From David Stevenson
Regarding your article about Eunok Jung’s experiments with the “valveless pump”
(2 February, p 39),
the water in the length of rigid pipe linked with the
flexible section will behave like a metal rod suspended between two springs and
will have its own resonant frequency.
Such oscillations will distort the flexible section and change its cross
section on each side. Phase differences between the frequencies of oscillation
and squeezing explain the flow reversal as the latter speeds up. The researchers
could save money by contacting a consultancy in fluid dynamics rather than
relying on DIY and reinventing the wheel.
Newbury, Berkshire
