Autodesk 235B1-05A761-1301 - AutoCAD MEP 2010 User Manual page 524

The following information outlines how the plumbing line diameter is calculated:
The plumbing module calculates the pressure available for friction loss throughout the supply system
by subtracting Pressure at Source from Pressure of the Highest Fixture, minus Pressure Drop, minus
Friction Loss-Water Meter.
If the available pressure drop is insufficient, then the plumbing module increases the size of all the
components in the run by one size (all sizes go up one plumbing line size) and recalculates Pressure Drop.
If the Restrict Velocity option is enabled and the calculated actual flow velocity exceeds the restricted
velocity, then the plumbing module increases the size of the run by one plumbing line size and recalculates
Pressure Drop.
Once the plumbing module has found the correct plumbing line size, the corresponding standard nominal
size is found from the calculated standard inside diameter. To view the size iterations used by the plumbing
module, see the Standard Plumbing Line Sizing table in the following section.
Standard Plumbing Line Sizing Table
Use the following table as a reference for standard sizing calculations of plumbing lines. All values of d, the
inside diameter of the pipe (plumbing line), are in inches and are based on a Schedule 40 Steel Pipe gauge.
To size the plumbing line, the calculation rounds up to the nearest standard size. The plumbing module
assumes that all plumbing lines being sized are similar to Schedule 40 Standard Steel Pipe when determining
an inside diameter.
If the nominal size is...
0.125
0.25
0.375
0.5
0.75
1
1.25
1.5
2
2.5
3
3.5
4
5
6
506 | Chapter 10 Drawing Plumbing Systems
then the inner diameter is...
0.269
0.364
0.493
0.622
0.824
1.049
1.380
1.610
2.067
2.469
3.068
3.548
4.026
5.047
6.065