Since a theoretical horsepower is only 75 per cent efficient, he would require 10 × 4/3 = 13.33 theoretical horsepower of water, in this instance. Substituting the values of the problem in the formula, we have:
What capacity of wheel would this prospect (400 cubic feet of water a minute falling 17.6 feet, and developing 13.33 horsepower) require?
By referring to the table of velocities, we find that the velocity for 17.5 feet head (nearly) is 33.6 feet a second. Four hundred feet of water a minute is 400/60 = 6.67 cu. ft. a second. Substituting these values, in formula (B) then, we have:
Quantity of Water
Let us take still another problem which the prospector may be called on to solve: A man finds that he can conveniently get a fall of 27 feet. He desires 20 actual horsepower. What quantity of water will be necessary, and what capacity wheel?
Twenty actual horsepower will be 20 × 4/3 = 26.67 theoretical horsepower. Formula:
