The fill tube is the mechanism constructed mainly out of PVC pipe that aids in the filling of the balloon and connects the balloon to the flight string. It is not commercially available, but can be assembled using easily accessible pieces. It is highly recommended that glue and/or other substances are used to render the entire mechanism airtight and stable. This fill tube is suitable for the Hwoyee balloons which have the large, 8.3 cm neck size. It will not work with the Kaymont variety, which have much smaller necks.


The Fill Tube is constructed out of 8 parts, which each have a specific job in ensuring the success of the device. Each part is listed in order of size.

The 3" Drain Pipe to Schedule 40 AdapterEdit

This adapter is to connect 3" drainpipe to 3" schedule 40 PVC. The adapter is the piece that the neck of the balloon stretches over and grips onto. The reason that an adapter is used is because the ridge in the middle (See above) provides an excellent place for the neck of the balloon to hold to. This, in combination with the O ring (see below), ensures that the balloon is secured tight enough that it will not slip off of the Fill Tube.

The 3" Drain Pipe (lightweight, not schedule 40)Edit

This piece connects the 3"-3 1/2" adapter to the 3" cap.

The 3" Drain Pipe CapEdit

This is the part of the Fill Tube that the Helium hose screws into. The hole will need to be drilled manually, and threads for the hose/cap to screw into glued in. The cap is glued onto the adapter to form the main body of the Fill Tube.

The O-ring (Size 336 BUNA O-Ring)Edit

The 2 7/8" inside diameter, by 3 1/4" outside diameter by 3/16" width O-ring ensures that the balloon will not slip off of the adapter by holding the neck of the balloon tight against the lip of the adapter, creating friction that makes it almost impossible for the balloon to slip off.

Threaded Tube/Nipple
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Fill tube with the neck of a balloon that has already been used


This piece secures the 3/4" to the Fill tube to seal up the hole that the Helium Tube screws into. One end is screwed into the 3/4" cap, through the 1" plain to 3/4" threaded pipe reducer, which is glued onto the inside of the cap, and the other end screws into the Fill Tube. It is recommended that you wrap Teflon Tape around the tube to ensure that the seal is airtight and will not let any Helium escape the balloon.

The 1" Plain to 3/4" Threaded Pipe ReducerEdit

This piece is glued to the inside of the 3" drain pipe cap so that the threaded tube/nipple has something to screw into.

The 3/4" CapEdit

This piece covers the hole where the Helium tube fixes into the Fill Tube. The cap has an eye-bolt threaded into it to which you attach the flight string. During filling, the cap is off and the threaded tube/nipple is attached to the Helium tank fill hose. After filling, the fill hose is removed from the threaded tube/nipple and the cap (with flight string attached) is screwed on.


The two metal eye-bolts have different purposes. The one on the 3/4" cap is used to tie the flight string to the Fill Tube, and the second one, on the 3" cap, is used to anchor the balloon while it is being filled with Helium and can also be used to test the lift of the balloon by tying a string to a set of weights equal to the desired lift of the balloon, and filling the balloon until the balloon lifts the weights into equilibrium.

Using the Fill TubeEdit

The neck of the balloon is stretched over the adapter to about halfway down the device.

The rubber O-ring is then placed over the neck of the balloon right at the base of the lip created by the 3" drain pipe to schedule 40 adapter.

The lip and the rubber O-ring create enough friction necessary to hold the balloon on securely, without glue or zipties.

The opening on the other end is where the helium then fills into the balloon.

Once the sufficient amount of helium is in the balloon, the hose is removed and the opening is replaced by the 3/4" cap.

The flight string is tied to the eye-bolt on the cap and the packages are then in turn tied to the flight string.

The second eye-bolt is to anchor the balloon while it is filling and to attach weights while filling to ensure the proper lift is achieved.

You will want to make sure that the whole device is airtight so no helium will escape because that can be the most expensive and vital part of the whole project.