UPDATE: So the 8mm male quick disconnect to 1/8 NPT female adapter worked! Everything now hooks up to everything else just fine. Unfortunately, there’s a new problem.

I have no idea how the gas valve built into the isi Whip works, but this hookup doesn’t seem capable of pushing any CO2 through it! Everything else works, there’s no leaks, and gas can make it all the way through the hose and out the end. But as soon as I screw it onto the isi’s gas hookup, it can’t get through. There’s a video of an isi disassembly here that shows what the valve looks like inside, but I can’t tell much from it. Clearly this thing is some sort of one-way valve, since gas doesn’t escape when you remove a CO2 cartridge… But what’s so special about a cartridge that my janky hookup doesn’t match?

As far as I can tell, nothing in the mechanism budges when you push on it. I don’t think it’s being mechanically opened by screwing the cartridge in. Is it possible that it just requires the explosive amount of pressure released by a punctured CO2 cartridge before it’ll open? I’ve been feeding it 30 PSI. Some quick googling tells me that 8g cartridges usually release 850 to 1100 PSI. Should I just try cranking up the pressure until something happens? I think the problem then becomes, there’s substantially more than 8g of CO2 in my tank… What happens then?

Now, I’ve since stumbled onto this post about just straight up removing the built-in gas hookup and replacing it with a sanke to ball lock conversion kit. That seems like it might be way better than the approach I’ve been using, and I wish I had seen it earlier!