WATER WHEELS AND TURBINES 497 
_ 6. Ina series of brake tests of a small Pelton wheel the following tabulated 
results were obtained :— 
65 | 67 | 54 | 47 44 | 35 2°9 2°1 10 | 00 
960 | 1360 | 1480 | 1800 | 1900 | 2240 | 2520 | 2800 | 3280 | 3580 
where W=effective load in lbs. on brake lever at 12 inches from axis of wheel, 
and N=speed of wheel in revolutions ye minute. The weight of water used 
in each test was 41°5 lbs. per minute, and the pressure of the water was 700 lbs. 
_ per square inch in the pipe behind the orifice. The diameter of the orifice was 
835 inch. Complete the above table by adding the brake horse-power and 
the efficiency per cent. Plot the brake horse-power and efficiency on a speed 
ase. Scales.—Horse-power, 2 inches to 1 horse-power; efficiency, 1 inch to 
20 cent. ; speed, 1 inch to 500 revolutions per minute. State the maximum 
eke biorse. power and the maximum efficiency. 
: 7. Show that the efficiency of a Pelton wheel is a maximum, neglecting 
frictional and other losses, when the velocity of the cups equals half the velocity 
of the jet. 25 cubic feet of water are supplied per second to a Pelton wheel 
thro a nozzle, the area of which is 44 square inches, The velocity of the 
_ cups is 41 feet per second. Determine the horse-power of the wheel, taking a 
reasonable value for the efficiency. [Inst.C.E.] 
8. A Pelton wheel is to run at 900 revolutions per minute. The head of 
water is 720 feet, and the maximum water supply is 15 cubic feet per minute. 
Determine the diameter of the wheel, the diameter of the nozzle, and the 
maximum power developed, assuming an over-all efficiency of 0°8. [U.L.] 
q 9. Explain why it may happen that when the opening through the nozzle of 
a Pelton wheel has a certain area the power of the wheel may be diminished by 
agg and also by decreasing the opening. 
10. The following particulars relate to a Girard impulse wheel. Using the 
notation of Art. 426, p. 490, 0,=19°, $,=36°, ¢.=15°, 7,=4 feet, r2=4°6 
feet. Total head=500 Feet, Absolute velocity of water at entrance = 85 per 
cent, of theoretical velocity due to total head. Volume of water entering wheel 
a second=8 cubic feet. Determine the velocities 1, ¢,, ¢g, %, Ug, and vy in 
feet per second, also the angle @,, the speed in revolutions per minute, and 
_ the horse-power of the wheel, neglecting losses in the wheel itself. 
: 11. In a Girard impulse wheel, using the notation of Art. 426, p. 490, 
— 0,=20°, ¢,=40°, g.=15°, r,=2 feet, r==2°5 feet, 1,=80 feet per second, and 
_ water passing through wheel per second =25 cubic feet. Determine the velocities 
C1, Co, Uy, Ug, aNd vy in feet per second, also the angle @,, the speed in revolutions 
th gaa and the horse-power of the wheel, neglecting losses in the wheel 
tse . 
12. A simple reaction wheel of the Barker’s mill type is supplied with water 
_ at a head of 10 feet. The combined areas of the orifices amount to 40 square 
_ inches, and the velocity of the centres of the orifices is 24 feet per second. 
_ Find the horse-power if the net efficiency is 60 per cent,, and find also the 
hydraulic efficiency. [U.L.] 
18. Certain experiments with a jet reaction wheel showed thai the maximum 
efficiency was obtained when c= ,/2gh (using the notation of Art, 427, p. 
491). Taking the coefficient of velocity for the orifices as 0°95, calculate the 
maximum efficiency and the percentage of the energy due to the head h which 
is carried away by the water leaving the wheel. 
14. A parallel flow impulse turbine works under a head of 64 feet. The 
_ water is discharged from the wheel in an axial direction with a velocity due to ~ 
a head of 4 feet. The circumferential speed of the wheel at its mean diameter 
_ is 40 feet per second. Neglecting all frictional losses, determine the mean vane 
_ and guide angles. [U.L.] 
s 15. The rim of an inward flow turbine moves at a speed of 30 feet per second, 
_ and the vanes are there at right angles tothe rim. Water enters the rim with 
a radial velocity of 5 feet per second. If the water is to enter without shock, 
what must be the angle between the rim and the guide blades? Find the 
weight of water entering per second if the circumferential area of all the open- 
_ ings of the rim is 2°4 square feet. [B.E.]} 
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