TM 5-814-2/AFM 88-11, Vol. 2
Source:
Design and Construction of Sanitary and Storm Sewers WPCF Manual of Practice No. 9
by Water Pollution Control Federation, 1970, p. 83.
Figure 5-1. Chart for Hazen-Williams formula.
(2) Velocity. Velocity criteria for force mains
to warrant a minimum velocity of 3.5 fps with one pump
are based on the fact that suspended organic solids do
operating, the design may call for both pumps to be
not settle out at a velocity of 2.0 foot per second or
operated manually once a week for a sufficient period of
greater. Solids will settle at velocities less than 1.0 fps
time to flush out the line. Larger stations having three
and when wastewater pumps are idle. However, a
or more pumping units, which operate a major portion of
velocity of 2.5 to 3.5 fps is generally adequate to
the time, will require minimum force main velocities
resuspend and flush the solids from the line. Force
ranging from 2.0 fps with one pump operating, to 5.0 fps
mains serving small pump stations, which are designed
with several pumps operating. In these cases, it is only
to operate on an intermittant basis, will be sized to
required
provide a minimum velocity of 3.5 fps at the peak
discharge rate. For small stations having flows too low
5-2
Previous Page
