IS 15310:2003

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Indian Standard

EIYDRAULJC DESIGN OF PUMP SUMPS ANDINTAKES — GUIDELINES

lCS 93.160

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

F’ebruaq 2003 Price Group 4

Intake Structures Sectional Committee, WRD 11

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, atler the drafi finalized by the Intake StructuresSectional Committee had been approved by the Water Resources Division Council.

Performance of pump is influenced to a considerable extent by the flow conditions at the intake. Swirls and airentraining vortices affect pump performance, causing considerable noise, vibration, cavitation damage, increasedsuet ion losses and reduction in efficiency. Large flow swirl intensities “increasethe frictional losses which reducethe available net positive suction head @PSH) of the pumps. The swirls can also cause pre-rotation at the impellerinlet, particularly in the case of vertical turbine pumps where impeller is very near to the sump bottom, it may leadto shock losses at the entry resulting in tht pump operating at off-duty point affecting the cavitation characteristicsof the pump. Site constraints also have significant effect on the configuration.

Proper pump intake design takes care of problems referred above. Though pump sump and intake are designed asper general guidelines actual design and measures for its smooth functioning are finalized through model studies.

The composition of the committee responsible for formulation of this standard is given in Annex A.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value,observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with1S2:1960 ‘Rules for rounding off numerical values (revised)’. The number of significant places retained in therounded off value should be the same as that of the specified value in this standard.

1S 15310:2003

Indian Standard

HYDRAULIC DESIGN OF PUMP SUMPS ANDINTAKES — GUIDELINES

1 SCOPE

This standard stipulates the guidelines for initialhydraulic design of pump sump and intake structuresfrom approach channel up to its entry into suction pipeof the pump.

2 DEFINITIONS

2.1 Pump Sump

A lined excavation generally of a simple geometricshape adjacent to the pump intake. When the intake isdirectly adjacent to a river or reservoir, the areaimmediately upstream of the intake section is termed‘forebay’ (see Fig. 1).

2.2 Pump Intake

The structure between the pump sump or forebay andthe pump itself is termed as pump intakes. Generallypump intake is in the form of bell mouth, suction bowland column pipeline. The intake can be horizontal orvertical or inclined. In some cases, the intake is part ofpump itself(see Fig. 1).

2.3 Pumpbays

In case of multiple pump installations the pumps areusually separated from each other by separating walls(piers). Individual pump chamber is then called aspumpbay.

2.4 Dimple Vortex

A free surface vortex making a dimple on the freesurface without air entrainment (see Fig. 2 a).

2.5 Air Entraining Vortex

A vortex which enters an intake from the free surfacewith intermittent or continuous air entrainment(see Fig. 2 b).

2.6 Submerged Vortex (Swirl)

A vortex which enters the intake from a solid flowboundary with submerged vapour core (see Fig. 2 c).

2.7 Swirling Flow

Flow usually caused by large scale rotation in the bulkof the fluid in the sump which is then amplified as theflow converges into the intake.

FREE SURFACE FLOW

Y7

DISCHARGE#

.— —— .— —.—— —— —— ___——— —— —. o

—— — J.— ——SUMP _– —.—”

(INTAKE

(A)

fLINTERNA~ FLOW

ELEVATION

PUMP —- —---~

(B) PLAN

FIG. 1 DEFINITIONSKETCHFORPUMP,SUMPANDINTAKE

1

IS 15310:2003

2.8 Critical Submergence

2.8.1 Critical Submergence for Horizontal Intakes

It is the minimum vertical depth from the surface ofwater in the pump sump to the top most point of intakerequired to prevent air entraining vortices (see Fig. 3).

2.8.2 Critical Submergence for Vertical Intakes

It is the minimum depth from the water surface to thepump intake to prevent entry of air and formation ofvortices as indicated in Fig. 4.

2.9 Minimum Submergence

The depth of submergence over a be]lmouth at theallowable lowest water level.

-TM75

(a) DIMPLE VORTEX

MIN. WATER LEVEL

2.10 Swirl Angle

The swirl angle is defined as

O= arctan+a

where

Vt= tangential velocity component of swirling flow;and

V,= axial velocity component of flow in pipeline.This is used to measure intensity of swirling flowin the pump intake.

2.11 Net Positive Suction Head (NPSH)

Net positive suction head (NPSH) is the total inlethead

-3!Jlj--’(c) SUBM:SRIJE&VORTEX

J[b) AIR ENTRAINING

VORTEX

FIG. 2 VORTEXCLASSIFICATION

n,.DRY WELL

W=2D -— M TO PUMP

/

MIN WATER LEVEL

*

.—.S=l-S OIMIN “

1

0 ~ x=o/;c =0/2

/ /’//////////

W*2O

[A) HORIZONTAL INTAKE (B) TURNED 00WN .8 EL LMOUTH

FIG. 3 SUMPDESIGNFORSINGLEPUMPDRY WELL SUMP

2

plus the head corresponding to me atmosphericpressure, minus head corresponding to the vapourpressure:

P. P“NPSH = H+ ——

P, P,

where

H = total inlet head in cm,

PO= atmospheric pressure in g/cm2,

IS 15310:2003

P,= vapour pressure in glcmz,.and

/2, = density of water in g/cm3.

NOTES

1. NPSH and inlet head are measured/taken from a referenceplane (Fig. 5,).

2. The inlet head used includes velocity head based upon theaverage inlet velocity.

3. Reference.plane is the horizontal plane through the centerof the circle formed by the external points of the impellerblades (see tig.5).

I I ‘OTORM

Ei-i!17,—.VALVE >

(A)wET WELL

dc

FIG. 4

(B) ORY WELL H0R120N- (C)DRY WELL-TAL FLOW iNTAKE TURNED-OOWN INTAKE

: Critcal Submergence Depth

WET AND DRY PUMP INSTALLATION

& I

H=

P,, =

p,=

P,, =

h, =

vertical height of the water surface in the sump above the datum. Thus if the water surfaceis below the datum, ‘H’ is a negative quantity;

atmospheric pressure, g/cm2;

density of water;

water vapour pressure; and

head loss in suction pipeline cm.

FIG. 5 DMGRAMTO ILLUSTRATE‘NPSH’

3

IS 1S310 :2003

3 TYPES OF PUMP INTAKES

The position and location of pump intake generallydepends upon the source of water available for pumpingand the proximity of the plant to the source of water.The pump intakes may be broadly classified as :

a) pump intakes placed in source of water, and

b) pump intakes placed away tlom source of water.

4 STANDARD DESIGN

4.0 General

Standard design of sump mainly depends upon ratedflow per pump to be handled for irrigation, power plant,industrial project, sewerage system, etc. This will inturn govern the type and number of pumps required.

The following aspects shall be considered for a goodsump design:

a)

b)

c)

d)

e)

Even flow distribution;

Ideal flow condition in each pump bay withrespect to swirl and vortex formation andprevention of pre-rmtation;

Independent pump operation;

Use of screens in pump bays for arresting alltrash and floating material; and

Provision of gates to isolate pump bay formaintenance, etc.

For satisfactory pump operation the flow into suctionpipe intake has to be evenly distributed across the areaand this can be achieved by proper design of sumpcomponents. Sharp corners, abrupt turns and nonsymmetry should be avoided.

While designing the sump, prevention of eddies andvortices in the channel and pump bays-and the conditionof the flow approaching inlet of bell is important.

4.1 Single Pump Sumps

A pump can be installed in a wet or a dry well. Avertical turbine pump suspended in a wet well and asimilar pump in a dry well is shown in Fig. 4. In a drywell the bellmouth maybe directed in the back wall orturned down through an angle of upto 90° as shown.

4.1.1 Vertical Entty Pumps

4.1.1.1 Figure 4 shows basic design for wet well sumpfor a vertical pump. All the dimensions are given interms of bell mouth diameter (D), which is generallytaken as 1-5 to 1.8 times pump column pipe diameter.

4.1.1.2 Side wall clearance

The clearance between side wall and bellmouth shallbe maintained between D/3 and D/2.

4.1.1.3 The bottom clearance (C) between bellmouthand sump floor shall be kept not less than D/2.

4.1.1.4 Backwall clearance (B) between bellmouth andbackwall shall be D/4 to D/3 (Fig. 6a).

4.1.1.5 The upstream flow distribution sha}lbe uniformwithin a distance at 3 D from pump centerline(Fig. 6c).

4.1.1.6 The sharp corner shall be avoided or shall beeither blanked or given fillet of radius as shown inFig. 6a, 6b and 6c.

4.1.1.7 Width

Width of the pump bay shall be minimum 2 D.

4.1.2 Horizontal Entry Pumps

4.1.2.1 Figure 3 and Fig. 4b show the general layoutfor dry well sump with a horizontal entry to the pump.This configuration is usually adopted when reliabilityis the prime requirement, since the pump is accessibleat all times for maintenance. All the dimension are givenin terms of bell mouth diameter(D), which is generallytaken as 1.5 to 1.8 times pump column pipe diameter(d).

4.1.2.2 Channel width

The channel width shall be 2D (same as in the case ofvertical entry pumps)

4.1.2.3 Bottom c[earance

Clearance from bottom (C) for turned down elbowarrangement shall be kept D/2.

4.1.2.4 Clearance with backwall (B) shall be D/4 toD/3 (same as in the case of vertical entry pumps).

4.-1.2.5Minimum water level (MWL)

The minimum water level is decided by external factorssuch as level of the incoming pipe culvert, NPSHrequirements of the pump, etc. Considering thesefactors, water level should be kept as low as possible toreduce the cost of civil engineering works.

Minimum water level = C + S + safety margin

where

C = bottom clearance between sump floor and bellmouth (C= D/2)

S= submergence ( S >1.5 D)

4.1.2.6 Straight length of approach channel in pumpbay shall be upto 10 D downstream of majorobstructions to flow path (for example, gate,structure,bridge piers, etc) for example, screen. However, modeltests are advisable for determining the exact length ofapproach channel (see Fig.7 for details).

4.2 Multiple Pump Sumps

Wet well pumps are the commonly used pump inmultiple pumps sumps.

4

IS 15310:2003

(0) ‘/2+4 ‘SIDE WALLcLEAff”NcE

OR{D/3TD (2/21

x RADIUS-D/~

WIDTH=2D

D

(b)

ORJ b~

4 I--%

PLANE OF+r-1UNIFORMFLOW

-t!\s=l ~/20 (MINI

L!1-o--1

33E!Ir-

RAOIUSROJ

C=BOTLDM CLEARANCEI c>o/2 )

UNIFORM (d)FLOW

o

&’o+

FIG.6 SUMPDESIGNFORSINGLEPUMPWET WELL SUMP

OBSTR

MAJOR

UCTIONS TO FLOW SUMP FLOOR TO BE LEVEL

FOR THIS LENGTH

AREA RATlO @A=OC5/

1- L =10 O

!3LJMp FLOOR TO BE LEVELFOR THIS LEVEL

FIG. 7 LENGTHOFAPPROACHCHANNEL

5

IS 15310:2003

4.2.1 Wet Well Pump Iwtallation

Figure 8 shows alternate ways of installing pumps in asump. The arrangement shown in Fig. 8a is used whereuniform steady flow occurs just upstream of the intakes.However, if the approach flow is less uniform than ideal,the arrangement shown in Fig. 8b is preferred.

4.2.1.1 Width ofpump house

The width of pumpbay is kept minimum 2 D. In caseof open sump the minimum width of pump house is2ND and in case of unitised-pump it is 2 ND+(N– I)Twhere N is number of pumps and ‘T’ is pier wallthickness between two pumps.

4.2.1.2 Center to center distance between pumps shallbe kept minimum of 2D for open sump and 2.D + T forunitized sump to provide adequate clearance inpumpbay.

PLANE OF UNIFORM FLOW !

(a) OPEN SUMP

4.2.1 .3Tump inlet velocity in column pipe is generallylimited to 3 m/s and velocity at entry of bell mouthshall not exceed 1.3 m/s.

4.2.1.4 Approaches to the sump are shown in Fig.7 foropen and unitised sump. Velocity of the flow of achannel conveying water to sump should not be greaterthan 1.2 m/s.

4.2.1.5 Piers

In the case of multiple pump arrangements, the piersare erected between two pumps to avoid interferenceof one pump on the other and to cater for structuralrequirements of pump house. As a thumb rule, thelength of piers can be taken as 10 D where D isbellmouth diameter. The nose of the pier should besmooth, preferably semicircular. Piers also help instraightening the flow approaching pump bell.

I +2’+1I

+IV , 60+2T

-kYu

tl

d

TOP OF PIER WALLABOVE MAX. WATER LEVEL

l-l

(b) UNITISEO SUMP

IL

SS1.5 D 1(tJwlIII

1 I )I ‘ f

‘/20

FIG. 8 BASIC SUMPDESIGNSFORMULTIPLEPUMPSWET WELL ARRANGEMENT

6

IS 15310:2003

4.2.1.6 Themaximum divergence fortheforebay sidewalls with respect to forebay center line should belimited to 20 degrees and the maximum slope at bottomto be not more than 10 degrees to avoid separation offlow. The velocity in the pump bays should not bemore than 0.3 m/s.

4.2.1.7 Screens should be provided at the inlet of eachpump bay in order to arrest all trash and floatingmaterial and straighten the flow.

5 MODEL STUDY

To finalize a pump sump and intake design for anyapplication, hydraulic model studies on a geometricallysimilar model are advisable to study flow conditions,cavitation, vortex formation, efficacy of antivortexdevices, etc. However, to make minimum alterationsin the model during experimental studies to achievesatisfactory flow conditions, it is essential to haveinitial ly some intake design for that application basedon some guidelines/thumb rules, according to which amodel can be constructed for initial studies.

5.1 As a thumb rule the capacity of the sump may bebased on the detention period. A detention period of 7to 10 minutes depending on the rate of flow of a singlepump or multiple pumps maybe a reasonable value.

6 ANTI-VORTEXBWIRL DEVICES

Various expedients (anti-vortex/anti-swirl devices) needto be evolved first with Freudian velocity through intakeif the flow conditions are observed with occurrence ofswirls and vortices. The efforts should be made tominimise pre-rotation.

The type of expedients generally adopted are flow guidebaffle wall, breast walls, floating rat%, grid walls, anti-swirl cones, splitter vanes, etc. However, the mostsuitable or optimum suitable device can be finalisedthrough trial runs on the model and the solution mayvary from case to case.

The effectiveness of the anti-vortex device shall beverified for flow velocities higher than Freudian, andupto the actual velocity, that is, prototype velocity, asmay be considered necessary.

7

1S 15310:2003

ANNEX A

(f’cv-ewm-d)COMMITTEE COMPOSITION

Intake Structures Sectional Committee, WRD 11

Organization

Central Water Commission, New DelhiIlharat Heavy Electrical Ltd, New Delhi

Central Board of Irrigation and Power, New Delhi

Central Design Organization, Nasik

Central Electricity Authority, New Delhi

Central Inland Capture Fisheries Research Institute, Kolkata

Central Water Commission, New Delhi

Central Water and Power Research Station, New Delhi

Consulting Engineering Services (India) Ltd, New Delhi

Indian Pump Manufacturers Association, Mumbai

Irrigation Department, Government of Punjab, Punjab

Irrigation Design Organization and Research Institute, Roorkee

National Hydroelectric Power Corporation Ltd, Faridabad, Haryana

Narmada Water Resources and Water Supply Department, Gujarat

Public Works Department, Govt Of Tamil Nadu, Tamil Nadu

Tehri Hydro Development Corporation Ltd , RkhikeshBIS Directorate General

Representative(s)

StrRJK, S. BnAnA(Chairman)

SHRJB. SENGUPTA

SHIU P. SINHA (Alternate)DR A. S. CHAWLA

SHRI A. N. BHARGAVA(Alternate)SUPERINTENDINGENGINEER(G. O.)

-SUPERINTENDINGENGINEER(GATES) (Alternate)

SHRJA. K. JAIN

StrRINEERAI KUMAR (Alternate)

DR MANJRANIANSINHA

SHRJV. V. SUGONAN(Alternate)DIRECTOR(NSH)

DIRECTOR(SSPH) (Alternate)SHRJS. R. BHAMBURE

SHRI B. S. KOLKARNI(Alternate)SHRI V, K. KAPUR

SHRJP. K. SANGHI(Alternafe)SHIOs. L. ABHVANKAR

SHRI R. G. PADALKAR(Alternate)CHIEFENGINEER(RSDD)

DIRECTOR(T&P) (RSDD) (Alternate)

CHIEF ENGINEER(PHD)SUPERINTENDINGENGINEER(Alternate)

SHRJV. K. KAPOOR

SHRI A. K. JAIN (Alternate)OFFICERON SPECIALDOTV ( 1)

UNDER SECRETARY(WJm) (Alternate)

SHRJM. DURAIRAJ

SHRI T. KRISHNASWAMY(Alternate)SHRJSHAILENORASINGH

SHRJS. S. SEf’1%,Director and Head (WRD)[Representing Director General (Ex-oflcio)]

Member Secretary

SHRJMATJROSYDSSAWAN

Joint Dkector (WRD), BIS

8

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Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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