Valve for venting Helium

[Ekashman Tiwari]

Hi everyone! 

I am new to the group, and we (team members are all beginners in the field) are planning to do a weather balloon project in which we aim to maximise the ceiling of the balloon without allowing it to burst, by venting some helium at a stage, enough so that it later reaches the floater condition, and further venting it to make a controlled descent to the ground. For this, the main problem which arises is of the valve. 

As I can figure out from the available information (including from this group), people design the valve themselves (because the commercial ones are heavy and low temperature intolerable). It would be great if the members here help me by providing some details of the valve you have used for a similar objective. Criticisms/improvements for the project objective are also welcome. 

Thanks and regards,

Ekashman Tiwari

[Mika Köching]

Hi!

Great you're interested in high altitude ballooning!

Here's some criticism from my side: Doing this is extrememly difficult. I'm working on it for a few months now and haven't even got a valve yet that is suitable. You have to be able to go wide open to let out quite a lot of gas. Another problem is controlling the release. You have to get it exactly right. This is difficult to do because GPS data isn't that accurate.

If you only want it to go as high as possible, I wouldn't use a valve. I think you'd be better off just taking out the valve and thus minimizing wheight.

Especially because you are still new to this, start with something small and simple. I personally prefer two small launches over one big. If you start with a complex payload and big balloon and you make an error (which you most certainly will) and you lose the payload, it's a big loss.

I think development and experiments in this area are very important, but I also think this isn't suitable as a beginner project.

Hope that helped.

73s from Mika, DL8MIK

[Steve]

I think your team have already been in contact? - but at the risk of repeating things here is the valve I made and flew:-

    https://www.youtube.com/watch?v=eahxgo7u5nI

basically its a RC servo that lifts a disk with a silicone rubber seal (part of a glup style drinks bottle).  The disk seals due to the  balloon pressure and the spring.

There are 6 vent holes at the bottom - positioned equally around the base - to null out any thrust from the escaping gas. If I remember correctly I applied some heating to ensure the servo did not freeze.

You won't be able to float a balloon at its maximum altitude - if you release enough gas to arrest ascent it will float some way below its burst altitude.

My experience is that it is very difficult to release exactly the right amount of gas to float - too much and it slowly descends, too little and it continues to rise.

 I think the groups that have successful done this have used a combination of a valve and ballast drop.

    Steve

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[Ekashman Tiwari]

To Mika: Thanks for the advice, I shall surely consider it.

To Steve: Yes, sorry, actually I had approached through IRC first, but there was some issue so I could never see the replies which might have come.
Thanks a lot for detailing about your design. I had seen that video, and really wanted to know how it worked, so your reply comes as a very valuable resource. We will now attempt to recreate it through CAD, and I wonder if I can approach you later if there arise some issues. Actually we are required to do something different with ballooning, so I had thought of this idea. It doesn't quite matter that we will not be able to attain float, what is important is to carry out an interesting technological demonstration. 

Another thing that I want to ask: What do people usually do for launch if they are based in an unfavourable terrain or near the sea - do they travel everytime miles to find a suitable site, or do they robustly rely on the radio communications so that they do not have to worry about the payload recovery? We are at the southernmost part of India, and the trajectory simulation very clearly shows the payload going into the sea!

Ekash