Example - telescoping tubes

A secondary problem concerning candidate #5 of the above can-raising example is how/where to source the telescoping tubes suitable for a fluid pressure which cannot exceed 100 kPa for safety reasons?

An all too common approach here is to visit the nearest hardware shop on the lookout for plastic or light alloy tubes of different diameters and thicknesses which may nest inside one another - and on being unable to unearth suitable tubes, to trash the candidate as impracticable. This lack of effort is deplorable. What one might do is . . . .

A simple p = F/A demonstrates that a pressure of 100 kPa acting over a circular area of only 11 mm dia will support a mass of 1 kg. Alternatively, if the whole 0.16 m² plan area of the device is available to lift the can then the necessary fluid pressure is a paltry 60 Pa (6 mm H₂O). These limits indicate that intermediate pressures and areas could be used successfully, and that metal tubes are not necessary to withstand the operating pressure. So, recalling that the environment is dry ambient, we further practicalise by asking what other materials/manufacture might be used?

• We might glue cardboard or paper or plastic, winding up tubes helically like the support tubes for toilet rolls eg., using the next smaller tube as a mandrel. Each tube might consist of multiple layers of differing hand, built up on a temporary innermost layer which is later removed to ensure clearance between adjacent tubes. Depending on the material, the thickness of each tube could be easily adjusted to withstand the internal pressure.

• A very light tissue paper tube could be close wound with nylon fishing line - the former component when impregnated with Araldite eg. ensures a leakproof tube, the latter provides reinforcement to withstand the bursting effect of the internal pressure. This idea might be criticised because of the difficulty of a leakproof sliding seal outside the tube due to the corrugations formed by the fishing line. But further practicalisation might reveal that the interstices could be filled with smoothed setting plastic - or they might be put to good use as a reservoir for a honey-like substance doing double duty as a speed retarder and a fluid seal (due to its surface tension and viscosity).

• Composite tubes could be formed in the same manner as Saturn fuel tanks, by winding reinforcing fibres helically around a mandrel (possibly using a lathe for uniform pitch) then impregnating/spraying them with a solidifying plastic. Subsequent machining for a smooth external surface might be necessary.

• Tubes could be centrifugally cast by quickly rotating a tubular mould into which a setting plastic eg. is poured. Centrifugal force causes the liquid to form a uniform film which sets inside the mould. A tube so formed could become the mould for the next smaller tube.

• Tubes might be made from rubber hose, allowing radial expansion to prevent air leakage.

• The large radial gap between adjacent sizes of tube available in the shops - which led to the proposed scrapping of the telescoping tube idea - might be put to good use as a mould cavity in which to cast an intermediate tube. There are many casting plastics and latex rubbers available on the market. The fishing line reinforcement mentioned above might be incorporated again here.

And so on. The foregoing doesn't pretend to be an exhaustive list of ideas, and the tertiary problems have not yet all been resolved - ie. telescoping tubes have not yet been fully practicalised. But we now have sufficient confidence to persevere with the underlying idea and to justify further research and development - ie. experimentation - which could lead to full practicalisation.
In no way can trashing be justified !

Note how practicalisation here is just another mini- problem solving exercise.