so you would set the guage to 15lpm?
Yes, exactly. Maybe a bit more (17Lpm?) if I were using a larger tank, just to be certain the CO2 is adequately removed, but 15Lpm is the recommended minimum flow and will make a 20cf cylinder last the recommended ~40 min to be certain of ctb.
A regulator typically has two guages: a pressure gauge, telling you how much gas you have in the cylinder, and a flowmeter, that tells you the rate at which the gas is flowing out of the cylinder. The pressure gauge is almost irrelevant for our purposes, since we'll be starting with a fully-charged small cylinder and letting it go completely empty over the process of ctb. The flowmeter is the important gauge, for what we need.
When purchasing a regulator, you want to make sure the flowmeter is marked in Lpm. If the gauge reads in Cfm only, it might not allow a heavy enough flow; that's very common, since 15Lpm is a very heavy flow for some welders and so not all the regulators allow it. If the regulator's flowmeter only reads in Cfm (it'll say on the dial face), look at how high the flowmeter goes, do the math to convert Cfm to Lpm, and make certain the regulator will do what you need.
Is this the same type of regulator you guys have:
Pretty much. There are a lot of variants out there, but this one is pretty basic.
Sorry for stupid question, but does"reductor"/"reducer" and "regulator" the same device ? I am a real potato at all this technical stuff, so I appreciate if somebody will make it clear for me.
I haven't heard a regulator referred to as a "reductor"/"reducer" --BUT, since the purpose of the device is to reduce the cylinder pressure to a useable and steady flow, I can see how the term "reducer" could be used.
Gas cylinders operate at very high pressures --far too high to simply run a hose off of one and into your exit bag or mask. What's more, the cylinder pressure changes/drops as the amount of gas inside the cylinder drops. All a regulator does is control the release of gas from the cylinder: it reduces the pressure to a useable level and releases the gas in a controlled, steady flow.