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Tests of Water Wheels
By Paul Arr
OF WATER AT ALMOST ZERO VELOCITY. The shape of the jet is maintained until impact in center of bucket, where the entire energy is removed from the water by the bucket, result
ing in maximum efficiency.
TUDYING the action of water on principle to the observation of a water
water wheels at a recent special wheel in actual operation. This principle u demonstration in San Francisco, may be described as being the reverse of
has resulted in modifying several the kinetoscope, in that moving objects · long-established hydraulic theories. It is are seen as stationary instead of in appar.shown that most of these supposed hy- ent motion. The general principle is that draulic laws were mere empiricisms reduced from observations of water action against stationary surfaces; or, if moving, the path of the water was so obscured by spray and the moving wheel that the observations led to mistaken theories, which were disproved by actual demonstration.
The demonstrations which were made with Pelton water wheels showed that the correct method of solving the prob
Fig. 2. TANGENTIAL WATER WHEEL, SHOWING DISCHARGE lems was to observe the action of water on moving surfaces as though they were standing quite still. This is accomplished by applying the stroboscopic
if. a moving object be illuminated at fixed intervals by rays of light admitted at the moment the object passes a desired position, each portion of the object will be observed as though it were stationary. Thus is secured a clear view of what occurs in the cups or buckets of the water wheel while it is in operation under normal conditions.
As an exponent of this principle, there was exhibited the apparatus shown in Fig. 3, consisting of a wheel 20 inches in diameter, mounted on the shaft overhang of a General Electric generator. The water impinges on the wheel through a needle nozzle, the pressure being supplied by a centrifugal pump. The luminant is a General Electric searchlight projector with automatic focal-point control, which is located beneath the apparatus, and which, by a system of mirrors, throws its rays into the wheel housing through the glass bottom. In its normal position the light is thrown directly on splendid results; but the fallacy lay in the fact that most of the hydraulic laws were deduced from observations of water action against stationary surfaces.
the wheel, which may be seen revolving Fig. 1. A 4,000-H. P. TANGENTIAL WATER WHEEL. and the water discharging from the buck
The recent tests thoroughly demonstrated that one of the fundamental principles of hydraulics, as applied to impulse wheels, is that the water must "enter without shock and leave without velocity.” The nearer the approach to this condition, the higher the resultant efficiency. Experiments with the buckets showed that in order to obtain a complete reversal of the stream, with practical absence of velocity, it is essential that the bucket be divided into two parts by a wedge or splitter on which the stream may strike (Fig. 1). In the recent demonstrations, the stream of water was thus divided, the two halves following the curvature of the bucket and discharging backward and downward at a slight angle.
The unique method of observation Fig. 3. GENERAL View of STROBOSCOPIC APPARATUS.
here described, demonstrated that an im
pulse water wheel, in order to attain the ets in apparent confusion. Interposed highest bucket efficiency, must meet the between the searchlight and the wheel is following conditions: a sheet-iron disc with radial slots, which is revolved by means of gearing at a 1. The front wheel of the bucket, in enterspeed proportional to that of the wheel; ing the stream of water, should produce absoand when the searchlight is automatically
lutely no disturbance.
2. The water velocity should be taken up on brought into its upper position, the light the surface of the bucket in a line vertically is thrown on the wheel through these re- under the shaft center, when the bucket surface volving slots. The wheel is thus illumi is in the most advantageous position. nated at fixed intervals, as explained pre
3. 'The water should discharge from the
sides of the buckets without interference with viously; and the onlooker sees it appar
appar- the succeeding buckets or the wheel center, ently standing still, and can observe the and with a minimum velocity of discharge. action of the water, as well as trace the path of the jet, from its entering the bucket to its reversal and clearance of the succeeding buckets.
In designing the waterwheel bucket and attempting to carry out a particular theory, it is necessary to lay out the bucket shape mathematically, and then, following established hydraulic laws regarding the flow of water on surfaces, note the curves and paths which the stream should follow. This plan—the only one heretofore known-has been productive of some
Fig. 5. STREAM OF WATER FROM NEEDLE NOZZLE,
5. No twist or disturbance should occur in the water jet, in order that the greatest possible amount of power may be developed from the moving water (Fig. 4).
The demonstrations showed that the regulation of any water wheel is necessarily at the expense of efficiency. In most cases it is accomplished by throttling the water by means of a gate, which materially reduces the working pressure. The needle nozzle (Fig. 5) is a device which accomplishes the desired result with the least loss in pressure and velocity, and is consequently highly efficient. It consists of a conical shaped tip in which is inserted a concentric tapered plug or needle, generally similar in shape to a “plumb-bob.” A change of position of this plug causes a corresponding change of discharge area in the nozzle. The amount of water used is thus varied, and the power of the wheel proportionately influenced.
Fig. 4. STROBOSCOPIC VIEW OF WATER Wheel Run-
energy is removed from the water.
4. The water should not be carried around with the wheel, and the discharge should occur as soon as the water has transferred its energy to the rotating wheel.
Trains Lighted by Turbines
By F. Peterson
HE accompanying illus- continuous current at 125 volts. The
tration shows a 15-kilo- turbines are supplied with steam at from watt Curtis steam tur- 80 to 200 pounds' pressure, the exhaust bine and electrical gener- passing into the atmosphere, no condensator, mounted on top of ers being employed.
a locomotive in service on The steam-turbine train-lighting unit, the Pennsylvania Railroad. This small as shown, occupies but small space, the direct-connected unit is utilized for train area being 22 inches by 66 inches. In lighting, and its combination of small order to protect the same from the size with relatively large output is possi- weather, sheet-iron casings surrounding ble because of the high speed of the little both the turbine and the generator are prime mover.
provided, which not only reduce the conThis equipment includes an 80-volt di- densation losses, but protect the generrect-current electrical generator of the ator and turbine from moisture and dirt. two-pole type, driven at a speed of 4,000 The exhaust is carried into the stack revolutions per minute by a Curtis steam when the train-lighting set is mounted turbine constructed at Schenectady, N. on the locomotive; and when mounted in Y., by the General Electric Company. the 'baggage car, the steam is obtained The entire turbine and generator weigh from the locomotive by a flexible steam only 1,850 pounds, and supply current hose and coupling. not only for general train lighting, but The separate steam dynamo unit is also for the operation of the locomotive more generally favored for electric trainheadlight.
lighting, not only on account of its simThese train-lighting sets are also con- plicity of operation and electrical connecstructed of 20-kilowatt and 25-kilowatt tions, but also on account of its reliabilcapacity, operating at a speed of 3,600 ity. Electrical generators driven by the revolutions per minute, and supplying axles of the cars are in satisfactory operation both in this country and in Europe; also charging the storage cells. A small but storage batteries are absolutely es- coil is in series with the lamps, which is sential; and, in fact, with any system of energized as soon as the load is switched train lighting, even with the separate on, and its effect is to render the field steam-turbine generator, the accumulator excitation more positive, though it is not plant is essential.
absolutely required. The Leitner-Lucas train-lighting sys Another automatic device employed is tem utilizes automatic regulating and used for switching in the battery when switching devices in connection with the the train comes to a stop. With the syselectrical generators, lamps, and storage tem using a separate dynamo driven from batteries, when starting the voltage be- the car axle in connection with the stortween the positive and negative terminals age battery, each railway coach has its of the battery excites the field of the elec- own independent plant, including dytrical generator, assisting the current namo, battery, and switchboard, with aufrom the main brushes, the field building tomatic regulating apparatus. up rapidly. The current from the arma With the turbo-generator outfit on the ture increases; and the current instead of locomotive shown in the accompanying being supplied from the storage battery illustration the entire electrical equipas the automatic switches come into ac- ment is compact and of light weight, and tion, is obtained from the electrical gen- compares favorably in economy as well as erator, not only lighting the lamps, but reliability.
What Ancient Cannon Were Like
By Dr. Alfred Gradenwitz
Berlin Correspondent, Technical World Magazine
catapults, in construction so mys- the works of the military writers of both
many centuries, have finally been models of the ancient weapons. His crereproduced. For this, credit is due Lieu- ations have partly been donated to natenant Schramm of the German Army. tional museums; the remainder have been
sent to the Kaiser, for Saalburg Castle.
Greek ordnance—which was adopted by the Romans without any material alteration—was, almost without exception, dependent on the hand-bow principle. On trying to shoot a larger bullet to greater distances, the elastic arms of the bow were necessarily made so strong as to be no longer susceptible of tightening by hand. A tension shaft had there
fore to be fitted to the bow, which shaft · was tightened with levers or hand
wheels. Finally, as the power of bows altogether failed to ensure the efficiency desired, their bending elasticity was replaced by the tensional elasticity of neura,
that is, ropes made from animal ANCIENT GREEK HAND-Bow.
sinews, woman's hair, or, in an emerCalled a "Gastraphetes,” tension being obtained by gency, horsehair. One of the accompressing the body against curved back end
panying illustrations represents three