I've heard of JD techs using regulated air pressure to check the old scv valves.
My take is that it's a procedure used to check the integrity of a valve overhaul...make sure the valve is adjusted properly and that the seats, poppets, balls, tornado springs, etc are all good...
At the dealership I used to work at..we had a manual hyd. pump looking deal(like bottle jack pump) that we were supposed to use to pressure test the valves after overhaul. I never used it much although I tried to a couple times....same principal as using pressure regulated air.
I always put all new goodies(guides needles poppets balls springs)...also used a brass punch and hammer to beat in the new poppet into the fresh ground seat of those old poppet valves and carefully adjusted them...never had much issue unless the valve body itself was defective..cracked or had a seat that wouldn't grind