The idea is credited to a Scottish inventor called Robert Stirling in 1816. The idea is that a fixed quantity of air is pushed between two chambers one hot and one cold. The resulting changes in air temperature and pressure can then be used to perform work.I have seen this little pump in many forms In the late sixty's I saw one on a television science program one made entirely of glass with ball bearings for the valves and heat from a from a spotlight to power the device. Another I have seen was made from metal piping and heat supplied from a lit gas jet to power the device.
The one in the illustration can be made from cheap plastic irrigation water piping fittings and values from a cheap plastic hand liquid pump.
The one thing common to all models is that all joints be air tight.
The items you will need
as in illustration or to make it a little easier you could use small irrigation or garden water fittings that come with threaded ends.
It is then just a case of screwing them together.
The flat valves could be pieces out of the liquid pump
Two three or two litre empty plastic coke bottles with their tops .These will be the air chambers one for hot one for cold
Construction
The alignment is of as in the illustration. The illustration is pretty clear I believe and just to add to it, the following information may be of assistance to you
Remove the tops from the coke bottles and drill a quarter inch hole in center of each top
Cement with plastic putty or whatever you have available the tops in one side of a T Piece make sure that it cannot move and is air tight . You will need two of these , and when the unit is finished the plastic bottle will be screw into the glued plastic tops.
Connect other pieces as in diagram. You may use what ever you can for valves but they should be light round and flat or even a glass marble fitted into a rounded drill hole in flat piece of plastic inserted or glued into a irrigation connection piece and most important they must only allow water to flow in one direction and block it from flowing backwards
The other type of valve could be the same drilled hole but with a piece of flat rounded plastic resting on top of it placed on such a way that it cannot move sideways but can move freely upwards and downward.
Priming the pump
Place suction inlet into source of water and pour water into top of unit until level with second level piece under the plastic bottle tops. Water should now be flowing out of the outlet pipe when correct level is reached
Place plastic bottles in position ,one bottle should be exposed to sunlight and the other kept as cool as possible.
Improvements that could be worth trying are
Put some black paint inside a plastic bottle and roll around until the inside surface is covered with the black paint. This will be the bottle exposed to the solar heat.
The other could have a large tin can collar with a small hole in bottom of the can to allow the thread of plastic bottle to exit and be joined to rest of connections. This should have a water tight seal to prevent leakage. When properly sealed, add water to collar and natural evaportion will keep thre plastic bootle cooled.
Or alternately use more connections so that the bottles could be stood right way up and the cooling bottle put into can from the top.
How it works:
The invention alternatively pulls up water through the bottom value and then pushes it through the top valve.
When the air heats up in the hot air bottle pressure expands thus forcing the water in tube out . When the air is cooled down it contracts creating a vaccum that pulls water up through the bottom and so on.
The unit should keep working until heat source is removed. You may need to experiment to make this unit work more efficiently.
Possible use
Although this is only a demo unit a bigger one could be built and used in a hydroponic garden for water cycling or for the cooling unit in the solar desalination unit described elsewhere.
