3 August 1998
RAW WATER PUMPING FACILITIES
8-1. SURFACE WATER SOURCES.
a. Pumping Station Arrangement. The location and arrangement of raw water pumping
stations will depend upon the requirements of the local situation and only general comments
can be given. Raw water pumping stations and intakes are often combined in a single
structure, but this is not mandatory. The depth of the structure is a function of the type and
arrangement of the pumps used. Horizontal centrifugal pumps are often employed and will
give satisfactory performance and good operating economy. However, if the supply is from a
variable stream and the pump suctions are to be under positive pressure under all operating
conditions, a station of considerable depth probably will be required. Deep stations of the
dry-pit type commonly used for horizontal centrifugal pumps should be compartmented so that
rupture of pump discharge piping within the station will not flood all other pumps and motors.
The depth may be reduced, with some loss in reliability, by installing the pumps at an elevation
such that suction lift prevails under some operating conditions. Equipment for priming is a
requirement when suction lift is employed. Use of vertical type wet-pit pumps, which requires
less space in plan, permits a somewhat shallower station and does not require priming, may
prove an economical alternative. Among other pumping arrangements that could be used are:
vertical-type pumps or end- or side-suction centrifugals, with their shafts in a vertical position,
located on a submerged suction header. The latter permits location of the pump drive units at
an elevation where they are protected from flooding and readily accessible.
b. Pump Protection. Pumps, particularly those located on streams, must have
protection against debris. In order to prevent or at least minimize screen clogging, the size of
the screen openings should be consistent with the capacity of the pump to pass solids. The
pump manufacturer can supply information on the largest sphere that the pump will pass.
Plants with flows of 3.8 million liters per day (1 mgd) or larger and obtaining their water from
streams will use hydraulically cleaned traveling screens. For smaller installations or those not
obtaining water from streams, a fixed bar screen or strainers can be used. For such
arrangements, provision must be made for cleaning. This can be accomplished by
backflushing. In general, screening should be held to the minimum required for protection of
the pumps. Excessively fine screens, strainers or bar racks are sometimes subject to rapid
clogging and will require frequent cleaning. Debris removed by mechanically cleaned screens
must be collected and hauled to a landfill or other acceptable disposal site. Screenings may
be stored temporarily at the station in dump carts from which they are discharged to a truck for
transport to a disposal site.
c. Structural Considerations. Substructures will usually be of reinforced concrete.
Superstructures should be of incombustible materials such as reinforced concrete, brick or
other masonry. Wood frame construction should not be used except for temporary or minor
installations. Structural design should include consideration of requirements for pump and
motor servicing and removal for major repairs.