Figure 1-7. Prevention of cross connection in acid or cinder fill.
(1) Requirement. Pumping is necessary if the slope of the wastewater line
does not produce required minimum velocity or where wastewater must be lifted to a
higher elevation. Wastewater can be pumped through pressure lines (force mains)
regardless of their slope, or it can be raised high enough at pumping stations so that
gravity provides the required velocity.
(2) Operation. Nonclogging centrifugal wastewater pumps are most
satisfactory for pumping wastewater. Pumps are usually set in pairs to give 100 percent
standby service during maximum flow. When the wastewater in a sump reaches a
predetermined depth, a float switch starts a pump. When the sump is almost empty, an
automatic switch stops the pump. The starting-switch control of the standby pump is set
to start at a slightly higher water level than the first pump and to stop at the same low-
water level. Starting switches are set so that pumps operate alternately, or the switch
mechanism is changed at frequent intervals so that each pump operates about the
same length of time. Pump motors are located so they will not become flooded if they
fail to function or a shutoff valve is provided to stop the flow when the water level
endangers the drive unit. Pump stations may be entirely manually controlled.
(3) Maintenance. Proper maintenance assures efficient operation and
avoids breakdowns. Breakdowns may cause health hazards by backing up wastewater
in buildings or flooding low areas. Odors from lack of cleanliness in pumping stations
located in housing areas are especially objectionable. Improper ventilation of the pump
house will allow accumulation of acid-laden condensate from wastewater that severely