B.10 - CHART 10 - Square or Round Manhole on Through Pipe Line at Junction of 90° Lateral Pipe (Smaller Size Laterals D / D < 0.6)

Pressure change coefficients are presented in Figure B.10 Chart 10 for use in determining the common elevation of the pressure lines of the lateral and in-line pipes at a junction of this type for cases of pipe sizes or flow divisions outside the range over which Figure B.8 Chart 8 and Figure B.9 Chart 9 may be applied. Figure B.8 Chart 8 and Figure B.9 Chart 9 are more reliable within their range and should be used if possible. Neither manhole shape nor size nor relative size of lateral pipe modify the coefficients of Figure B.10 Chart 10. The chart may also be used for direct connection of a 90° lateral to a main without use of a manhole. The coefficients of the chart apply directly to a square-edged entrance to the outfall pipe. Coefficients for a rounded entrance are obtained by reduction of the chart values as stated below. Deflectors in the manhole are not effective in the ranges covered by Figure B.10 Chart 10, and therefore need not be used.

To use the chart:

1.

Determine the outfall pipe pressure line elevation - Gen. Instr. 1.

2.

Calculate the velocity head in the outfall - Gen. Instr. 2.

3.

Calculate the ratios D _L /D _O , D _U /D _O , and Q _U /Q _O - Note that use of Figure B.8 Chart 8 and Figure B.9 Chart 9 is advisable if the size and flow factors are within their range. Figure B.10 Chart 10 should not be used for Q _U /Q _O < 0.7 if other solutions are possible.

4.

Note whether the outfall entrance is to be rounded or formed by a pipe socket as defined by Gen. Instr. 6.

5.

Enter Figure B.10 Chart 10 at the ratio D _U /D _O and read K _U (also equal to K _L ) at the curve or interpolated curve for Q _U /Q _O .

6.

6. If  was found to be greater than 1.00 in an attempt to use Figure B.8 Chart 8 and Figure B.9 Chart 9, K _U of step (5) will be negative in sign, thus providing a check on proper use of the charts.

7.

For rounded entrance from the manhole to the outfall pipe use the reduced values from the chart.

8.

Calculate the change-of pressure h _U = h _L = K _U   , h _U and h _L are positive or negative depending on the sign of K _U as read from the chart.

9.

Add a positive h _U to or subtract a negative h _U from the elevation of the outfall pipe pressure line at the branch point to obtain the elevation of the upstream in-line pipe pressure line at this point.

10.

The elevation of the lateral pipe pressure line at the branch point and the water surface elevation in the manhole will correspond to the upstream in-line pipe pressure line elevation found in step (9).

11.

Check to be sure that the water-surface elevation is above the pipe crowns to justify using these charts and that it is sufficiently below the top of the manhole to indicate safety from overflow.

Figure B.10 Chart 10 - Square Or Round Manhole On Through Pipeline At Junction Of A 90° Lateral Pipe (For Conditions Outside Range Of Figure B.8 Chart 8 and Figure B.9 Chart 9) (Source University of Missouri E.S.B. #41)