From Frank Fahy
David Stevenson’s contempt for the research done by Eunok Jung on the “valveless pump” is not justified by his explanation of the phenomenon (23 February, p 53).
Static longitudinal displacement of the column of liquid in the rigid tube produces no net change of pressure or volume in the flexible section. Therefore the liquid in the rigid section of the tube does not behave like a metal rod suspended between two springs, as he claims. Its “ends” are linked kinematically and dynamically by the fluid in the flexible section.
The term “phase differences between the frequencies of oscillation” is meaningless—frequencies don’t exhibit phase differences. A linear model of the system (for very small amounts of squeeze) does not exhibit mean flow “start”. Perhaps Stevenson could direct us to the publication in which this non-linear phenomenon is modelled and rigorously explained, thereby supporting his contention of wheel reinvention.
Southampton, Hants
