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# inflaTUBE

tyres that auto-inflate as you ride
 (+19) [vote for, against]

the tubes in bicycle tyres leak air slowly; replenish tyre pressure on the go with inflaTUBE.

This is a small plastic reciprocating pump that can be put right inside the tube, with just a few millimetres of travel and maybe a cubic centimetre or so of capacity. the pump is squeezed and released when it reaches the lowest point in the course of rotation of the wheel.

the travel of the pump would be close to, but slightly greater than, the expected distortion of the tube at its lowest point when properly inflated.

the ideal place for this would be underneath the actual valve (through which you normally pump in air), but using many inflatubes at different radial positions may also be useful for greater pumping capacity.

 — arvin, Aug 25 2006

Diagram http://aravindet.go...s.com/inflatube.gif
a pretty detailed diagram [arvin, Aug 25 2006]

Wow, great description and diagram. (+)
 — jellydoughnut, Aug 25 2006

A beautiful way to avoid patching your tire. I love it.
 — jmvw, Aug 26 2006

 this is a lovely idea, however I'm a bit concerned that the wheel would wobble like hell because of the imbalance in weight, and also if you went over a bump at the 'wrong' bit of the tyre you'd feel the full force (or the piston would burst through the outer tube).

it might just work though (+).
 — neilp, Aug 26 2006

In that third diagram of yours (bottom right), why would atmospheric air be drawn in if there was still enough pressure inside the tire to push the piston down? Wouldn't the piston have to be pulled down from an outside force to create enough of a vacuum to draw in more air? Or maybe this function would stop working when tire pressure got too high, and only work in a slightly deflated tire, acting as and overinflation capping device.
 — jellydoughnut, Aug 26 2006

Yes, that bothered me too, [jellydoughnut]. But the piston is joined to the tyre (right?) so air pressure in the tyre could indeed cause the piston to expand, drawing in outside air as described (+).
 — spidermother, Aug 26 2006

 yes, [spidermother]... the piston and cylinder are attached (glued?) to opposite points inside the tube. the force needed to draw the piston out is pretty small - it only needs to overcome friction and the viscosity-induced pressure drop across an open valve; the tube pressure would be more than sufficient for this.

 overinflation as [jd] says will not occur because once the tire is properly inflated, the "flattening out" will be small, and therefore piston travel will be too small to pump more air. the idea of a rubber bladder is good (eases manufacturing) as long as it is about the same size - the pump's cross section should be small as compared to the tire's contact patch, otherwise there would be a significant difference in pressure and "bump" every time that part of the tire touches the ground.

 the bladder would also eliminate [neilp]'s concern, which is a pretty serious one especially if the tire is underinflated. i had initially thought of making the cylinder flexible so that if the required travel is greater than design limits, the cylinder would bend momentarily. the bladder idea seems more attractive though.

oh and thanks for all the comments. and buns :)
 — arvin, Aug 26 2006

arvin, the piston need not be solid. It could be a small rubber bag, which is flexible enough to take all the bumps etc. I'm thinking of a whoopee type bag, with an extra valve.
The only problem is that there would be a strange sound. All explanations regarding the source of the sound would be met with much scorn, I think.
 — Ling, Aug 28 2006

 I'm very, very impressed by the diagram [+]

The idea was ok too...
 — Mr Phase, Aug 28 2006

 ling and arvin : the piston has to be rigid to allow a difference in air pressure between the inside of the tire and the inside of the piston. I think the bladder idea doesn't work..

 spidermother : having a very light spring in the piston , or filling the piston with open-bubbles foam .. could solve the problem of expanding the piston when the tire is flat ?

 The overinflation problem seems easy to solve.

cute idea !
 — shitwolk, Jul 01 2008

Great idea! Though I'm a little worried that the pump could be broken if you hit a hard bump.
 — MisterQED, Jul 02 2008

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