(3) **Venturi flume design formula.**

in which

Q = flow through grit chamber of flume discharge;

e

= permissible divergence from design velocity (fps);

r

= ratio of minimum rate of flow to maximum rate of flow; and other symbols are as previously

stated or as indicated in figure C--1**c**.

is 1.67 cfs, that the maximum rate of flow and as high as practicable over the entire range of flows. Assume

a depth in the effluent channel of 1.5 feet at maximum rate of flow. Then the required width (w) would be

5 (1.5 2) = 1 ft. 8 in. The designs for various types of control sections and grit chamber cross-sections

are as follows:

(1) **Proportional weir**. As the depth (h) in the chamber above the weir crest cannot exceed 2 feet

without submerging the crown of the inlet sewer, let h = 1.75 for first trial. Determine W by substitution in

equation C-1. Then,

To prevent appreciable divergence of the velocity from 1 fps when the flows are low, the depth (d) of the

rectangular section of the weir opening should be minimum practicable. As indicated by equations C-2 and

C-3, this depth is a function of b and x. The breadth (b) is limited by the width of the effluent channel (in this

case, 1 ft. 8 in.) and x is limited by the size of solids to be passed (in this case, about 3 inches, assuming that

a bar screen will be ahead of the grit chamber). Try d 0.15 and solve for b in equation 2. Then,

therefore, b = 1.53 (satisfactory). For various values of y, values of y/d are determined and the corresponding

values of x/b are taken from the table; the values of x are then determined as follows:

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