An Engineer in Wonderland – A neat one-way valve
I was cheering on some friends at the London Marathon, and for the first time paid some attention to those stick-shaped balloons that kids bang together to make a noise – most litter bins had at least one pair in.
They are made of not-particularly-stretchy plastic – polyethylene I think – and are blown up hard enough to make a noise a bit like a drum – a thankfully quiet drum – when you hit them.
The valve is simply some more of the skin material formed into a tube and stuffed inside one end. The only closing force appears to come from internal air pressure.
The tube is probably a special shape – I have didn’t think to cut one up when I had the chance.
What ever their shape, they:
- Use only a tiny amount of material.
- Leak negligibly.
- Offer little inflation resistance.
- Withstand considerable pressure.
I have no idea what the proper name for these balloons are although after much consultation with Mr Google I offer ‘cheering sticks’, and also: powerstix, clapper Balloons, stick balloons and cheering balloons.
Anyone know how the valve works?
Or the name of the valve?
A few days later….
Thanks to the generous donation of a few cheering balloons by the son of a friend, and the intrepid investigations of that friend and her children, we have access to the facts.
Here is the valve from the outside.
There are two flaps of polythene that you blow between – using a straw if you have one – thanks to Steve Kurt’s comment below for adding the straw fact.
Here is the inside of the valve.
It is 46x130mm and made of two plastic sheets welded together.
And here it is in action. As far as the assembled investigating team could see, it is some natural attraction between the two sheets of polythene, probably aided and abetted by moisture, that stops air seeping out of the assembly.
If you can answer this, respond below, or to alice@electronicsweekly.