Im so confused by what gas to get. They seem to be advertised per L but I was told that THIS 60L of gas wouldn't last me any time but then THIS 20L of gas is more expensive? How do I know what I'm getting? I assume the fill weight would tell me but that doesn't seem to be listed anywhere?
The 60L is misleading, that's probably how much space the gas would occupy if it wasn't compressed. The volume of the cylinder is 0.95L
so many noughts is makes no sense. the smaller bottle is 60l of gas compressed to how ever many bar typically we weld at around 10l of gas per minute so lasts around 6min. the bigger bottle is a 20l bottle at a pressure to I am guessing 150/200 bar. so say 200 x20l = maybe 4000l I remember being baffled by this and worked out the price per litre of gas at (STP say around 14psi) I have a dim memory of either 1000x the volume of gas or 10000 times the volume of gas for about 5x the price
The item showing is a disposable bottle, And won't last more than a few minutes, 20Ltr refillable bottles hold much more gas at a higher pressure, A BOC 20Ltr bottle at 230bar pressure will last around five or six hours of weldingL
the 60ltr will last about 5 minutes if your lucky its 60ltr at atmospheric pressure. a rent free 20ltr from say SGS will be at 200 bar. so at atmospheric would give you 4000ltr as stated above. BOC are normally 230. hobby welf bottles are either 135 bar or 300 bar. just use the formula PxV/T = a constant. as the gas flow is so low temperature becomes near enough irrelevant.
4000l of gas divided by around 8L per min gives about 50 hours of welding. I usually run mine around 8LPM, but whatever size and pressure they always run out on a Friday afternoon when you are in creative constructive mode.
We are talking about 2 different capacities here. The disposable cartridge is 60L of gas, whereas the refillable cylinder has a water capacity of 9L, you then times this by the pressure to get the gas capacity ie 9L x 137bar = 1233L of gas. This was always straight forward for me - there again I used to scuba dive, so was always able to work this out as I had to know my consumption rate, to ensure I planned a safe dive.
On normal welding bottles they are given a capacity in litres. A 10 litre bottle will hold 10 litres of gas with no compression which is equal to 1 bar or atmospheric pressure. To get another 1 bar of pressure you have to push another 10 litres of gas in there so as said above to work out how many "free air" litres of gas are in there you just multiply the capacity by the pressure. Ie, 10 litres X 130 bar = 1300 litres. The regulator you attach holds back the pressure and only lets some of the gas out at a time. You can choose how fast the gas comes out but a rough guide for mig would be at the rate of 8 litres per minute. So if you know you have 1300l of gas you can divide that by 8 to give you 162 minutes of welding time. The little disposable bottles have such a pathetic amount of gas in them that they would never be able to sell them for £20 if they told you that you would only get 4mins of welding so they use the other figure of the "free air" amount to make it seem like a good idea. You can tell from the amount of members telling you not to buy one that it's a waste of money to buy those! Co2 is a little different to the other welding gasses. When you start compressing co2 it turns in to a liquid at a relatively low pressure. You can not compress a liquid so once it has got to the liquid stage it is sold by how much of this liquid is in the bottle and the easiest way to tell how much is in there is to fill them by weight. Again, a little disposable bottle may contain 500g of liquid cow if you are lucky. A proper bottle will contain 10kg and only cost £5 more.