B.9 - CHART 8 and CHART 9

A.

Square Manhole on Through Pipeline at Junction of a 90° Lateral Pipe - Charts 8 & 9 (Larger Size Laterals: D _L / D _O > 0.6)

Pressure change coefficients for use in determining the elevation of the pressure line of the 90° lateral pipe are obtained from Figure B.8 Chart 8, and the coefficients for the upstream in-line pipe are obtained from Figure B.9 Chart 9. The diameter of the lateral pipe must be at least 0.6 of the diameter of the outfall pipe to permit use of these charts. Pressure changes at junctions of smaller laterals may be obtained through use of Figure B.10 Chart 10. The coefficients given by the charts 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. The design of manholes with deflector devices is discussed separately.

To use the charts:

1.

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

2.

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

3.

Calculate the ratios Q _U /Q _O , D _U /D _O , and D _L /D _O . If D _L /D _O is less than 0.6, use Figure B.10 Chart 10 instead of Figure B.8 Chart 8 and Figure B.9 Chart 9.

4.

Calculate the ratio B/D _O and note if the outfall entrance is rounded.

5.

Calculate the factor  ; if this is greater than 1.00, use Figure B.10 Chart 10 instead of Figure B.8 Chart 8 and Figure B.9 Chart 9.

For lateral pipe:

6.

Enter the lower graph of Figure B.8 Chart 8 at the ratio D _L /D _O and read  at the curve or interpolated curve for the ratio B/D _O .

7.

For a rounded outfall pipe entrance or one formed by a pipe socket as defined by Gen. Instr. 6, reduce the chart value of  by 0.2.

8.

Determine the factor ML by entering the upper graph of Figure B.8 Chart 8 at the value of the factor  and at the curve or interpolated curve for D _L /D _O .

9.

Calculate  .

10.

Calculate the lateral pipe pressure change

11.

Add h _L to the elevation of the outfall pipe pressure line at the branch point to obtain the elevation of the lateral pipe pressure line at this point.

For upstream in-line pipe:

12.

Enter the lower graph of Figure B.9 Chart 9 at the ratio D _L /D _O and read  at the curve or interpolated curve for B/D _O .

13.

For a rounded entrance to the outfall pipe or one formed by a pipe socket, reduce by 0.2.

14.

Determine the factor MU from the upper graph of Figure B.9 Chart 9.

15.

Calculate K _U = M _U x .

16.

Calculate the upstream in-line pipe pressure change: 

17.

Add h _U to 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.

For water surface:

18.

The water-surface elevation in the manhole will correspond to the upstream in-line pipe pressure line at the branch point.

19.

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.

B.

Round Manhole on Through Pipeline At Junction of a 90° Lateral Pipe-Charts 8 and 9 (Larger Size Laterals: D _L /D _O > 0.6)

Pressure change coefficients may also be obtained from Figure B.8 Chart 8 and Figure B.9 Chart 9 for use in determining the elevations of the pressure lines of the 90° lateral pipe and the upstream in-line pipe connected by a round manhole to an outfall pipe.

To use the charts:

1.

Proceed as instructed by steps (1) through (6) for a square manhole at a similar junction to obtain a base value of  .

For lateral pipe:

2.

To provide for the effects of the round manhole cross-section, reduce  in accordance with the following table:

Reduction of 

The reduced values apply for a sharp-edged entrance to the outfall pipe.

3.

With a well-rounded entrance to the outfall pipe from a round manhole, reduce  obtained in step (2) by 0.1.

4.

Determine the factor ML from the upper graph of Figure B.8 Chart 8 and proceed as instructed in steps (8) through (11) for a square manhole to complete the determination of the elevation of the lateral pipe pressure line.

For upstream in-line pipe:

5.

Proceed as instructed in steps (12) through (17) for a square manhole at a similar junction to obtain the elevation of the upstream in-line pipe pressure line. Note that no reduction of is to be made for effects of the round manhole cross-section.

For water surface:

6.

Proceed as instructed by steps (18) and (19) for a square manhole at a similar junction.

C.

Deflectors in Square or Round Manholes on Through Pipeline at Junction of a 90° Lateral Pipe-Charts 8 and 9 (Larger Size Laterals: D _L /D _O > 0.6)

Pressure change coefficients are also presented in Figure B.8 Chart 8 and Figure B.9 Chart 9 for use in determining the elevations of the pressure lines of the lateral and in-line pipes at a junction of this type, with either a square or a round manhole modified by flow deflectors. Deflectors in a manhole effectively eliminate the effects related to the shape of the manhole. Deflector types are described in the instructions for use of Figure B.8 Chart 8 for a manhole with deflectors at a 90° deflection of a storm drain. The curved and 45° deflectors cannot be used in a manhole on a through pipeline because of the space required for through in-line flow.

To use the charts:

1.

Proceed as instructed in steps (1) through (9) for deflectors in a manhole at a 90° deflection, disregarding references to 45° or curved walls. Through use of Figure B.8 Chart 8 these steps will give the elevation of the lateral pipe pressure line at the branch point. As noted in the instructions for a manhole of this type without deflectors, Figure B.10 Chart 10 must be used when D _L /D _O > 0.6 or  > 1.00.

For upstream in-line pipe:

2.

Enter the lower graph of Figure B.9 Chart 9 at the ratio D _L /D _O and read  for all manhole sizes and any deflector wall angle from 0° to 15° at the curve for B/D _O = 1.00.

3.

For a rounded entrance to the outfall pipe or one formed by a pipe socket, reduce  by 0.1.

4.

Determine the factor M _U from the upper graph of Figure B.9 Chart 9.

5.

Calculate K _U = M _U x  .

6.

Calculate the upstream in-line pipe pressure change h _U = K _U   .

7.

Add h _U to 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.

For water surface:

8.

The water-surface elevation in the manhole will correspond to the upstream in-line pipe pressure line at the branch point.

9.

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.9 Chart 9 - Square Or Round Manhole On Through Pipeline At Junction Of A 90° Lateral Pipe (In-line Pipe Coefficient) (Source University of Missouri E.S.B. #41)