High Pressure Systems - Gases |
| Acetylene (Maroon
tank, left-hand thread) is available from welding supply shops. It is not
really suitable due to it's ease of combustibility. Not recommended.
Air (Grey tank, right hand thread) is available from diving schools and BOC, but is normally supplied heavily compressed (3-4000 psi) and as such is a bit of a nightmare to transfer to other containers safely. Can be generated onboard using a compressor (such as a tyre inflator) but the flow rate from even petrol driven compressors is pretty low. Argon (Blue tank, right-hand thread, can cause asphyxiation) can be used. It is used for welding certain metals and can be obtained easily, but it can be more expensive. Certainly other Noble gases are in the costly category. Check out the information on the BOC pages to find out more about their properties. At high concentration, will sufficate without warning. Carbon Dioxide (CO2 ) (Black or Black with white strip tank, right-hand thread, causes asphyxiation) is stored as a liquid when compressed beyond about 40bar. As the liquid is exposed to less pressure (through a regulator) so it vents and releases the gas. This gives a constant gas supply. The downside of this is that it can cause potential problems if the liquid should accidentally drain through a regulator and then suddenly expand in the lower pressure environment. You will almost certainly blow a seal or two at best. It could be dangerous too. Stories of cylinders exploding are not exagerations. On the plus side though CO2 can be exhausted into the body of the robot to help cooling of course!! And it puts out fires! I did also find that CO2 is not stocked as readily these days as there is not much demand for it. Ring before you go to a supplier. CO2 is also widely used by the paintball community. It's worth talking to these guys as they have decanters, regulators, cylinders and all sorts available cheap and ready to go. They will also explain things like decanting - which is a dangerous process and frowned on by the likes of BOC and Air Products - and connections. Helium (Brown with beige shoulders tank, inert but can cause asphyxiation at high concentration) is the gas used for kiddies ballons. Aside from the well known side-effect that it makes your voice go higher when inhaled, it also liquifies at low temperatures. It is quite expensive (about 2-3 times the cost of carbon dioxide) and tends to be available in smaller containers. Also, the ballon gas supplied by BOC and others is in fact not pure helium but a mixture with air. The air diffuses out the helium, so they don't keep well - this is also why ballons tend to fall to the floor after a few days! Hydrogen (Red tank, left-hand thread, non-toxic, very volatile) is the gas used in the airships of the early 20th centuary. Highly explosive and dangerous. Do not use. Nitrogen (Grey and black tank, right-hand thread, non-toxic but can cause asphyxiation) is cheap, plentiful and pretty harmless. It also puts out fires quite well and can be got from a supplier like BOC pretty cheaply. (By the way, BOC supply you with a cylinder once you have opened an account with them - anyone can do so. You then 'rent' the cylinder for the year and just pay for the gas you use over that. The cylinder was about 30UKP for the year, but if you don't use it for a whole year, you get a partial refund.) The problem for a fire extinguisher is that it uses different connectors to CO2 so you would have to come up with your own way of decanting from the supply to your tank. Nitrogen makes up about 78% of the atmosphere and is a common side product of oxygen production. Oxygen (Black tank, right-hand thread, non-toxic) is not really a good idea. Pure oxygen tends to encourage fires in a hot environment and that reason alone should make you wary. Air is good if you can get it supplied at high pressure. Diving schools can refill cylinders for minimum cost, but again you need to make a connector to the holding cylinder. Diving cylinders are too high pressure to use directly, by the way, and they tend to be very heavy to cope with such high pressure. Shame, would be the easy way otherwise! Propane (Red tank,
left-hand thread, has added fish-like smell) is not usable. This is the
gas used for burners and portable fires. It is very volatile and burns
readily. Do not use.
Cylinder Identification: Labels state the following information.
|