Hi Luke, I also brew in 40 L batches but I no chill so I ferment in 20 L batches which I usually give about a minute of oxygen, so for a 40 L batch I would give about 2 minutes to get the same level of oxygenation. As for what sort of regulator is best it really doesn't matter because as I said, you will end up just setting flow rate by visual inspection. The trials done by someone (I can't remember who) used 1 LPM flow rate which is where that figure comes from. A typical argon flow meter is setup to indicate for values around 4-8 LPM for TIG welding up to around 18-20 LPM for MIG and up more still for thermal cutting since oxygen has a different density to argon you have to apply a conversion factor of 0.89 (see attached file which gives LPM indicated = lpm o2 * 1.05 /1.18) so the 1 LPM is now 0.89 LPM indicated on the argon flow meter. You can buy special low flow rate oxygen flow meters for not a lot of money but you still have mount them and stuff around with fittings and set them up and put them away again every time etc.
In practice too high a flow rate where the bubbles break the surface like a geyser is just wasteful of gas so you want to get as much gas dissolved into the wort as possible and some filling the head space of your fermenter. Bubbles will accumulate as you do this so give it 2 minutes for 40 L OR until the foam starts to piss out over the top the fermenter, whichever comes first.
As you can see in the home setup it is not an exact science so there is not a lot to be gained with the extra components, but in saying that, there is no harm either.
Regards, Dave
