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Sewer Problem 1 - Determine pipe flow capacity and required pipe size:
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Find the capacity of an existing 18" concrete storm sewer pipe having a 1% slope at full flow. What size concrete sewer pipe should it be replaced with to carry 18 cfs? What size pipe would be required if it were to be replaced with PVC? |
1. From the sewer menu open the flow (Q) calculation for a round pipe, RndPipeQ.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables.
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2.
For the mannings roughness coefficient open up the coefficient table and look up the correct manning's coefficient.
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3. Put in the manning's coefficient and click on the "Calculate" button. Review the results. The capacity of the 18" concrete sewer pipe is 9.099 cfs.
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4.
To determine the required concrete pipe diameter for 18 cfs, open up the pipe diameter calculation, RndPipeD.aspx. Input the "Title", "Designer/Checker" and variable information.
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5.
After inputting the variables, click on the "Calculate" button. Review the results. Use a 24" concrete pipe to carry 18 cfs.
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6.
To determine the required size for PVC pipe, open the coefficients table. Look up the manning's roughness coefficient for PVC.
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7.
Enter the manning's roughness coefficient for PVC and click the "Calculate" button. Review the results. Use a 20" PVC pipe.
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8. Summary
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The existing 18" concrete sewer pipe has a capacity of 9.1 cfs. To carry 18 cfs would require a 24" diameter concrete sewer pipe. If PVC pipe is used the pipe diameter can be reduced to 20".
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