Creating airtight seals

[Amy Li]

Hi UKHAS,

I'm currently working with the Imperial College Space Society on a HAB that uses an AI algorithm to change altitude to stay geostationary. Our current altitude control mechanism is an archimedes screw to dispense ballast and a solenoid valve to vent lift gas. However, we need to design an adaptor to connect the balloon opening (larger) to the tubing that connects to the solenoid valve (smaller). We're currently thinking of using caulk to create an airtight seal between the adaptor and the tubing. If anyone with experience in airtight seals could provide an advice on whether this would work or if there is a better way, we'd really appreciate that!

Best,

Amy

[Steve]

Couple of cable ties around some pvc tube should be good enough as:

    1) its not at a lot of pressure while on the ground.

    2) when at altitude the pressure is a bit higher but the volume is much larger too (gas molecules greater dispersed - take longer to escape).

It took several minutes for enough gas to escape through a 1in diameter opening to arrest ascent.

I do recommend a groove in the tube as the neck cable tied to PVC tube can slip:- a la: 

    https://ukhas.org.uk/lib/exe/fetch.php?cache=&w=640&h=480&tok=c5cfe8&media=guides:filler1.jpg

    Steve

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[Nick McCloud]

On Friday, 6 June 2025 at 23:08:26 UTC+1 Amy Li wrote:

 solenoid valve

If you route it inside the payload box which is reasonably well taped, it should stay warm enough - outside it gets to -40degC on the way up .... 

[Amy Li]

Hi Steve,

Thanks for your advice again :)

I was moreso wondering how you connected the hose in your image to the white valve. Did you use an adhesive or clamp?

Best,
Amy

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[Steve]

For the avoidance of doubt , the item in this photo:

    https://ukhas.org.uk/lib/exe/fetch.php?cache=&w=640&h=480&tok=c5cfe8&media=guides:filler1.jpg

is a fill tube (for filling the balloon) not the valve - its just that the construction is similar as the valve and uses the same grove idea to ensure the balloon neck wont slip off.

There are some more pictures of the fill tube here:

    https://ukhas.org.uk/doku.php?id=guides:fill_tube

The outer tube, internal spacer and clear braided hose are all PVC of different kinds. They glue very well with superglue (cyanoacrylate adhesive).  The spacer is made from several layers of (lightweight) foamed PVC and turned to a close fit with the outer tube glued in place .

Here is a similar Idea - where I made a container that fits within the balloon neck that held the electronics (the parachute was inside the balloon):

    https://www.flickr.com/photos/16828840@N07/albums/72157631341732946/

The tube is slightly larger than the balloon neck diameter (as was the valve) so the neck stretches over the tube - then it is held in place with cable ties over the groves.  There is no clamp or adhesive just cable ties and the fact the neck is a tight fit over the tube.

Hope that helps.

    Steve G8KHW

To view this discussion visit https://groups.google.com/d/msgid/ukhas/CAMYRYRRymLroc%2BwDL9dkSdk78cF5fXrz4rubpcz_YAY3hmi%2BSw%40mail.gmail.com.

[Nick McCloud]

On Wednesday, 11 June 2025 at 21:25:02 UTC+1 Steve wrote:

Here is a similar Idea - where I made a container that fits within the balloon neck that held the electronics (the parachute was inside the balloon):

    https://www.flickr.com/photos/16828840@N07/albums/72157631341732946/

What balloon type / size is that? Looking at how transparent it is, I presume that it must of burst in to a gazillion pieces so no impediment to the parachute?

Which, to save on a supplementary question, is that a home made parachute? How do you scale them down or is it best guess?

 

[Steve]

It was a 100g balloon probably a Pawan.  Similar sized neck to the Hwoyee (much bigger than ToTex 100g).

Used a standard model rocketry parachute - 12in parasheet I think  (no need for balloon attachment as its not inline with the balloon).

I launched a few of these - all appeared to deploy the parachute correctly.   I would think that even if the balloon didn't shred the hole would be big enough for the parachute would work its way out at some stage during the descent.

    Steve G8KHW

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