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Figure 14-11 Siphon System Flow Calculation without Siphon Influence Determine flow capacity of siphon system if siphon is broken so flow is only by gravity and assumed head. Siphon is comprised of two 4-inch diameter pipes that convey water from inside of the Northwest Intake portal to a manhole located outby the sealed Northwest Intake. These two pipes are each approximately 225 feet long. They both flow into a 6-inch diameter pipe located in the manhole. The 6-inch diameter pipe conveys flow to Outtall 002. Flow through a pipe is determined by the amount of head causing flow and the head loss in the pipe resisting flow. Flow rates are calculated by trial and error by varying the flow rate so the assumed or actual head causing flow equals or exceeds the head loss in the pipe. Experience is used to assure the slow rate is reasonable for the pipe size. Available Head 2 Feet Allows for minor pool behind NW Intake Seal Max Flow with 2 toot of head -One 4-inch oioe 100 gpm Pipe Diameter -PVC 4 inches Inside Diameter 4 inches Area 0.087 SF Velocity 2.55 fUsec Pipe Length From Mine To Manhole outside 225 Feet Three sweep elbows - 7-feet each 21 Feet • Total 246 Feet Loss in oioe Plastic Pipe C= 130 Entrance loss k(v^2)/2g 0.08 Feet Friction loss in pipe = f f = 0.2083(100/C)^1.85 ' q^1.85/d^4.8655 0.76 Feet per 100 Feet Total Loss in pipe 1.94 Feet 246 Feet 6-Inch PVC Pipe from Manhole to Discharge Design Flow -from two 4-inch pipes 200 gpm Pipe Diameter -PVC 6 inches Inside Diameter 6 inches Pipe Length Manhole to 90 degree bend 280 Under Interstate 70 270 Through meter to discharge 30 Two 90 degree bend equivalent length - 16 ea 32 612 Loss in pipe Plastic Pipe C= 130 Friction loss in pipe = f f = 0.2083(100/C)^1.85 ' q^1.85/d^4.8655 0.38 Feet per 100 Feet 2.32 Feet 612 Feet Conclusion: Each 4-inch pipe will carry approximately 100 gpm with no siphon influence. • The six inch pipe has sufficient slope (head causing flow) to overcome 2.32 feet of head loss. Therefore the siphon piping system will handle 200 gpm with no siphon influence. 01 /01