Computing Slope of
Pipe
Horizontal runs of sewer and drain pipe
must slope to permit flow and prevent
blockage. Computing the total amount of slope
for a horizontal run of pipe permits the
builder’s level to be used to accurately position
the run of pipe, Figure 4-25.
Metric Measurement
Some industries have adopted the metric
system of measurement. Since many construc-
tion trades, such as plumbing, are not involved
in international commerce, there is less pres-
sure for them to change. However, some
fixtures, faucets, and valves are now available
in metric sizes.
The base unit of length measurement in the
metric system is shown in Figure 4-26, along
with comparable U.S. customary units. One of
the chief advantages of using the metric system
is the ease of changing from one metric unit to
another simply by multiplying or dividing by
multiples of 10. This is easier than using the
various conversion factors required in the
conventional inch-pound system.
Unlike U.S. customary measure, where
dimensions are often expressed in both feet
96
Section 1 Introduction to Plumbing
Figure 4-22. Determining the volume of a rectang-
ular tank.
6′
12′
4′
Volume = Length (L) × Width (W) × Height (H)
This formula is frequently written
V = LWH
Substituting the dimensions from the above drawing
V = 12′ × 4′ × 6′
V = 288 cubic feet
Figure 4-23. Determining the volume of a cylindri-
cal tank.
6′
2′
Volume = PI × Radius squared × Height
This formula may be written:
V = πr2h
Substituting from the above drawing:
V = 3.14 × (2′)2 × 6′
V = 75.36 cubic feet
Figure 4-24. Converting cubic inches and cubic feet to gallons.
To Convert To Procedure Example
Cubic inches Gallons Divide by 231 376 cu. in. = 376 ÷ 231 = 1.63 gal.
Cubic feet Gallons Multiply by 7.48 6 cu. ft. = 6 × 7.48 = 44.88 gal.
Generally, horizontal pipe runs in sewers
and drains are required to slope 1¼8″ to 1¼4″
per foot of run.
Code Note