Water Lifting Devices
----------------------

Pumps


• Pump is a machine that lifts water from source (open wells, tube wells or deep wells) to ground surface.

Pumps are generally two types:

1) Indigenous water lifts
2) Highly efficient irrigation pumps


Principles involved in pumping water from source

• Atmospheric pressure – (force per unit area exerted on a surface by the weight of air above that surface in the atmosphere of Earth) 101.325 kPa
• Positive displacement – (makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe)
• Centrifugal force – (outward force that draws a rotating body away from the center of rotation)
• Movement of columns of water caused by difference in specific gravity


Centrifugal pumps

• Most commonly used for irrigation purpose
• Usually give efficient operation over relatively wide range of operating conditions especially if the total head exceeds 4 meters
• The centrifugal pump draws water from the source of supply to the pump. Therefore, its use is limited to locations where this distance is within the limits of suction.
• Where this limit exceeds, horizontal centrifugal pumps cannot be used and deep well turbine pumps or submersible pumps should be used.


Principle of operation of centrifugal pump

• The impeller is rotated at high speed by an electric motor or an engine.
• As soon as the impeller starts rotating, the blades cause the water to rotate with the impeller and impart high velocity to the water.
• Hence, water in the impeller (filled up by priming in the beginning) moves from the eye (centre of the impeller) to the periphery
• Negative pressure is created at the eye due to which water rushes from the water source to the eye or outside the casing where pressure head is built up
• The static water in the well is at the atmospheric pressure, so the water rushes into the suction pipe due to difference of pressure
• In this way, continuous flow of water is maintained in the pump
• The centrifugal pump so called because the pressure increases with in the casing due to centrifugal forces
• The pump will not work until the casing and the suction pipe are full of water by priming.


Cut section of Centrifugal Pump

Double Suction Centrifugal Pump
Classification of centrifugal pump

• Type of energy conversion: (a) volute, and (b) diffuser
• Working head: (a) low lift, (b) medium lift, (c) high lift
• Number of impellers per shaft: (a) single stage and (b) multi-stage
• Relative direction of flow through impeller: (a) radial flow, (b) mixed flow and (c)axial flow
• Type of suction inlet: (a) single suction and (b) double suction
• Axis of rotation: (a) horizontal and (b) vertical
• Impeller types: (a) closed impeller, (b) semi-open impeller, (c) open impeller
• Method of drive: (a) direct coupled, (b) gear-driven and (c) belt-driven


Vertical turbine pumps

• A vertical turbine pump, also called a deep well turbine pump, is a vertical axis centrifugal or mixed flow type pump
• It operates on the centrifugal principle but differs from ordinary centrifugal pump because the water thrown from the periphery of the impeller blades is directed upward by stationary guide vanes surrounding the impeller
• For high lifts, several impellers placed in series with each successive bowl attached directly one above or below
• The bowl are so designed that the water discharge from a lower impeller is directed vertically upward to the centre of the next higher impeller.
• The vertical turbine pump consists of number of rotating impellers are arranged in series to create high head.
• Total head developed is proportional to the number of impellers (stage).
• The vertical turbine pumps are specially adapted to tube wells, where the pumping water level is below the practical limits of a volute centrifugal pump.
• higher initial cost and difficult to repair and install as compared to volute centrifugal pump

Submersible pumps

• A vertical turbine pump close coupled to a small diameter submersible electric motor is termed a submersible pump, in which both motor and pump are installed inside the well
• The motor is fixed directly below the intake of the pump.
• The pump element and the motor operate under submerged condition.
• It can be used in very deep tube well where a long shaft would not be practical.


Centrifugal Pump Working