Yo Steve
Yes I always found it odd that whilst the vehicles in our EMUs were bolted together with semi-permanent couplings, the air pipes were flexible quick release types with self sealing star valves. However there were MRPICs (Main Res Pipe Isolating Cocks - referred to colloquially as 'Mister Picks') on the end of each vehicle to shut it all off if the hoses burst, and they were self-venting at the hose end.
I've put a piccy of Star Valves below. As you can probably work out, they're the ones pointed to with light blue arrows, and are shown here on the end of unit electrical connector box which I'm sure you're familiar with in concept. The star valves in the Main Res Pipe hoses are very similar.
And you mentioned Wheelslide shenanigans. I don't think about the railway much since I left, EXCEPT for when I get up on a damp autumn morning and remember the apprehension of taking an early morning train out, knowing that I had to be VERRRRRRY careful not to slide through stations when the wheels picked up.
And then when you rolled slowly into a station some **** would lean out in front of you and tap his watch.
Every time someone did that I knocked 10 mph off my already slow speed.
Hah. Take care, John