A critical part of launching a high altitude balloon is obviously getting the helium out of the tank and into the balloon. It is possible to hold the balloon directly on the nozzle of the helium tank. However, they are not designed for this and will likely lead to a frustrating launch. The preferred method to fill the balloon is to make a hose to connect the helium tank and the balloon. The one problem with this is that you won’t have access to the helium tank until you rent one the day of the launch.
Fortunately, Team Space Balloon posted a great article (the site no longer exists) that details the types of fittings needed and how to create a very simple helium filling hose. The helium tanks found at party supply stores require a CGA-580 nozzle. Most tubing found at your local home improvement store will follow NPT standards. So you need an adapter. I was able to find a CGA-580 to NPT 1/2″ adapter at airgas.com (part # RAD64003976). Then I took this part to Home Depot and bought some 1/2″ braided tubing and a matching pipe clamp. Assembly took about 30 seconds.
The next issue to resolve is how to measure the balloon lift while the balloon is being filled. This can be accomplished very easily by attaching a loop of heavy-duty string to the balloon end of the hose. This loop of string will allow a hanging scale to be hooked on to measure balloon lift. I used a Dremel to cut a small groove around the tube near the balloon end. Then I tied some kite string around the groove and covered it with plenty of duct tape to hold it in place. When it’s time to fill the balloon, the balloon should be lightly duct taped to the filling hose and held by someone at all times to prevent the balloon from taking off on its own. Then just attach the hanging scale to measure how much lift you have.
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