I honestly thought he was going to do more than welding, though welding improve the seal and maximum pressure goes way up, meaning you can generate loads more power. Still I did think he was going to go and make an electric generator/motor. He can produce enough juice to make some magnets, copper wire seems easy enough, they could probably make graphite cause brushless would be too hard. He could also teach them about hydraulic presses which is another pre ww2 technology which put teh germans on the production map. Stamp out entire parts in 1 solid piece. Lighter, stronger and there is a higher level of accuracy and precision. Teach them about gearing, screws, chucks, then horizontal/vertical mills and lathes. Show them planetary gear sets, then teh n+1 and n gear set up for major reductions. It would be fun, up until machine logic, programming and computers.