Yes, the automatic flushers are infrared. An infrared LED aims outward.
When a person is in place, some of the IR is reflected back to the valve
area where it is detected. When the person leaves, the reflected light goes
away and the valve is triggered to flush. The electronic circuit is
essentially looking for a change in the IR light received by an IR
photo-detector, and in particular it is looking for a drop in signal. So
when the person walks up, it sees a rise in IR (which it ignores); and when
the person leaves it sees a drop in IR (which triggers the flush).
Many automatic door openers now work this way, except they trigger on the IR
rise rather than the IR fall.
Yes, the battery that operates the IR LED, IR sensor, and circuitry could
never last long if it provided the energy to operate the valve. But valves
that use their own water pressure to help themselves turn on/off have been
around a long time. It involves a diaphragm with relatively large area that
is connected to the actual water valve. Water can be admitted or released
from one side of the diaphragm with a very small valve that does not involve
much energy, and the diaphragm effectively uses its large area to generate
sufficient force to open/close the main valve. This type of actuator is
already present in flush valves that operate manually, and also in the
valves that refill the tank of a conventional toilet. This mechanism also
is present in natural gas valves that control burners on our furnaces and
boilers. This mechanism is also present in the automatic shutoff valves
used to fill our cars with gasoline. It's also present in regulators on
compressed gas cylinders.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817