Heliax is not light. And we had problems keeping moisture out of the system. Nitrogen under pressure is the best, but often is a maintance issue. (leaks)
I have seen people try to use drying agents on compressed air. Never liked those systems, did not seem to work properly. Air compressors by nature produce water in the compression tank.
At my first station, we had what looked like a cast aluminum tire pump, the kind that has two lugs at its base for you to stand on. It had a rectangular glass-windowed compartment on the side that contained dessiccant.
Our transmitter was on a shelf in the back of the control room, so that’s where we kept it.
It’s possible that someone might actually have used it as a tire pump.