Pump Types

Centrifugal pumps are used almost exclusively in drainage and irrigation installations. Because of the large selection of propeller, volute, turbine, and portable pumps manufactured today, there is little difficulty in finding a pump that will meet the conditions encountered in these fields. Pumps in the sizes needed to meet the requirements of the majority of installations are available as standard items. Specialized pumps and extremely large pumps are designed and built to meet the needs of individual projects.

Propeller Pumps These units are used for low-head pumping. As most of the pumping in drainage and irrigation is low-head, the propeller pump is the most widely used type. In general, vertical single-stage axial- and mixed-flow pumps are used; however, there are instances where two-stage axial-flow pumps should be considered for economic reasons.

Horizontal axial-flow pumps are used for pumping large volumes against low heads and usually employ siphonic action when not of the submersible type. When higher heads are involved, these pumps can be arranged to operate with siphonic action until the back pressure places the hydraulic gradient above the pump.

Variable-pitch propeller pumps rotating at constant speed can be operated efficiently over a wide range of head-capacity conditions by varying the pitch of the propeller blades. These pumps are used when the head-capacity conditions cannot be met with the more economical fixed-blade pumps and where the pumps will be operated often enough and long enough to warrant the expense. The blade-control system needed for such pumps is more sophisticated than in any of the systems usually provided on drainage and irrigation projects. As a consequence, operation and maintenance must be performed by organizations employing competent and experienced personnel.

Volute Pumps Volute pumps are used when pumping from surface sources and in general when the total head exceeds approximately 45 ft (14 m). Such pumps are available in many types, such as vertical and horizontal shaft, end suction, bottom suction, and double suction with semi-open or closed impellers, and so on. These pumps are mounted in dry pits when located below grade and on slabs or floors when located above grade. The particular type used depends on the capacity and kind of service to be performed.

Deep-Well Turbine Pumps Deep-well turbine pumps (vertical-shaft, single-suction pumps having one or more stages) are used in irrigation primarily to pump water from a subsurface source into a distribution system. The head against which the pump will operate determines the number of stages that must be provided. For large capacities, more than one pump will be needed.

Submersible Turbine Pumps In these deep-well units, the motor is close-coupled to the pump and submerged in the well. This type of pump is used for high-head applications where long intermediate shafts are undesirable.

Portable Pumps In drainage work, portable pumps are used as emergency equipment to control ponding elevations where mobile equipment, such as tractors and trucks, having power takeoffs are available to drive them. In irrigation work, they are usually used to irrigate from a surface source. Such pumps are small-capacity, low-head, economical pumps that must be submerged in order to be used.

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