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Sizing up a Water Wheel

Sizing up a Water Wheel

The Diameter of a Water Wheel in Relationship to the Number of Arms
Chart applies to both wooden, metal and hybrid water wheels

Diameter in feet- Number of Arms-

3 or less....................4
4 to 8.........................6
10 to 12....................8
14 to 20....................10
16 to 24....................12
20 to 30....................14
24 to 36....................16
32 to 45.....................18
36 and larger............suspension water wheel

A drawing from John Reynold's book "Windmills & Watermills" (1970).

Figure 332- Breast and Overshot (water) Wheels.
Practical Milling, by Prof. B.W. Dedrick,
National Miller, chicago, Illinois 1924.

Overshot or Breast Shot Water Wheels Chart

from
"The American Miller & Millwrights' Assistant"
by William Carter Hughes
Detroit, Harsha and Hart, 1850 first edition

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The following table shows the required length of over shot or breast wheels, on falls from 10 to 30 feet, to drive from one to four run of four and a half feet stones, with all the necessary machinery for a merchant flouring mill. The column marked "Fall" shows the number of feet fall on the breast wheel, or the diameter of the over shot.
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(first column of numbers below: 10,' 11,' 12,' 13.' etc.)
diameter of------Number of run of stones.
waterwheel
in feet----------- 1--2--3--4 -Multiply the number of run required by the length as stated in the table.
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(second column below 7,' 6 1/4,' 5 3/4,' 5 1/2,' etc.)
-----width of------------------Then multiply twice-3 times-4 times (the number of run of millstones)
-----waterwheel
-----in feet
10' 7'
11' 6 1/4'
12' 5 3/4'
13' 5 1/2'
14' 5'
15' 4 1/2'
16' 4 1/4'
17' 4'
18' 4'
19' 3 3/4'
20' 3 1/2'
21' 3 1/4'
22' 3 1/4'
23' 3'
24' 3'
25' 2 3/4'
26' 2 2/3'
27' 2 1/2'
28' 2 1/2'
29' 2 1/2'
30' 2 1/4'
---------------------------------------------------------------------------------------------------------------------Example: What should the length of either a breast or an overshot wheel be, in drive 3 run of stones, on a fall of 18 feet? Look at 18 feet, the height of the head; then we have opposite 4 feet for 4 run, which, multiplied by 3, produces 12 feet, the length required.

A 42 to 46 inch diameter millstone would take about 3,000 gallons per minute to operate and a 56 inch millstone would take about 5,000 gallons per minute to operate. Add up the millstones and add some extra for additional machinery (about 3,000 gallons per minute for the rest of a 4 story building full of machinery). The required horse power per millstone is about 4.5 horse power. This is worked out by using the grinding surface area.

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