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Chapter: Environmental Engineering - Collection and conveyence of water

Pumps And Pumping Stations

Pumps And Pumping Stations
Index : PURPOSE, Classification of Pumps, FACTORS AFFECTING THE SELECTION OF A PARTICULAR TYPE OF PUMP, HEAD POWER AND EFFICIENCY OF PUMPS, ECONOMICAL DIAMETER OF THE RISING (PUMPING) MAIN, LEA FORMULA, RIGOROUS ANALYSIS

PUMPS AND PUMPING STATIONS

 

PURPOSE

 

I.                   To lift the water from source to the treatment plant which is at higher level compared to the source

 

II.                To lift the treated water to the elevated tanks

III.             To increase the pressure in the distribution system.

 

IV.    To lift the water at the treatment plant if sufficient natural ground slope is not available as to cause gravitational flow between different units of treatment plants.

 

Classification of Pumps

 

Based on their Principal of power required

 

i. Displacement pumps

ii.Centrifugal pumps

iii. Airlift pumps

iv. Impulse pumpsiv.Diesel engine pumps

v. Stand by pumps

 

Based on the type service

 

i.Electrically driven pumps

ii. Gasoline pumps

iii. Steam engine pumps

iv. Boosters

 

Based on the type of operation

 

i.  Low lift pumps

ii.High lift pumps

iii.Deep well pumps

 

Under most of the situations in water supply scheme, displacement and centrifugal pumps are commonly used.

 

Displacement pumps

i.                   Reciprocating pumps

ii.                 Rotary pumps

 

PUMPING STATIONS

 

The location of a pumping station is primarily governed by the place where it is to recerive water. The points to be kept in mind while selecting a suitable site are.

 

 

i.                   The site should be away from all the sources of contamination or pollution

 

ii.                 The site should be above the HFL of the river.

 

iii.              Its future growth and expansion is easily possible

 

iv.              Possibility of fire hazards is also to be considered

 

 

FACTORS AFFECTING THE SELECTION OF A PARTICULAR TYPE OF PUMP

 

1.     Capacity of pumps

 

2.     Importance of WSS

 

3.     Initial cost of pumping arrangement

 

4.     Maintenance cost

 

5.     Space requirements for locating the pumps

 

6.     Number of units required

7.     Total life of water required

 

8.     Quantity of water to be pumped.

 

 

HEAD POWER AND EFFICIENCY OF PUMPS

The total head against which a pump works is made up of

 

i.                   The suction Head(Hs)

 

ii.                 The Delivery Head(Hd)

iii.              The Head loss due to friction entrance and exit in the rising main(Hf)

 

The suction HEAD is the difference in elevation between the low water level and center line of pump.

 

Delivery HEAD is the difference in elevation between the pump center line and point of discharge

 

Total HEAD (H) =Hs+Hd+Hf

 

The work done by the pump in lifting Q? cumecs of water by a head(H) =WQH kg-m/sec. Where,

 

W = Specific weight of water, 1000 kg/m3 Q = discharge to be pumped, m3/sec.

 

The water horse power of the pump is given by

WHP(out put) = WQH/75

If n? is the efficiency of the pump then

 

BRAKE HORSE POWER of the pump is given by

BHP(INPUT) + WQH/75n


ECONOMICAL DIAMETER OF THE RISING (PUMPING) MAIN

 

The economical diameter is a particular size of the pumping or rising main which while passing a given discharge of water gives the total annual expense to be minimum.

 

If the diameter chosen is more than the economic dia, it will lead to higher cost of the pipe line on the other hand, if the dia of the pipe is less than the economical dia, the increased velocity will lead to higher friction headless and require more HP for the required pumping and the cost of pumping shall be much more than the resultant saving in the pipe cost.

 

LEA FORMULA

An empirical formula given by LEA

 

Connecting the dia and discharge is given by

D = 0.97    to       1.22 SqRt(Q)

Where

D = economical diain m

 

Q = Discharge to be pumped in  cusecs

This relation gives optimum flow velocity varying between 0.8 to 1.35m/sec

 

FOR RIGOROUS ANALYSIS The total cost of pipe and pumping should be woeked out at different assumed velocities (b/w 0.8 to 1.8m/sec) and a graph plotted between the annual cost and the size of the pipe. The economical size is one which gives the least annual cost.

 

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