Sedimentation Drain Design
Drain Sizing
The time it takes to drain the sed tank can be approximated by:
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\large
$$
desiredT = {{16W_
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^
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\tan (AN_
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)^
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L_
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} \over {3\pi D_
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^2 \sqrt
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}} + {{\sqrt {HW_
} - \sqrt {{{W_
} \over 2}\tan (AN_
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)} } \over {{{\pi D_
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^2 } \over {8L_
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W_
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}}\sqrt {{
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\over {Pi_
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}}} }}
$$
where WSedBay is the width of a single sedimentation bay, ANSedPlate is the angle of the bottom slopes from the horizontal, LSed is the length of the sedimentation tank, DValve is the diameter of the drain valve, HWSed is the water height in the sedimentation tank, and PiVenaContractaOrifice is the head loss through the valve.
A function to determine the valve diameter iterates from the smallest possible diameter to the largest diameter, calculating the respective drain times using the time function. The valve diameter function returns the smallest diameter that allows the sedimentation tank to drain within the time defined by the user. The iteration stops once the calculated diameter drains the sedimentation tank at least as fast as the desired time.
Couplings
The calculated nominal diameter is that of the slip side of the adapter and is used to calculate its inner and outer diameters. The outer diameter of the slip side is also the inner diameter of the threaded side. The outer diameter of the threaded side is used as the inner diameter of the valve which fits it.
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Drain Slopes
Since the center of the valve is aligned with the floor of the sedimentation tank, slopes are required in the floor of the tank. The slopes have a width equal to the diameter of the valve and a depth equal to half the diameter (placing the center of the valve at-grade) with a slope of 30 degrees.
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Gate Valves
Gate valves are placed in every bay of every sedimentation tank at-grade to allow for draining.
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