Pumps are hydraulic machines designed for transmitting fluids under a head. By transforming the mechanical energy of the driving motor into the mechanical energy of the moving fluid, pumps lift fluid up to a specified elevation, deliver it over the required distance at the horizontal plane or make it circulating in a certain closed system.

Pumps, performing one or several of the mentioned functions, form a part of pumping station equipment one way or another. An electric motor connected to the power grid is used to drive the pump. Water or another working fluid is taken from the lower basin by the pump and pumped over the pressure pipeline to the higher basin transforming the motor energy into the fluid energy. The energy of the fluid after having passed through a pump is always greater than that prior to passing through the pump.

The key parameters of pumps which determine the variation range of pumping station operation mode, its equipment configuration and design features are pressure (discharge head), discharge (delivery rate), capacity and efficiency.

Pressure (discharge head) implies a fluid specific energy increment in the section from the pump inlet to outlet. Pump head determines the lifting height (vertical head) or range of fluid transmission and is stated in meters.

Discharge (delivery rate) is characterized by the fluid volume supplied by a pump to a pressure pipeline per unit of time; it is generally expressed in m³/s, l/s, or m³/h. The pump capacity expressed in kW determines the driving motor capacity and total (installed) capacity of the pumping station.

Efficiency takes into consideration all types of losses associated with transformation of motor mechanical energy into the energy of moving fluid by the pump. The efficiency determines the financial viability of pump operation with its other parameters (pressure, discharge, capacity) varying. The history of the appearance and development of pumps shows that they initially were used only for water lifting purposes. But at present their application range is so broad and diverse that it would be one-sided to introduce them as water-pumping machines only.

Structure and operating principle of impeller pumps

Among the impeller pumps produced in lots by the domestic industry and widely used for constructing modern systems of water supply and sewerage are centrifugal, axial-flow, and angular-flow pumps. These pumps’ operation is based on the common principle: force interaction between impeller blades with the flow of the pumped fluid around the impeller. However, the mechanisms of such interaction for the mentioned pump types differ from one another, which for sure will result in considerable differences in their designs and operating characteristics.

Centrifugal pumps

The main working member of the centrifugal pump is represented by an impeller that freely rotates in the pump casing and is slipped on the pump shaft. The impeller consists of two disks (front and back) spaced at some interval apart. There are vanes between the disks connecting the latter into a singe structure; the vanes are smoothly turning to the side opposite to the direction of the impeller rotation.

The internal surfaces of the disks and the vane surfaces form so-called impeller intervane channels which are filled with pumped fluid during the pump operation. When the impeller rotates, centrifugal force acts onto every part of the fluid (of mass m) in the intervane channel at distance r from the shaft axis.

Under the action of this force the fluid is ejected from the impeller; as a result, depression (vacuum) occurs at the impeller center and higher pressure develops at its peripheral part. To provide continuous movement of fluid through a pump, it is necessary to ensure supply of the pumped fluid to the impeller and diversion of it from the impeller. The fluid is fed through a hole in the front disk of the impeller through a foot/suction pipe and a suction pipeline. Fluid movement through the suction pipeline is caused by the difference of the pressures above the fluid free surface in the reception basin (air pressure) and at the central part of the impeller (vacuum).

For diversion of the fluid, there is an expanding scroll casing (in the form of volute/elbow) in the pump chamber, where the fluid ejected from the impeller flows in. The scroll casing (connector bend) is connected to a short delivery space (diffuser) forming a discharge pipe which is generally connected to a pressure pipeline. Analysis shows that the higher the impeller rotation velocity and diameter, the higher the centrifugal force and, consequently, the pressure generated by the pump. Any high-speed motor can be used as a drive of the centrifugal pump. Most frequently, electrical motors are used for this purpose.

Depending on required parameters, purpose and operating conditions a large number of different designs of centrifugal pumps, which can be classified by several characteristics, is developed at present.

Depending on the number of impellers, there are single-stage and multistage pumps. In multistage pumps, the pumped fluid passes successively through a series of impellers slipped over a common shaft. The pressure generated by this pump is equal to the sum of the pressures generated by each impeller. Depending on the number of impellers (stages), pumps can be of double-stage, three-stage, etc. types.

Depending on the method of fluid delivery to the impeller, they distinguish end-suction pumps and double-suction pumps or so-called centrifugal double-entry pumps.

Depending on the method of fluid diversion from the impeller, there are volute pumps and turbine pumps. In volute pumps, the pumped fluid from the impeller flows directly to the scroll case and then it is either diverted into the pressure pipeline or goes to the following impellers by downpipes. In turbine pumps, the fluid prior to coming to the scroll case passes through the system of fixed vanes which form a special device called a guide vane. Depending on the layout of the pumping unit (shaft position), they distinguish horizontal and vertical pumps.

Depending on the type of connection with the motor, centrifugal pumps are divided into driven pumps (with a pulley or reducer), which are coupled directly with the motor by means of a clutch, and unit construction pumps, the impeller of which is slipped over the oblong shaft end of the electrical motor.

Depending on the pumped fluid, there are water supply pumps, sewage pumps, heating (for hot water) acid pumps, soil pumps, etc.

Axial-flow pumps

The impeller of an axial-flow pump consists of a bush with several vanes mounted on, representing aerodynamically-shaped curved blades with a rounded leading edge running against the stream. Pump impeller rotates in the tubular chamber filled with pumping liquid.

Under the dynamic impact of the vane on the fluid its velocity changes and as a result the pressure above the vane increases, while beneath the vane lowers. Thanks to the lifting force occurred at that the major part of the fluid at the range of the impeller moves axially, which is the reason for such a pump name. Moving progressively, the pumped liquid is at the same time slightly made to rotate by the impeller. A compensation device is used to eliminate such rotary flow of the fluid, through which the fluid passes prior to outflowing to the elbow offsets connected to the pressure pipeline.

The fluid is brought to the impellers of small axial-flow pumps by means of egg-shaped pipe. For this purpose, large pumps have chambers and suction pipes of rather complex form. Two designs of axial-flow pumps are produced: with impeller vanes fixed tightly on the hub and with adjustable vanes. Change of the impeller vane pitch angle within a certain range allows keeping high efficiency of the pump within a wide range of its operating parameters.

Synchronous and asynchronous motors connected directly with pump coupling are generally used as drives for axial-flow pumps. Pumping units are manufactured with vertical, horizontal and inclined shaft.

The efficiency of high-capacity axial-flow pumps comes to 0.9 and more.

Angular flow pumps

The fluid flow passing through the impeller of an angular-flow pump is directed not radially like in centrifugal pumps and not in parallel to the axis like in axial-flow pumps, but aslant as if along the diagonal of the rectangular formed by radial and axial directions.

Inclined flow direction establishes the following principal structure property of the angular-flow pump: the impeller vanes’ position is perpendicular to the meridian flow and inclined to the pump axis. This allows using combined action of lifting and centrifugal forces for generating a pressure (head).

The impellers of angular-flow pumps can be of closed or open type. In the first case, the impeller’s design is similar to that of the centrifugal pump impeller’s design; and in the second case, similar to the axial-flow pump impeller’s design.

The vanes of open-type impellers of a number of pumps are made rotary, which is their obvious advantage. The fluid is diverted from the angular-flow pump impeller through a scroll case like in centrifugal pumps or through a tubular elbow like in axial-flow pumps. According to their operating parameters (capacity, pressure), angular-flow pumps hold the intermediate position between centrifugal and axial pumps.

Source: Karelin, V.Ya., Minaev, A.V. Pumps and pumping stations. Moscow, “Stroyizdat” Publishing House, 1986 (in Russian)

Pumping station: configuration and functionality

The pumping station consists of water intake structures for suction pipes of pumps, the pumps themselves, motor, gear from motors to the pumps, pressure pipeline transporting water from the pumps to water-discharge device, etc. Thus, the conception of a pumping installation includes all the components of the operation depends the pump performance.

The pumping station includes: some components of pumping installations, station building itself, particular machines and facilities control units located in the building, and auxiliary equipment. Thus, pumping station in addition to components of pumping installations includes also machine control components.

Waterworks facility of the pump irrigation system

Waterworks facility of the pump irrigation system represents a complex composed of structures for water intake, water delivery to the pumping station building, pumping station building itself, pressure pipelines and constructions for reception of the water pumped.

Structures of the waterworks facility

Some constructions of hydrosystems are set approximately in the following sequence:

• construction of water-intake installation (aka water-intake structure), which withdraws water from a water supply source;
• facilities for water transportation from the water intake structure to the pumping station (open channels, pipelines);
• intake chamber in front of the pumping station building for water delivery to the it through an open channel; intake chamber represents a wider section of the canal before the pumping station building which includes conjugation structures of the canal and building;
• pumping station building;
• pressure pipelines;
• water-discharge facilities for receiving the water outflowing from the pipeline (e.g., head pond of pumping main canal of the irrigation system).

According to their functions, pumping installations and pumping stations can be broken down into the following types:

• melioration pumping installations and stations intended for lifting water to an area reclaimed (or irrigation systems) or for water diversion from a reclaimed area (drainage and irrigation systems); in the latter case, they are used for pumping-over of waste or drainage waters;
• sprinkling pumping installations for irrigation of crops by sprinklers;
• 1st and 2nd elevation pumping stations intended for drinking water supply and agricultural technical requirements;
• sewage pumping stations for pumping-over of faecal and industrial waste waters;
• pumping installations used in irrigation and drainage construction works;
• auxiliary pumping installations.

Source: www.donmetall.ru