I have found an appropriate source for helium. After a bit of searching, I found a balloon wholesaler, All American Balloons, right here in Arlington, usually catering to large parties and car dealerships. The shop is well equipped to rent out a 125 cu. ft. tank for about $60, and they have been most helpful by allowing me to look at the tank to make sure I have proper fittings.
Getting the helium out of the tank and into the balloon has taken more planning than I would have thought. I could plan on using a standard balloon valve that comes on rentals from the party store, but that's a pretty small seal when compared to the 2-3 inch neck of the sounding balloon. Instead, I have assembled an adapter that fits the 5/8" valve on the tank, and expands to a 3" collar. The balloon neck fits easily without much extra space. Cost: $13
I'm almost there. I just need to sort out the phone, and we're ready to launch!
