European train travellers may soon be thanking Hitachi of Japan. The
company’s engineering division has filed a European patent application (593
163) on a system which avoids the unpleasant ear-popping that affects passengers
when a high-speed train enters a tunnel. This is caused by the piston action
of the train,which upsets the pressure balance of the air entering the air-conditioning
fans at the ends of the coaches.
The solution, according to Hitachi, is so simple that it is surprising
that it has not been thought up before. A sensor on the train registers
any significant change in pressure, and separately switches the frequency
of the power supply for the air inlet and outlet fans, up or down, to compensate.
