LIFT IRRIGATION

LIFT IRRIGATION SCHEMES

MAJOR TOPICS RELATED TO L.I. SCHEME

1.REASONS FOR OPTING L.I. SCHEMES OVER GRAVITY SYSTEM

2.LIMITATIONS OF L.I. SCHEME

3.VARIOUS COMPONENTS OF L.I. SCHEMES

4.TYPES OF PUMPS / PUMPS HOUSES

5.STAGES OF PLANNING  &  DESIGN

6.DESIGN OF PUMP

7.DETERMINATION OF PUMPING HEAD

8.DESIGN OF INTAKE AND JACKWELL / SUMP

9.GENERAL ARRANGEMENT OF PUMP HOUSE

10.DESIGN OF PUMP HOUSE

11.DESIGN OF PRESSURE MAINS

12.IMPORTANCE OF SURGE PROTECTION DEVICES 

Why Lift Irrigation:

1)Rain is decentralized and so is the demand. But the supply has not been decentralized.

2)Perennial drought conditions in some pockets

3)Many upland areas starve for water

4)In the prevailing situation, the gap of socio-economic conditions between  the regions is getting widened causing imbalance w.r.t. economy as well as development.

5)Though Dams & barrages able to meet most of the requirements, due to obvious reasons given below, LI Schemes assumed greater significance and gained momentum to narrow the gap of socio-economic conditions between the regions

Dams & Barrages have inherent and never ending problems of :

1)Submersion

2)Rehabilitation

3)Land Acquisition

4)Environment Clearance

5)Inter-state disputes and

6)Most importantly they are time consuming by taking many years / some times decades for completion.

7)Due to the above problems, the major irrigation structures require very huge financial support and often, the estimated costs gets multiplied due to delay in the completion causing escalation of prices.

8)Further, there are some upland areas which unable to get water, even after having a major dam in the vicinity due to various reasons.

Reasons for Opting Lift Schemes Over Gravity System

1)In the present circumstances, lift irrigation schemes assumed greater significance and seems to be the only viable solution to meet the aspirations of the upland people for the following reasons :

2)Speedy Completion of the Scheme

3)Lesser initial Cost

4)No need of extensive and time investigation

5)Flexibility of Location of Head works

6)Does not have foundation problems

7)Absence of problems in dams such as Submersion, Environment Problems, Rehabilitation & Land Acquisition Problems and Inter-state Disputes.

Though lift irrigation schemes have some drawbacks and are costly, in the prevailing situation, they are inevitable since the situation demands them in the contemporary irrigation planning.LI schemes are going to play vital role in the inter linking of rivers.

Limitations of L.I. Scheme 

They are costly w.r.t. benefit cost ratio compared to other irrigation schemes / Gravity schemes                  

1)Require assured un-interrupted power supply

2)Require assured flows from the source

3)Recurring cost on power bills

4)Regular maintenance is required for civil as well as mechanical works

5)Life of L.I. scheme is shorter than dams & barrages

6)Needs periodical replacement of mechanical & electrical components

In spite of  above drawbacks, to bridge the gap between developed areas and un-developed areas with reference to socio-economic conditions and the vacuum created by the absence & non-provision of dams & barrages, lift irrigation schemes are ought to be taken up judiciously which lessens the apprehensions of the farmers

VARIOUS COMPONENTS OF LI SCHEMES 

1)Pumps

2)Intake / Sump

3)Pump house

4)Pressure mains

5)Surge Protection Devices

6)Approach Canal

7)Delivery Cistern

8)Gantry for Pumps, Stoplogs & Trash racks

9)Control Panels etc.,

VARIOUS TYPES OF PUMPS AND PUMPS HOUSES 

Pump is the HEART of the LI Scheme.

A designer should have sound knowledge of various types of pumps that are available in the market, their applicability and limitations to achieve economy without sacrificing the performance of pumps. Depending upon the type of pump and its limitations, number & specifications of the pumps shall be finalized. 

Various types of Pumps that are used for irrigation purpose  are:

1)Submersible Pumps & Polder Pumps

2)Horizontal Centrifugal Pumps

3)Vertical Turbine pumps

4)Concrete Volute Pumps ( Dry Pit Pumps )

5)Francis Turbine Pumps ( Dry Pit Pumps ) 

Preferable Conditions for Adopting Various Pumps

Horizontal Centrifugal Pumps

1)Suction Lift shall be less than 6.0m and HP of pump is within the manufacturing limits ( Approx 4000 HP).

2)Discharge and the pumping head are within the limits to suit the capacity of pumps.

3)These pumps are best suited for lifting from canals or from tanks with shallow depth of water.

Vertical TurbinePumps

1)When the suction is more than 6.0m

2)When the discharge is considerable and some times suction is less than 6.0m and requiring many no. of  horizontal pumps, then VT pumps may also be provided.

3)May be adopted when the discharge of pump is less than 3 cumecs and total pumping head is less than 75.0m

4)When the fluctuation of water levels in the source / river is more than 25.0m, these pumps are not desirable

5)Max manufactured HP of pump is 4000 HP only

Concrete / Metallic Volute Pumps 

When the discharge is more than 3 cumecs and less than 10 cumecs with pumping head upto 75.0m Concrete volute are preferable and Metallic volute are preferable when the head is between 75.0m to 150m

1)When fluctuation is more than 20.0m, these are preferable over VT

2)For HP of pumps more than 4000 HP

Francis Turbine Pumps

1)All concrete volute conditions

2)Best suited when the discharge is more than 10 cumecs and head more than 100M

PLANNING & DESIGN ASPECTS

1)Until now the L.I. Schemes are proposed for smaller discharges, head & magnitude, but with the improved technology and developments in the field, major L.I. schemes with huge magnitude, discharge & head are going to play a decisive role in irrigation in coming days.

2)Planning & design of lift irrigation schemes needs proper attention as any defects would lead to unsatisfactory performance with reduced efficiency of the system. For effective and efficient function of a L.I. scheme, the designer should have sound knowledge in planning & design of L.I. schemes.

3)More attention is needed in finalization of H.P.’s and design of various components for the L.I. schemes  comprising series of pumping stations or multi stage lifts and with intermediate ayacut, as all the pumping stations are to be well synchronized as well as synthesized. 

Stages of Planning  &  Design of L.I. schemes 

1. Finalization of the Alignment w.r.t

Balancing Reservoir

Location of Pumping Stations

Length of Pressure main

Pumps

Gravity Canal

2. Design of Hydraulic particulars w.r.t

Design Discharge

Approac/ Intake canal

Delivery Canal

3. Design of Pumps and Pressure mains

4. Design of Intake and Jackwell/sump

5. Design of Pump house

6. Design of Delivery Cistern & Gravity canals

Finalization of the Alignment

While choosing the alignment, the following points are to be duly considered to the extent possible

1) As much as possible, shorter length of the pressure mains shall be adopted as lengthy mains have bearing on the pumps as well as on the cost of the scheme

2)To the extent possible, greater length of gravity canals shall be adopted to reduce the length of pressure mains

3)Alignment with smaller length of approach / intake canal from the source to the pump house shall be explored to minimize the maintenance problems

4)At the off-take point of approach canal, there should be assured flows from the source to meet the requirements

5)It is desirable to have minimum number of lifts with greater length of gravity canal in between the lifts as more number of pump houses increases the cost of civil, electro-mechanical arrangements etc., 

Additional pump house in the Alignment

Introduction of additional pump house reduces length of pressure mains & increases length of gravity canals, the scheme may be economical as capital cost on pressure mains, water hammer devices and pumps may be reduced as well as cost on power bills may comedown. 

1)When the total lift ( including losses ) is more than 100.0m and the discharge of each pump is more than 5 cumecs, then second stage of pumping may be necessary.

2)Limitation of pump capacities have bearing on the number of lifts.

3)Greater length of the pressure mains with huge heads has implication on the cost of the scheme and needs Increase of thickness and Provisions for water hammer devices.

(There is a need for working 2 or 3 alternatives particularly where there is huge head & lengthy pressure mains are involved. Cost economics shall be worked out for different alignments from which best and economical alignment should be explored. Hence, the alignment should be judiciously decided in fixing the lengths of the pressure mains, gravity canals, number of lifts and pumps)

Balancing reservoir in the Alignment

Proposal of introducing a reservoir  ought to be considered if the site conditions permit or utilizing the existing tank  in between the lifts. Advantages of reservoir / tank in between the lifts are : 

1)The design discharge will be less than the discharge required to meet the peak period of crop.

2)With the reduced discharge, pump capacities, sizes of pressure mains, pump house sizes and canal sizes will also be reduced resulting in the considerable economy.

3)Usually L.I. schemes are proposed for pumping flood water and hence by introducing a balancing reservoir, the water can be preserved for later usage as and when required to suit the cropping pattern.

4)Multi stages of lifts need proper synchronization of all the stages of lifts. Failure of any single stage, makes grinding halt to all the lifts, but with a balancing reservoir, the above problem can  overcome as it will act as a buffer.

Intake Location: 

Precautions in locating the intake structure at source

1)Bed level of the approach canal shall be kept above the source bed level

2)Line of intake shall be normal to the axis of the pump house.

3)There shall be a driving head to draw water from source to intake

4)Intake structure shall be sited in river source regions at  low sedimentation

5)Intake canal shall be located where the river flows in straight line.

6)Intake structure shall be located nearer to the contour 2.0m above MWL/FRL of the source to have smaller length of approach road.

7)Intake shall be sited where the low water level in the source is nearer by which smaller length of intake canal will be required.

8)When the source is unapproachable or the alignment is passing through a restricted area ( protected forest area ), then a tunnel can be thought off instead of intake canal ( as done in AMRP ). Also as it was found that tunnel is cheaper than the pressure main, the pump house is shifted further to D/S in order to reduce the pressure main length and increase the length of tunnel

Finalisation of Hydraulic Particulars 

Proper design of hydraulic particulars is most important aspect for good functioning of L.I. scheme which improves the efficiency of the scheme. The design of hydraulic particulars comprises of the following : 

1)Crop water requirement :

The crop water required for recommended crop type & pattern and its period of operation ( or crop period & wettings ) shall be obtained. Quantity of water required for each wetting of the crop is to be computed.

2)Seepage & Evaporation Losses :

After knowing the length of canals and the capacity of the reservoirs in between if any, the seepage & evaporation losses are to be computed.

3)Design Discharge of Pumping:

Total quantity of water to be pumped in the specified period shall be arrived by the summation of crop water requirement, seepage & evaporation losses and drinking water if any. From the total quantity of water and the proposed period of operation w.r.t. crop period, the design discharge can be computed.

Whenever there is no intermediate reservoir, the design discharge shall be w.r.t.  peak period during which the crop requires max. water. But whenever any reservoir is present, a mechanism has to be worked out depending upon the reservoir capacity and crop requirement in such a way that making use of the reservoir the design discharge can be minimized, which makes the scheme more economical.

Pumping hours :

The L.I. schemes will be provided dedicated power lines and hence the pumps shall be designed for 24 hours operation except in special conditions. If they are designed for 20 hours pumping, the cost of the project increases by 20% and so on. Pumping hours has the bearing over the HP’s and obviously on the cost of the scheme.

Intake / Approach Canal :

The intake canal shall be designed for the design discharge such that it draws full discharge at the lowest water level ( LWL ) of pumps i.e., the level below which pumping will not be done and the availability of required water during the period of operation in source at the level shall be ascertained.

Delivery Canal

As the lift water is precious, lined canals may be proposed for the conveyance to the field channels.  

Design Of Pumps 

1)Pumps are important components and function as heart of the L.I. scheme and play vital role in the performance of the scheme.

2)Any wrong selection of pumps may lead to procurement of unsuitable pump and the scheme always may face threat of pumps repair & maintenance.

3)It is not desirable to have casual approach in the design & selection of pumps. 

Design of pumps involves

1)Finalisation of Data required for Pumps Design

2)Finalisation of types Of Pumps ( Keeping in view the application & limitations of various types )

3)Freezing Number of Working Pumps

4)Calculation of Pump Capacities / Parameters

Data Required for Pumps Design 

To takeup the selection & design of pumps, the following data is pre-requisit: Total discharge of the scheme to be lifted

1)Lowest water Level  ( LWL ) below which pumping need not be done

2)MFL / FRL / FSL of the river / reservoir / canal as the case may be. This helps in fixing the platform level and type of the pump based on the static head.

3)Delivery Level to which water is to be lifted.

4)Number and Length of pressure mains with type of material.

Determination Of Pumping Head 

Total pumping head shall be arrived with care since any wrong calculation has the bearing on the performance of the pump. Excess selection of head may lead to un-necessary increase in higher pump capacity and higher power consumption and lesser head may lead to non-functionality of the pumps to their efficiency.

Total pumping head is obtained on summation of :

1)Static head

2)Frictional losses in pressure mains

3)Losses due to exit, entry and bends

4)System resistance  losses due to the combined / operation of pumps and pressure main

Finalization Of Static Head

1)Static head is level difference between LWL / Avg Water level & delivery level ( For Optimization of pumping capacity and scheme economy, it is always desirable to design pumps with normal / average water levels instead of LWL).

2)Whenever elevation higher than delivery level is located before cistern, possibility of gravity flow in the pipe may be verified to reduce the pumping capacities, in which case the static head shall be w.r.t. the summit point.

Pump Capacity (HP Required) and Specific Speed of Pump 

HP Of pump can be calculated as given below

HP = 62.45 * Q * h / ( 550*efficiency )  ( FPS units ) Where Q = discharge in cusecs ; h = head in ft= 981 * Q  * h  / ( 75 * efficiency ) ( MKS units ) Where Q = discharge in cumecs ; h = head in m 

Specific speed can be calculated as given below:

Ns = ( 3.65 * N * Q 1/2 ) / H 3/4    ( MKS units ) Where  N = Rotative speed in rpm Q = discharge in cumecs; h = Total head in m Ns = ( N * Q 1/2 ) / H 3/4 ( F.P.S. units ) where Q = discharge in cusecs; h = Total head in ft

Speed of the Pump

The speed of the pump can be obtained from formula given below 

N   =120 f / n = 6000 / n 

1)Where   N =     Speed of the pump    

f = Frequency  ( In India, f  =  50 )    

n = Number of Poles in even no.

2)Various speeds to be considered in the designs are : 1500, 1000, 750, 600, 500, 428, 375 and 333.

3)Speed less than 333 may be ascertained from the suppliers.

Determination Of Pumping Head .

Total pumping head should be arrived with care since any wrong calculation has the bearing on the performance of the pump. Excess selection of head may lead to un-necessary increase in higher pump capacity and higher power consumption and lesser head may lead to non-functionality of the pumps to their efiiciency.

Total pumping head is obtained on summation of the following :

1)Static head between LWL & delivery level ( For Optimization of pumping capacity and scheme economy, it is always desirable to design pumps with normal water levels instead of LWL )

2)Frictional losses in pumping lines  and pressure mains.

3)Losses due to exit, entry and bends.

4)System resistance  losses due to the combined / operation of pumps and pressure mains.

(Design discharge shall be at average head,otherwise if kept at maximum head needs higher capacity of pumps and power consumption and results in higher discharge for average and low heads,necessiating higher canal sections and thus making the scheme uneconomical)

Determination Of Friction Losses

(Hazen William Formula) 

Hf = L ( 1.1778 V / C R 0.63 ) 1.852

Where V = Velocity in m/s

R = Hydraulic Radius in m

C = Hazen William Coeff based on type of material of Pressuremain ( Values for various types are given below ).

Hazen William Coeff For Various Types 

C = 100 For Unlined Metallic Pipes = 140 For Centrifugally Lined Metallic 

Pipes ( upto 1200 mm Dia ) = 145 For Centrifugally Lined Metallic

Pipes ( Above 1200 mm Dia = 110 For Cement Mortar Lined Metallic

Pipes  

= 140 For PSC Pipes ( upto 1200 mm Dia )

= 145 For PSC Pipes ( Above 1200 mm Dia )

= 145 For PVC, GRP & Other Plastic Pipes

Standby Pump 

Now a days, the provision for standby pumps is not being considered for the following reasons :

1)Previously, the pumps were with smaller capacities and were operated for 16 hours only. Hence to have continuity of the pumping for the required discharge, a standby pump was proposed in order to keep the pumps operation in rotation. However with the advancement of the technology in the pumps manufacturing, the pumps can be operated un-interruptedly throughout the required period and hence provision of standby is not necessary.

2)There is apprehension that any failure of single pump also hampers the design discharge and endangers the crop, but it is felt that with the improved technology, the frequency of pump’s break down is minimum and also it can be got repaired within a short period if attended in time.

3)High duty pumps does not get frequent repairs.

4)Further, the pumps will be designed for peak discharge corresponding to peak requirement of water, the duration of which will be max. of one month. During non-peak period all the pumps will not be in the operation and hence even if any pump gets repair in the non-peak period, there will be ample time to get the repair done without hampering the system. The chance of pump break down during the peak period is hypothetical and with the requirement of very short period for attending the repair, the risk of deletion of standby can be  taken for economy consideration.

5)Standby pump increases size of the pump house as well as jackwell which results in the increase in the capital cost proportionately and will not have any additional returns.

6)Sometimes Power billing may be done on standby pump also irrespective of usage or operation.

7)Due to regional and social problems, users  will tempt to make the standby also as working during the scarcity causing tampering of the system resulting in failure of projects in the vicinity , which may lead to regional quarrels.

8)However, as an precautionary measure, regularly required spare parts may be procured along with the Pumps for the replacement

Design of Intake and Jackwell / Sump 

The objective of sump is to provide good flow conditions to the pumps and to avoid cavitation, swirl and vortices in the flow, which damages the impeller. If the design is with poor geometric features, undesirable hydraulic conditions may occur in the sump which may have impact on the pump & efficiency.

1)The approach canal slope and driving head are to be designed such that the velocity of water at the intake of sump should not be more than 1.2m/s. The flowing water should not have velocity more than 0.3m/s at the location of pumps.

2)If the approach canal width is kept more than required, it reduces the length of the transition as well as the cost of the intake

3)Whenever the approach canal slightly silted up, it assures to realize design discharge by absorbing the silt if the same designed for higher Q(1.5Q). 

4)The intake / jackwell  width and intake canal width are connected by the bed slope of not more than 10⁰ in elevation and not be more than 20⁰ in plan.

5)Whenever any pump house is proposed on foreshore of any reservoir, a circular jackwell will be ideal as there is no need of provision for intake well as always minimum and stagnant water level will be maintained. However when the pump house is to be located other than in the reservoir, to make flow uniform & steady from intake canal to pump house, an intake well is needed. The intake well also functions as distributor of the flow uniformly & equally to the pumps.

6)As the steel cost is increasing rapidly, the stoplogs & trashracks can be  proposed upto LWL only with breast wall in between upto LWL from platform level. This economizes the scheme as well as improves the hydraulic performance of sump. Further, stoplogs need not be procured for all the vents and instead only for one vent may be sufficient as it may be  used during repair to the pump.

Dimensions of Jackwell/Sump for VT Pumps 
1)The dimensions of the intake / jackwell can be obtained using BHRA / HIS guidelines. BHRA are given below:

2)Bell mouth dia( D ) = 1.5 d to 1.8 d where d =  column assembly dia

3)Side clearance ( a )= 0.5D to 0.75 D

4)Rear clearance ( b )  = 0.75 D to 1.0 D

5)Bottom Clearance ( C )  =  0.6D to 0.75 D

6)Minimum Submersion ( S )  =  1.5D

7)Distance between pump axis to trashrack shall be 4D to 6D.

8)During detail engineering, the above data shall be furnished by the pump manufacturer.

PRESSURE MAINS:

Pressure mains are most important components and acts as nerves of a L.I. scheme.

While finalizing the pressure mains need to know the following aspects :

1)Importance & Impact of Pressure mains on the scheme.

2)Design considerations of pressure mains.

3)Various types of Pressure mains.

Importance & Impact of Pressure mains on Pumps and cost 

1)Pressure main is the key component in the lift irrigation schemes which work as nerves of the scheme and are very expensive. Whenever length of pressure mains is in kilometers, they take away the lions share of 50 % to 80% of the total cost of the scheme which reflects the importance their design.

2)In view of the huge cost involvement on pressure mains, the type and diameter are to be very carefully designed with cost economics on 2 or 3 alternatives. The type of pipe shall be proposed depending upon the heads, field conditions and longevity.

3)Further, as much as possible / whenever there is feasibility of gravity canal for more than a KM, pressure mains shall be avoided by introducing intermediate pumping station in between duly verifying the cost economics.( Ex : The Chagalnadu LI Scheme ).

Design Considerations Of Pressure mains 

Higher velocity in pipe leads to higher frictional losses results in incresed pump capacity & cost of the scheme.

1)Generally pressure mains are designed for the max. velocity of 2.0 m/s for MS pipes with specifications IS : 2062 and 1.5 m/s for PSC / RCC pipes

2)Velocity upto 4 m/s is also considered in the Steel pipes with specifications IS : 2002 (for Penstock specifications).

3)Similarly lengthy pressure mains increases the total head causing increase in HP of pump further.

4)If the diameter of the pressure main is more than 2.0m, then the fabrication cost of pipe may increase.

5)In view of the above, the number of rows of pressure mains shall be decided duly considering the head involvement, dia and type of material & allowable velocity duly satisfying cost economics.

INFLUENCE OF VELOCITY OF PIPE ON SCHEME

For every 0.50 m/s rise in Velocity of pipe, pumping head rises by 75% to 100% with reduction of dia by 11% to 13%. Hence, it is desirable allow higher velocities in shorter length of pipes and lower velocities in lengthy pipes ( particularly when the length of pipe is in KM ) owing to the recurring power consumption annually ).

ADVANTAGES OF MINIMUM NUMBER OF PIPES

It is been reflected that more number of pipes increases the capital cost along with the pumping head ( i.e., More pipes with smaller dia causes more frictional losses and initial cost as well as recurring power cost over lesser no. of pipes with bigger dia with same velocity 

Thickness of Pipe

The thickness of the pipe shall be determined for the internal fluid pressure as well as for the probable head generated from the water hammer analysis and often head due to water hammer effect will be critical.

1)The head from the water hammer analysis may be approximately 1.5 times total pumping head with provision of pressure relief arrangements and without the arrangements the head may be 10 times of total head, which underline the necessity of the measures to be taken against water hammer effects. Economical design of pipe thickness is must for financial viability of the scheme

2)Thickness of pipe shall also be verified for pipe buried condition with over burden pressure.

3)However, thickness of pipes shall not be less than specified values given in IS 1916 for various diameters of MS pipes.

Conditions of Verification to Buried pipeline

1) Allowable Permissible Stresses & Deflection of MS Pipe :

2) Working Stress for combined bending and direct tensile stress shall not exceed 66 % of yield stress of the material making due allowance for efficiency of welded joint

3) Working Stress for combined bending and direct Compressive stress shall not exceed 50 % of yield stress of the material making due allowance for efficiency of welded joint

4) The allowable deflection of pipe shall not be more than 2% of outer dia of MS shell, for external load & partial vacuum pressure condition and for external pressure and internal pressure condition.

Various Types Of Pressure mains

Concrete Pipes :

1) Pre Stressed Concrete Pipes :

2)Cast Iron Pipes :

3) Steel or MS Pipes :

4) Ductile Iron

5) Bar Wrapped Steel Cylinder Concrete Pressure Pipes

6) Glass Fibre Reinforced Plastic Pipes ( G.R.P. ) Whenever MS pipes with huge heads are to be laid in the ground, they need protection against corrosion by applying epoxy coating or cement mortar on both sides of the pipe, which may escalate the cost of the scheme further as MS pipe itself is uneconomical.

7) Owing to the smoothness and economy over MS pipes, importance of GRP pipes is steadily increasing, but the performance of them for longevity has to be established.

PSC Pipes are Preferable Over MS pipes

1) Cost of 2.50m dia MS pipe with lining & coating is almost 50,000/- per metre length as against 20,000/- for PSC which underlines the cost savings in LI scheme with PSC pipes

2) The apprehension of bursting of pipes is present for the MS pipes also ( It is noticed that MS pipe of Hyderabad water supply from AMRP is frequently getting busted ).

3) Since the danger of pipes bursting is there for both PSC & MS, former is preferable, owing to easy installation and remedial measures in the case of emergency.

4) Generally, there will be movements in the earth fill over a period, which causes the pipe alignment to drift away from the alignment at the joints. However, PSC pipes will be having rubber members in the
joints, which enables the pipe to move slightly and absorb the horizontal deflections any. Where as, MS pipes will be rigid and the joints are susceptible to fail in the above case. To avoid them for MS
pipes, it is desirable to have lap joint between two shells instead of butt joint, which is again un-economical as well as tedious.

Importance Of Surge Protection Devices

1) Design of pipe stability against water hammer / surge is the critical exercise for a LI Scheme and must be done for all the LI schemes, since pipe costs 70% to 80% of scheme cost and failure of pipe at any location causes abrupt halt of the system.

2) Surge analysis / Transient analysis is a very complicated phenomena which needs thorough analysis of the pipe line profile w.r.t. pumping heads to assess the type and number of surge protection devices at appropriate locations. The analysis may be done using a software, exclusively meant for surge analysis, in the absence of which, the scheme functionality may not be assured to its full efficiency.

Water Hammer Conditions

1)High Points in the pumping main alignment

2) Possibility of Water column separation in the main due to sudden power failure

3) Pipe line gradient is steeper than 1 : 20

4) Ratio of frictional loss to working head is less than 0.7

5) Presence of Check valve with slow closing arrangement

6) Velocity of normal flow exceed 1.0 m/

DEVICES FOR CONTROL OF WATER HAMMER

They are required to :

1) Minimize the length of the returning water column causing water hammer

2) Dissipate energy of the water column length by air cushion valve and

3) Provide a quick opening pressure relief valve to relieve any rise in pressures in critical zones.

The above objectives are achieved by the following valves :

Zero Velocity Valve:

When forward vel becomes 25% of the max, the flap starts closing and comes to the fully closed position when the vel becomes zero. Thus, water column on U/S of valve is prevented from acquiring a reversed vel and taking part in creating surge pressures.

Air Cushion Valve :

Allows large quantities of air in the pumping main during separation, entrap the air, compress it with the retuning air column and expel the air under controlled pressure to dissipate the energy of returning water.

Surge Tanks :

Exposed to atmospheric pressure and acts as a balancing tank for the flow variations. Generally placed near the pumping station.

Types Of Pump Houses:

Pump Houses types based on type of pumps are :

1) Wet Pit Pump House

1) Access to pump is not possible

2) Substructure will be always with water for full area

2) Dry Pit Pump House

1) Access to all components of pump is possible

2) Substructure will be always without water and in dry condition

3) In view of the dry condition with access to every component is possible, making maintenance is easy

Types of Pump Houses with its components

SemiUnderground:

•  Approach channel
•  Ramp
• Tunnel Intake
• Tunnel
• Surge pool
• DT Tunnels
• Pump House
• Small Delivery mains
• Cistern

Semi Underground

• Volute Type
• Approach Channel
• Fore bay
• Pump House
• Long Pressure Mains
• Cistern

Design of Pump house

1) Pump house will come exactly on the jackwell for vertical turbine pumps and in the case of centrifugal ( horizontal ) pumps the pump house will be located adjacent nearer to the intake/ sump.

2) Additional bay with sufficient area should be provided connected to the pump house to carry the repairs & maintenance of pumps.

3) Depending upon the site conditions, the control panel bays can be connected to pump house or kept away from it.

4) The platform level of pump house should always be kept 1.0m to 1.50m above HFL / MWL / FRL. The gantry and the roof levels may be kept 8.0m and 11.5m respectively above the platform.

5) In front of pump house, provision for trash rack & gates may be given.

6) Service gate(Stop Logs) for one vent only may be procured wherever independent pump chambers are provided.

7) The platform slab & pump house will be subjected to dynamic loads in addition to static load of pumps when the pumps are in operation.

Various Loads Acting On Pump House

1) Pump & Motor ( Static & Dynamic )

2) E.O.T. & Gantry Crane

3) Control Panels

4) Earth Pressure on 3 sides

5) Water Pressure from inside

6) Self Wt of Structure

7) Other Live Load

Delivery Cister

1) Delivery cistern is required to absorb / dissipate the energy of water falling freely from the pressure mains and delivers into the canals. It shall be designed as vertical drop.

2) The jet projectile length of water fall from the culminating point of the pressure mains shall be calculated and accordingly the length & thickness of the bed required shall be provided to sustain the energy.

3) To have better energy dissipating arrangement, the bed level of the cistern should always be kept below the bed level of the leading canal.

Advantages Of Lesser No. Of Pipes With Bigger Dia:

Ex : Using Hazen William Formula, it is observed that lesser number of pipes with bigger dia gives minimum frictional losses and optimum HP of pump as against more number of pipes with smaller dia, which is illustrated below

i) For 10 Cumecs Discharge for a single row of pipe with Velocity 2.0 m/s, dia of pipe required is 2.523 m for which the frictional loss for 1.0 km length of pipe is 0.89 m. ( i.e., for 10 km , it is 8.90 m )

ii) For 10 Cumecs Discharge for two rows of pipes with Velocity 2.0 m/s, dia of each pipe required is 1.784 m for which the frictional loss for 1.0 km length of pipe is 1.33 m. ( i.e., for 10 km , it is 13.30 m )

iii) For 10 Cumecs Discharge for three rows of pipes with Velocity 2.0 m/s, dia of each pipe required is 1.456 m for which the frictional loss for 1.0 km length of pipe is 1.68 m. ( i.e., for 10 km , it is 16.80 m )

iv) Difference of HP of Pumps for 10 km length of pipes between above i & ii cases is 650 HP, between ii & iii is 525 HP and between i & iii is 1150 HP.

v) Further, lesser no. of pipes results in economy due to requirement for smaller width of trench for laying, land acquisition and CM & CD works.

Importance of Velocity in Pressure main

1) Velocity of pipe does have bearing on the pumping head, functionality of the scheme as well as on the over all cost of the project.

2)he allowable velocity in the PSC pipes is 1.50 m/s and in the MS pipes is 2.0 m/s.

3)higer velocity creates severe water hammer problems

4) Higher velocity increases pumping head abnormally, particularly when the velocity is more than 1.50 m/s

5) Higher velocity necessitates higher thickness of pipes as well as more number of surge protection devices

i) For 10 Cumecs Discharge in a single row of pipe with 3.0m dia, the velocity in the pipe would be 1.4147 m/s for which the frictional loss for 1.0 km length of pipe is 0.38 m. ( i.e., for 10 km , it is 3.10 m ). Quantity of steel for 1Km is 1183 t.

ii) For 10 Cumecs Discharge in two rows of pipes with 2.12m dia, the velocity in the pipe would be 1.416 m/s for which the frictional loss for 1.0 km length of pipe is 0.573 m. ( i.e., for 10 km , it is 5.73 m ). Quantity of steel for 1Km is 1254 t. Lesser dia has more frictional losses and also un-economical compared to higher dia. With the above calculations, it can be inferred that more number of rows increases not only the pipe cost but also the pumping head and in turn pump capacity & running cost of the scheme annually.

Reference Codes / Manuals for L.I.Schemes : (Latest may be referred)

(Latest codes may be referred)

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