The secret workings of a transparent pop-pop engine

摘要

The water pulse (Pop-Pop, Putt-Putt or Toe-Toe) engine is an exciting and fascinating device. Even when not made from flexible transparent material, you will be kept watching and wondering for hours at its lively antics. Up to now, the explosive internal operating 'life' cycle could only be heard. Now the enhanced throbbing becomes something you can feel and see. Everyone with an interest in things mechanical cannot but appreciate the sheer audacity of such action achieved without moving parts. Although they have been made for toy boats for over a century (Ref. 1), only some aspects of the way they work have been suggested at various times. What follows summarises the ideas and findings of others and presents some new observations and conclusions from simple experiments with transparent engines. The upper flexible metal plate of an essentially flat boiler was replaced with a piece of overhead projector (OHP) film to permit observation of what was happening inside. The processes in one of the two copper pipes were also observed by replacing it with a silicone rubber tube. A modern video camera system was used to film the action inside the boiler in slow motion. Finally, because OHP film can work up to 250deg. C and is so readily available, some ideas are given for making a transparent engine (fig 1). From 1916 to 1926, McHugh made some very important contributions in two patents (Ref. 2). In the second one, he seems to have clearly and correctly understood the way the oscillatory momentum of the water columns causes the pressure fluctuations in the boiler and how steam condensation onto the walls of the cold tube causes the drop in pressure necessary for pulsation to be initiated and maintained.