Friday, January 18, 2013

The Centrifugal Pump

Arakavathy ; Vrishabavathy and Kumudavathy are rivers that can be associated with Bangalore. They take their birth in the Nandi Hills and flow through the plains of Bangalore and ultimately connect with the Cauvery near Kanakpura called Sangam. Bangalore they say must be having a population today of some six Million. The need for centralized system for water was felt long back and some kinds of dams like the one seen at Heseghatta were set up on these rivers and water supplied to the city..thereby these rivers began to loose their original identity of rivers and become some kind of conduit for waste to flow out of the city in  some form of a natural drain. Note that on the banks of these rivers as they flowed past the city there were temples set up and for example the temple in Ulsoor is on the banks of one such rivulet and another seen on Mysore road. The Kings of yore found these as ideal settings to set up temples. I have enjoyed the silent flow of one of these rivers inside SAI the Sports Authority of India campus on Mysore road..contaminated water flowing in the form of a river....If any of the kings of yore were to take a look at the state of these rivers today they would weep. But changing circumstances have had their spell on Bangalore.

Reservoirs like Hesserghatta and Tippagondanahalli find it difficult to meet water demands due to diminishing rains and the river Cauvery some 90 miles away is slowly becoming a source of water for the City..pumping of water through tens of miles and BWSSB has been doing a good job.  The terrain of Bangalore is one of hills and planes if one studies it; and the ground-water situation is much better in the planes than in the hills.

The above is a recent photograph of the reservoir or lake at Heserghatta called heserghatta lake made using mud-dam technology.

How does the BWSSB water circuit work..largely pumping water into underground sumps of house-holds from where they are pumped into an over-head tank within the residential facility and this pumping has to be done periodically as the water level in the tank declines a repetitive activity largely done by small centrifugal pumps or vacuum pumps..but largely centrifugal pumps.

Centrifugal pumps are an interesting technology that works as a reverse Francis turbine and is a complex and sophisticated Industrial pumping technology. It basically has a motor connected to an impeller all housed in a closed chamber and as the motor rotates it creates suction and note that initially charge must be poured into the down stream and create connection between the motor and the charge..more precisely the pump and the charge.The charge is prevented from flowing down into the tank by a hydraulic device called the foot-valve. When the motor rotates suction is created releasing the foot valve and charge flows into the chamber and centrifugal or tangential force created by the impellor pushes the water upward or the charge upward on a continuous basis.

Note that as the system works water rushes into the chamber and any suspended particles can jam or stop the impeller and this happens on a continuous basis needing periodic cleaning of the impeller a disadvantage of this system.

For long I confused a Centrifugal pump with a Vacuum pump. When we were students at NIT we had a lab in the III semester which was a composite of  Heat Engines, Fluid Mechanics and Hydraulics. During the strike in 1983 some disgruntled students entered the Hydraulics lab and removed the turbines and other equipment and dumped them in the well near-by and we never got a chance to work on Hydraulics and now with the various support systems on the Internet I am trying to understand Hydraulics..what a pity?

People who use such pumps must get the device serviced regularly largely getting the impellor cleaned to prevent down time in water supply.

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