The Water Motor
Thomas B. Greenslade, Jr.
Kenyon College, Gambier, Ohio 43022, U.S.A.
This paper deals with devices used to produce motive power as an alternative to small electric motors in the 20th century. The devices illustrated where mainly used for instruction but the physical principals, scaled up, are key to electric power generation today.
At the beginning of the twentieth century, water motors competed, in a small way, with the electric motor for providing rotary motion in the laboratory and shop. Water was cheap, and electricity, when available, was expensive. One hundred years later, the descendants of the water motor are vital components in producing cheap, hydroelectric power.
Down at the Old Mill Stream, the physics of the water wheel, Fig 1, depends on how the water meets the buckets or vanes of the wheel. When the water flows beneath the wheel in the undershot configuration, the kinetic energy of the flowing water is converted into the rotational kinetic energy of the wheel. Water dropping onto the top of the wheel in the overshot
The physicist in me has sympathy with the author of the 1856 Benjamin, Pike, Jr. Catalogue who wrote that “the action of the machine does not, as sometimes stated, depend on the resistance of the atmosphere to the jet from the cross-pipe, but is wholly owing to the hydrostatic pressure of the column of water on the vertical tube.” The ready acceptance of jet and rocket propulsion has not made students any less likely to have trouble with Newton’s third law.
Figure 3 is an example of Hero’s Engine that is listed in the 1900 Leybold catalogue at $6.00; the alcohol burner used to boil the water in the hollow sphere is from the same era. We know nothing biographical about Hero of Alexandria. Even his dates are unknown, but internal evidence suggests that he was writing about 62 A.D. It is not clear if he invented the two devices which bear his name: Hero’s Fountain and Hero’s Engine.
The unusual water mill in Figs 4(a) and 4(b) is at the apparatus collection of Creighton University in Omaha, Nebraska. It has the name of E.S. Ritchie of Boston stenciled on its side and has the green color with gold striping characteristic of metal apparatus made by Ritchie, but I have been unable to locate it in the Ritchie catalogues from the last forty years of the 19th century in my collection. The apparatus shares the funnel and long tube with the Barker’s Mill in Fig. 2, but the mechanism at the bottom, shown in Fig. 4(b), is completely different. Here we see curved turbine blades against which jets of water play.
The true water motor that was used for light-duty power generation in the laboratory and workshop is built on the principle of the Pelton Wheel. The glass side of the motor in Fig. 5 shows that the basic mechanism: a series of concave buckets attached to the rim of a rotating wheel that are struck by the incoming water jet. It is listed at $55.00 in the 1929 catalogue of the Central Scientific Company; the 1941 catalogue lists it at the same price, but by 1950 it was $90.00. The pressure of the water from the city water mains is monitored by the gauge at the top. This apparatus is at the center of a rather elaborate experiment described by Robert A. Millikan in his first book, Mechanics, Molecular Physics and Heat,
dating from 1903 (ref 1). The power output of the motor is measured with a device called a Prony Brake, and compared to the energy per unit time delivered by the water to the motor. Motors of this sort typically put out a fraction of a horsepower.
The water motor in Fig. 6 is rather more utilitarian. A very similar model is described in the 1929 catalogue of the Chicago Apparatus Company at a cost of $6.25: “Water Motor Outfit, Complete: A reliable motor, fully guaranteed, intended for grinding and polishing. Becomes a most efficient bottle and flask washer by simply attaching a wire handle brush to the end of the spindle. From a laboratory standpoint the design is such that efficiency tests can be made to good advantage. Develops one-eighth horsepower with eighty pounds [per square inch] of water pressure. Outfit includes four-inch motor, four-inch beveled face emery wheel; felt buffing wheel and cake of polish for brass, copper and silver; wood pulley grooved for 1/32-inch round belt; and coupling for threaded faucet. Entire outfit is securely packed in neat corrugated box.
Weight about six pounds.” The six inch model, costing $2.00 more, developed one-quarter horsepower. To a first approximation, the power output seems to go as the square of the diameter of the wheel.
The water-powered centrifuge in Fig. 7 has had a rough history. It was rescued, thirty or forty years ago, by an undergraduate from a pile of instruments being thrown away at his institution. Several years ago it was donated to the Greenslade Collection after the now-mature graduate saw an article in the Columbus, Ohio Dispatch about the Collection. It is listed in the 1909 catalogue of the Scientific Materials Company of Pittsburgh, along with a hand-rotated centrifuge
and an electric model. The hand-propelled model cost $10.00, the water-powered one was $12.00 and the electrically-powered one sold for $32.00.
The last example is the small demonstration model of a water-turbine in Fig. 8. The disk in the middle of the glass tube
middle of the glass tube has a series of twelve slots. Water from above is forced through these slots, and the resulting jets of water turn the turbine blades. When connected to a water faucet, the device spins rapidly, and, if a belt were connected to the pulley at the top, it could do useful work. This is an unusual piece of apparatus; I have never seen another one and it does not appear in my collection of apparatus catalogues.
- Robert Andrews Millikan, Mechanics, Molecular Physics and Heat (Ginn and Company, Boston, 1902), pp. 47-50.