VERTICAL SECTION OF DRINKING-STRAW REGULATOR

Moshe F Rubinstein, Patterns of Problem Solving, Prentice-Hall, 1975

The drinking-straw regulator [at right], designed to enforce a uniform rate of drinking from a wine barrel, has its origin in China of the 12th century A.D.. The bamboo tube is about two feet long and has in it a float with cone-shaped ends. When the straw is not in use, the float sinks, closing the opening. When a drinker sucks from the top, the float rises. If he sucks too rapidaly, it makes the top opening smaller; if he sucks too slowly, the lower opening gets smaller.... The control scheme is not fully automatic because the equilibrium state of flow is achieved by the drinker who optimizes the sucking rate.