2 final pumps and pumping stations

7/28/2019 2 Final Pumps and Pumping Stations

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Pumps and Pumping Stations

Presented byNed W. Paschke, PE

University of Wisconsin-Madison



Outline of this Session

1. Pump Types and Features

2. Estimating Flows and Differential Heads3. Pump Performance Curves and System Curves

4. Types of Pumping Stations

5. Wet-wells, Sumps, Suction Chambers

6. Piping, Valves, Screens, and Other Features

Pumps and Pumping Stations



1. Pump Types and Features

A. Centrifugal End-SuctionЦентробежные насосы с односторонним всасыванием

Installed in a dry pump room

Horizontal or vertical shaft

Volute elevation is below water surface

Impeller is outside of bearings

Stress on shaft, due to impeller

Wide performance selection available



B. Centrifugal Double-Suction, Split CaseЦентробежный насос с двухсторонним всасыванием и разделителем

Usually horizontal, but can be vertical

Installed in a dry pump room

Impeller is supported between the bearings, symmetrical.

Flow splits and enters impeller from both sides.

High efficiencies available. For clean water, not solids handling.



C. Submersible Motor is integrally sealed to pump. Always vertical.

Pump + motor operates submerged in the sump or reservoir

Advantage: small footprint, no separate pump room needed.

A popular, growing trend especially for small - medium size facilities



D. Vertical Turbine Pumps

Вертикальный турбонасос Ideal for groundwater wells.

Or can be mounted above reservoirs and sumps

Motor above, pump below.

Small footprint area. Saves space.

A series of impellers, directly in series.

Can develop high differential heads.



E. Archimedes Screw Pumps Винтовые насосы Probably the oldest type of pump (circa 250 BCE)

Handles a variety of flow rates at constant speed

Can be open or closed design.

Non-clogging, good at solids handling.



F. Progressing Cavity Pumps Поступательный кавитационный насос

For handling viscous sludges,difficult fluids, high solids.

A “positive displacement” pump,flow not affected by head.

More expensive, lower efficiencies than centrifugalpumps.

High wear, stator replacements.Low speeds are best.



G. Other Special Purpose Pumps

Self-priming,suction-lift pump.Mounted abovewater level

Самозаполняющийся насос

Recessed impeller vortexpump, for solids and rags

Вихревой насос

Chopper pump,with cutter blades

Насос с измельчителем

…and many

others!



10

Looking for a Centrifugal Pump?

1. Manufacturer with a strong experience record2. Good operating performance at desired flows & heads

3. High efficiency - saves energy and reduces wear

4. Solids handling capacity - to pass at least a 75mmsphere (but this will reduce efficiency somewhat)

5. Low-speed rpm preferable to high-speed rpm. Lesswear. High-speed is smaller and less costly, though.

6. Minimal shaft deflection (less than .05mm is good)

7. Inspection/ cleanout ports at suction & discharge

8. Nominal pump “size” = connection size at discharge(note: suction diameter is often larger)

9. Compare bare pump weights - heavy is good



11

N. Paschke 2011

Bearings

Key Pump Components

Wear rings

Mech. seals

or packing

Casing (volute) Impeller

SuctionShaft

Discharge



2. Estimating Flows & Differential Heads

Note: Use actual

local flow data if

possible. Flows

can vary greatly

between differentregions and cities.

Let’s Start

with Typical

Average

Flow Rates

Trend: Water

use per person

is declining in

the US.



Flowrate Variation – an Important Aspect

A Wastewater Pumping Example

Selecting a peak design flow:

• Not an easy decision.• Involves both engineering and policy.

• It greatly affects the remaining design.



Selecting Peak Design Flows

Facilities must handle a wide range of flows: Time-of-day, present vs. future, dry-weather vs. wet

Wastewater peaks: governed by wet weather events.

Drinking water peaks: governed by dry weather demands,fire flow requirements, and storage availability.

Selecting the “Peak” Flow. Different methods are in use:

Peak/average ratios (often 2.5 to 5, sometimes more)

Historical experience & probability analysis

Dynamic computer modeling, incl. storage & travel times

Note: Define the duration and frequency of the “peak”

Final design requires both engineering and policy:

How big is big enough? How much can we afford?

14



DISHARGE VALVE &FITTING LOSSES

SLOPE OF PIPE

FRICTION LOSS

EXITLOSS

Hp

Note: There are 3 Components of Pumping Head

STATIC

HEAD

Differential Pumping Head and its Components

N. Paschke, Univ. of Wisconsin-Madison 2011



Estimating Pipe Friction Losses

(each formula has its own empirical “roughness” factor)

where R = hydraulicradius=

area

wetter perimeter

=

p r 2

2p r =

r

2for circular pipes flowing full

Hazen –

Williams (metric units)

Darcy - Weisbach

54.063.0849.0 S RC V

L RC

V Lossor

85.1

63.0849.0

Common C values in

pipes:

Loss= f L

D

V 2

2g

L = pipe length

D = pipe inside diameter

V = velocity = Q/A = flowrate / pipe

area g =

gravity = 32.2 ft/s2 =9.81m/s2

f = friction factor from Moody diagram

where

where S = friction slope = Loss /Length

150 “smoother

100 “rougher ”

See tables for

typical pipe

roughness values

Friction Losses are proportional to V2 or V1.85



static head

valve & fitting losses

pipe friction losses

Components of

the system curve:

shut-off

head

operating point

static head

17N. Paschke 2011

3. Pump Performance Curves andaaSystem Curves

Flow rate (gal/min) (1 gal/min = 3.785 liters/min)

P u m p i n

g h e a d ( f e e t )

( 1 f t . = 0 . 3

0 4 8

m )



Sensitivity to Static Head Ranges

Pump operating range

What are some examples of a

changing static head?

18N. Paschke 2011

P u m p i n g h e a d ( f e e t ) ( 1 f t . = 0 . 3

0 4 8

m )




Sensitivity to Static and Friction Ranges

Possible pump operating range

19

Old pipes can become more

rough, due to pipe corrosion,and interior deposits.

N. Paschke 2011

P u m p i n g

h e a d ( f e e t ) (

1 f t . = 0 . 3

0 4 8 m )




Sensitivity to Pump Wear

Possible pump operating range

20

original new pump curve

pump is badly worn

How would we know if our

pump is wearing?

N. Paschke 2011

P u m p i n g h e a d ( f e e t ) ( 1 f t . = 0 . 3

0 4 8

m )




2 pumps in series

2 pumps in parallel

1 pump

Series and Parallel Pumping

System curve

add pump curves horizontally

add pump curves vertically


P u m p i n g

h e a d ( f e e t ) (

1 f t . = 0 . 3

0 4 8 m )



☐ Size ☐ Speed ☐ Flow ☐ Head ☐ Impeller ☐ Vanes

☐ Efficiency ☐ Max. Solids ☐ Power required ☐ NPSHR

Pump Performance Curve: Lots of Info.= 150mm



Net Positive Suction

Head Available (NPSHA)

EXAMPLE. Estimate the NPSHA, Given Elev. 1 = 100 m., Elev. 2 = 98 m,

Estimated suction losses = 1m, Temp = 100 C, Elev. = sea level.

NPSHA = 10.3 m + (100 m – 98 m) – 1 m losses – 0.12 m vapor = 11.2 m

Note: NPSH problems use absolute

pressure, not “ gage” pressure

NPSHA is aproperty of the

system, not the

pump.

It indicates the netabsolute head

available at the

suction side of the

pump impeller,point 2 .

NPSHA = Ha + (Z1 – Z2 ) – Losses 1-2 – Hv

Ha = atmospheric pressure head

= 10.3 m at sea level

= 8.6 m at elevation 1500 m

Hv = vapor pressure (absolute)

0.12 m at 10o C

0.24 m at 21o C

TYPES OF STATIONS



TYPES OF STATIONS

SUBMERSIBLE STATION DRY-WELL STATION

“Dry-well Stations” Also called “dry-pit” or

“conventional”

Pump room (or dry well) housesthe pumps

Separate chamber (wet-well, or sump) stores incoming wastewater

“Submersible Stations” Pumps/motors are submerged

within the wet well

No separate pump room exists

Uses separate valve vault and

control room 24

4. Types of Pumping Stations



25

Advantages of

Dry-well Stations:

A long experience record A wide selection of pumps

Easy access to pumps

Visual, hands-on inspection

Chosen for most large stations

Advantages of

Submersible Stations:

Lower cost, no dry well

Less piping & valves

Frequent access not needed

Technology has improved

Valves accessible in vault



Examples of Pump Rooms in Dry-well Stations



Down in a

Pump Room

Inside a Control Room on

the ground floor

27



Examples of Pumping Station Exteriors



29

A Large Dry-well Station in Profile



30

Same Station in Plan View



31

Starting an excavation

Dewatering

the site



Constructing the

base slab

Constructing

the walls32



33

A large booster station

in Virginia

Location: Kempsville Pressure

Reducing Station, Hampton Roads

Sanitation District, Virginia



34

A deep lift station in Arizona

Location: City of Glendale, AZ

Submersible pumps

installed in dry-well station.Variable frequency drives,

emergency generator on

grade floor, odor control,

architectural design.



35

A large circular

submersible station in Texas



36

On the surfacedeck

Location: Houston, Texas

In the

dischargechamber



A small, factory-built

submersible station



38

A factory-built steel dry-well station

Two pumps (duplex)are most common

Usually circular shape

Typical diameters:8-ft. to 12-ft.

Oval or peanutshapes for three or more pumps

Plus pre-castconcrete wet-well onfield-poured base slab



Example of a factory-built steel station



40

A self-priming

suction-lift station

Pumps mounted above the water

surface level

Pump must include self-priming

vacuum-break, to “lift” water intoimpeller

Easy pump access, close to surface

Low cost station

But may be less reliable



5. Choosing the Size and Number of Pumps

Pumping stations must handle a wide range of flows. Minimum, average, peak. Present vs. future.

Objectives:

Must be large enough to handle the peak

Must be reliable and efficient for normal daily operation

Overlapping Considerations

How many total pumps? Variable-speed or constant?

How to handle the peak? Parallel pumping?

Future expansions?



Selecting a Team of Pumps

A Two-pump Constant-speed Station? Common approach for smaller stations

Each unit is sized for peak. Lots of cycling. High energy use.

A Three-pump (or more) Constant-speed Station?

Various combinations of sizes and/or parallel pumping

Allows smaller, medium pump(s) for typical daily flow.

Fewer cycles. Can save energy.

A Variable-Speed Station?

Can provide flow flexibility with fewer total pumps

But must account for variable pump efficiencies and VFD losses

Is Storage Available, to Reduce the Pump Range?

P C li E l for a mid sized



Example: two equal pumps,constant-speed, peak capacity

Example: multi pump (3 or more)

graduated-capacity, constant

speed system. Small unit sized

for 2 ft./sec.

Pump Cycling Examples for a mid-sizedwastewater station

Flat system curve example:



Parallel pumping

is most useful

when system head

curve is fairly flat.

at syste cu e e a p e

One pump = 16,000 gpm

Two pumps = 30,000 gpm

Steep system curve example:

One pump = 16,000 gpm

Two pumps = 18,000 gpm



Variable-speed Pumping Example


P u m p i n

g h e a d ( f e e t )

( 1 f t . = 0 . 3

0 4 8

m )



Pros of Variable –Speed

Inflow = Outflow. Allowssmaller storage.

Provides smoother dischargeto downstream process

Fewer starts and stops.

Saves mechanical wear andreduces water-hammer

Some energy savings, if system head-loss is large

Can satisfy flow range withfewer total pumps.

Cons of Variable –Speed

Equipment is more costly.

More complex. It could fail.

Useful lifespan is more limited(10-15 years)

Some extra energy losses withinequipment

Additional space needed incontrol room

46

Variable-Frequency Drives, Pros and Cons



6. Suction Chambers (Wet-wells, Sumps)

Suction Chambers Serve Multiple Purposes:Providing a storage volume

Inflow rate is different than outflow rate (pump discharge)

Electric motors have limited allowable starts per hour

Example: Maximum 6 starts/hour = Minimum 10 minute cycle time

Protecting against swirls, vortices, air entrainment

These can disrupt the pump performance

Avoiding solids’ deposition

To reduce problems with cleaning, odors, and corrosion



Examples of small circular designs

48Separate dry-well type Submersible

Suction Chambers



Source: Flygt ITT pump

Suction Chambers

with Baffles

(to reduce swirls

and vortices)

Submersible

Separate

dry well.



Selecting Depths, Volumes, & Cycle Times

for Suction Chambers

1. Establish allowable hi-water elevation

2. Compute required live storagevolume*

3. Provide submergence to preventvortices in pool

4. Allow clearance below suctionflare for entry

5. Check that volute remainsflooded

AlloweTimeCycleQump P 41

*for single step ON-OFF stations



51

Flared Suction Entrance Pipe in Suction

Chamber



Submergence depths for pump inlet,

to prevent swirls and vortices.

Source: Flygt ITT pumps

Examples

“Self-Cleaning” Trench Suction Chamber



Self Cleaning Trench Suction Chamber

5 Pi i V l S Oth F t



5. Piping, Valves, Screens, Other Features

Ductile iron PVC

Common Materials for Underground Piping



55

Common Materials for Underground Piping

Ductile Iron

A standard product, AWWA C150, C151

Push-on gasket joints

6 meter lengths

Up to 50 deflection

Same o.d. for allthickness classes

Poly wrap for corrosion protection

Reinforced Concrete Pressure Pipe (RCPP)

Custom built for your pressure & cover depth

Steel wire for strength + steel cylinder for watertightness

Available in very large sizes. ( > 4 m dia. available)

Plastics: PVC, HDPE, Fiberglass

Excellent corrosion resistance

Pressure ratings good, but lessthan ductile or steel

Cracking? PVC may crackwhen coring holes under load

Flexible pipe depends on soil toprevent deflection

good bedding + compactionneeded

Types of Isolation Valves



56

Eccentric Plug Valve

Resilient Seated Gate Valve

Types of Isolation Valves



57

Check Valve, with Oil Cushion Chamber

600mm

Combination Air Valves



Combination Air Valves

58

ARI type VENT-O-MAT type

Installed at high points in pipeline

To release air trapped in pipeline Also to admit air into pipeline to relieve vacuums



E P & B k O ti



60

Emergency Power & Backup Options

1. Connect station to two

independent electric power feeds2. Provide onsite generator in auto

standby

3. Provide portable generator to

connect outside of station4. Provide onsite diesel or gas-

driven pumps, capable of peak

flow

5. Provide portable pumping units

(and connections) capable of

peak flow, or

6. Holding facility for

24-hours storage



Summary: Pumps and Pumping Stations

Many different pumps to choose from

Submersible or dry-well

Centrifugal, vertical turbine, Archimedes, positive displacement

Pump performance characteristics

Flow, head, efficiencies, speed

NPSH, solids handling, power required

Choosing a set of pumps

Size and number, individual, parallel, or series

Constant speed or variable speed

Station types, sump geometry, other features

Submersible, dry-well, sump sizes, baffles

Valves, screens, emergency power

Questions, Discussion?



Questions, Discussion?

Thank You!

Ned W. Paschke, PE

Univ. of Wisconsin-Madison

432 N. Lake Street

Madison, WI USA 53706 608-263-4705

[email protected]

2 final pumps and pumping stations

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