and some are even 12v DC powered for use while you are on the road...

So... with that available, why try to modify one yourself...
(Other thn the thrill of modifying something for 'other' uses...)

[Riddle]

Why all the fuss with modifing air bottles for use that is not their intent???

Why all the fuss? Each person's cost/benefit analysis is different. The main factor is cost with what is on- hand or readily available. A 5 kg FE is cheap once used, small, easily moved, and intended for long-term storage of compressed gas.

Some have a 20 gallon or larger compressor, some have FE's available, and some can go buy a portable air tank. As for me, I have purchased 2, 5, and 20 gallon compressors; have owned three different 12 volt tire inflator models; and have owned two different portable air tanks (7 and 11 gallon). Even with a 20 gallon compressor, my 2 gallon sees the most use. The 5 gallon one was given away because its cfm and pressure was not enough enough better than the 2 gal one. With all these available, a smaller tank such as a FE is still of interest to me.

There are portable air tanks...

Have you owned a portable air tank or read the directions for one? The directions specifically state that it is not to be used for anything other than inflating tires. Replacing the inflator hose is also forbidden. After each use, the tank is to be emptied up-side down to remove all water from the tank and stored without pressure. Changing out the hose with an air quick coupler, filling through the quick-coupler, and leaving the tank pressurized all violate manufacturer warnings. Therefore, using such a tank is actually more dangerous than modifying a FE. I am currently looking for an appropriate replacement for my remaining portable tank which is about to expire (the other one already expired).

[mfx]

...... I'm currently modifying some old CO2 extinguishers for use as special effects confetti canons they have a test pressure of 200 BAR but they will only be used at 10 BAR or less which I'd say is a pretty good safety margin.

Interesting!
What kind of valve do you intend use?

Sorry for the delay in replying, I'm making brass adapters to go from the standard M26*1.5 thread on the fire extinguisher (Bought the Die of EBay) to BSP thread so I can stick a standard solenoid valve on it.

[mfx]

Just so everyone knows...
There are portable air tanks for use to fill car tires and such....
Some even come with their own chargers... and some are even 12v DC powered for use while you are on the road...

Not available in all parts of the world, certainly not common in the UK. If you're not familiar with pressure vessel safety and regulations concerning them then they are not something to be messed with lightly but if you know what you are doing then using things like fire extinguishes can be done quite safely particularly if you operate well within their rated pressure. A few key things to do and not do with pressure vessels/systems :-

DO NOT weld/braze your own fittings to pressure vessels/pipework unless you are an extremely experienced (preferably coded) welder with facilities to test the weld and properly pressure test the system.
DO NOT pressure test a newly built system with gas, perform a hydrostatic test (if you don't know what that means you shouldn't be messing with pressure systems).
DO only use properly rated pipework/connectors for the pressures you're working at.
DO fit an overpressure safety valve and a pressure gauge.
DO ensure the system is completely de-pressurised before making any modifications/repairs to it.

Finally a useful tip for the UK any vessel operating at 50BAR/litres (also known as category B vessels) or less (i.e. multiply the receiver volume by the pressure) is exempt from notified body testing/certification but must still be built using sound engineering practice.

[Sir Cumference]

...... I'm currently modifying some old CO2 extinguishers for use as special effects confetti canons they have a test pressure of 200 BAR but they will only be used at 10 BAR or less which I'd say is a pretty good safety margin.

Interesting!
What kind of valve do you intend use?

Sorry for the delay in replying, I'm making brass adapters to go from the standard M26*1.5 thread on the fire extinguisher (Bought the Die of EBay) to BSP thread so I can stick a standard solenoid valve on it.

Ok, thanks.

I have been looking into the pulse valves used for beating dust of filter bags.

They are very interesting..... And correspondingly pricey.

[mfx]

Ok, thanks.

I have been looking into the pulse valves used for beating dust of filter bags.

They are very interesting..... And correspondingly pricey.

I looked at them briefly, basically a pimped up servo (piloted) valve by the looks of them.

[mhw]

I didn't bothered to read whole thread, so sorry if it was stated already, but there's airzound solution out there, which seems to be safe and easy to use solution.
It's loud bicycle horn, made of bottle that holds compressed air, valve button and a horn. Commressed air is pressed into a bottle by bicycle pump, then when you'll press a valve, air goes to horn. Seems idea could be simply adapted with regular PET bottles and some bicycle valves(or maybe even original product could be used) - it gives little amount of pressure(link more bottles?), but it's surely safe and easily reusable.

[Sir Cumference]

Airzound has not been discussed (but it is relatively expensive compared to a practically free powder bottle).

PET bottles have a relatively limited volume and a much lower burst pressure. They will explode violently at approx 8 bar.
(The bang is very impressive, I've done it on purpose). Powder bottles are normally pressurized to 16 bar, and tested to 30, giving you a nice safety margin.
(And you want that, working with compressed gas!)


.... but we basically covered that previously.