How to make them last. - WEAT - North Texas Section | North … · · 2017-07-20To Avoid Cavitation NPSHAvailable>NPSHRequired CENTRIFUGAL PUMPS How they work. ... How they fail

7/20/2017

1

How they work,

How they fail,

How to make them last.

CENTRIFUGAL PUMPS

BY: L. Granger Smith, P.E. ‐ Smith Pump CompanyDr. David Pierce, P.E. – Specific Energy

FOR: W.E.A.T. – North Texas SectionON: Wednesday, July 19, 2017

CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.

INTRODUCTION

WEAT

Optimal pump station management requires correct selection, application, and operation of pumps and motors.

The theory is straightforward and tools exist to help engineers, managers, and operators implement the theory.


INTRODUCTION – Smith Pump Co., Inc.

WEAT

LOCATIONS

Fort Worth

Waco

Austin

Houston

EXCELLENCE

since

1962

Vital Statistics About 70 employees

Headquarters – Waco

Manufacturing – Waco

Warehouse – all four locations

Shop Services – all four locations

Motor Repair/Rewind – Fort Worth shop

Field Services – all four locations


INTRODUCTION – Specific Energy

WEAT

• Est. 2010 in Georgetown, Texas• Principals are from Steger & Bizzell Engineering, est. 1972

• Offerings:• Pump station monitoring

• Pump station optimization

• Lift station control

• And, of course, IIOT


AGENDA

WEAT

• Introduction• Pump and motor basics• Pump hydraulics• Pump station operation• Pump lifecycle management• Efficient operation• Hydraulic transients• Closing


OBJECTIVES (learning)

WEAT

• Proper selection and application of centrifugal pumps

• Proper selection and application of electric motors

• Factors that affect the life of a pumping unit

• Efficient operation of pump stations

7/20/2017

2


PUMP AND MOTOR BASICS

WEAT

• Types of pumps

• Types of motors

• Electric motor characteristics

• Select a motor size

• Motor starting characteristics.



WEAT

VERTICAL TURBINE PUMP

SUBMERSIBLE TURBINE PUMP

DIFFUSER PUMPS

The bowl assembly

• Types of pumpsCLEAR LIQUID PUMPS

VOLUTE PUMPS

Between bearing

Overhung

Horizontal split‐case



WEAT

VERTICAL TURBINE SOLIDS HANDLING PUMP

DIFFUSER PUMP

• Types of pumpsSOLIDS HANDLING PUMPS

For lift stations, these pumps must pass a 2.5” sphere

Dry pit solids handling

Submersible solids handling

Self priming solids handling

VOLUTE PUMPS



WEAT

• Types of pumpsHOW THEY WORK

WEAR RINGAREA, ONE PER SUCTION



WEAT

• Types of motors

OPEN DRIP PROOF

HORIZONTAL GENERAL DUTY

TEFC HORIZONTAL SEVERE DUTY

WP-IVERTICALHOLLOW

SHAFT HIGH

THRUST

VSS TEAAC HIGH THRUST

VSS TEWAC NORMAL THRUST INDUCTION

EXPLOSION PROOF HORIZONTAL



WEAT

• Electric motor characteristics Performance

Motors are generally more efficient at 75% load than at 100% load.

7/20/2017

3



WEAT

• Electric motor characteristics Performance



WEAT

• Electric motor characteristics Performance Selection

RATED C.O.S.Q = 14,757 gpmH = 140 ftE = 86.0%P = 607 hp

ACTUAL C.O.S. FLOWQ = 15,200 gpmH = 140 ftE = 91.0%P = 591 hp

TOLERANCE C.O.S. FLOWQ = 16,000 gpmH = 140 ftE = 86.0%P = 658 hp

700 hp

Sometimes the peak horsepower doesn’t occur at the C.O.S.



WEAT

• Electric motor characteristics Performance Selection Motor starting characteristics

Motor Torque• 100% voltage• 90% voltage• 60% voltage

Pump Torque• Open valve• Closed valve


PUMP HYDRAULICS

WEAT

• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head• Series & parallel operation• Field‐measured curves


PUMP HYDRAULICS

WEAT

• Static headDISCHARGE

PUMP

h = h

static suctionh

SUCTION

total statich

h-

static dischargeh

total static static discharge static suction


PUMP HYDRAULICS

WEAT

• Static head

StaticDischargeHead

Static Suction HeadDatum

Total Head = Static Suction Head+Static Discharge Head

Static

7/20/2017

4


PUMP HYDRAULICS

WEAT

• Static head

System curves are made up of

two fundamentalcomponents ‐ the static

head and the frictional head

120

80

40

0

Hea

d, ft

500040003000200010000Flow rate, gpm

Static Head


PUMP HYDRAULICS

WEAT

• Static head• Friction head

friction

atm

atmos. press.

ASSUME

static suction

total friction

static suction

total static

total headhh

h

PUMP

static discharge

total static ==

hh

hh

+-

frictionh

SUCTION

p

h

atmos. press.

total statichp

DISCHARGE

p

h

atm= p

static discharge

Besides static head we also

have to consider friction and atmospheric

head

• Static head• Friction Head


PUMP HYDRAULICS

WEAT

• Friction Head– HAZEN AND WILLIAMS formula for water

hf = 0.002083 L (100/C)1.85 x gpm1.85 / d4.8655

where: hf = friction head (ft)L = length of pipe (ft)C = Hazen Williams friction factor (60 to 160)

gpm = flow of liquid (gal/min)d = inside diameter of circular pipe (in)

HAZEN AND WILLIAMS formula for waterC = Hazen Williams friction factor (60 to 160)

For “STEEL” pipe the head can vary as follows…EXAMPLES: NEW DESIGN BASIS OLDC Factor 150 130 100 80Multiplier 0.47 0.62 1.00 1.50

Since old pipe friction can be 3 times new

pipe, we must consider both new and old.

• Static head• Friction head• Total Dynamic Head


PUMP HYDRAULICS

WEAT

+ FRICTION LOSSES

+ GAUGE ELEVATIONDISCHARGE HEAD

+ VELOCITY HEAD

TOTAL HEADDYNAMIC

• Static head• Friction Head


PUMP HYDRAULICS

WEAT

System curves are made up of

two fundamentalcomponents ‐ the static

head and the frictional head

120

80

40

0

Hea

d, ft

500040003000200010000Flow rate, gpm

Total

Static Head

Friction


PUMP HYDRAULICS

WEAT

• Static head• Friction head• Total dynamic head• Pump performance curves

7/20/2017

5


WEAT

FLOW

BEP

BEP

HEAD VS CAPACITY

BEP = Best Efficiency Point

TYPICAL PUMP PERFORMANCE CURVE


PUMP HYDRAULICS

WEAT

• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves

TYPICAL PUMP PERFORMANCE

CURVE

Max Impeller

Min Impeller

Rated Impeller

C.O.S.

C.O.S. = Condition Of Service

Brake Horsepower

R.P.M.

C.O.S.

MODEL

M.C.S.F.

NPSHr

A.O.R.P.O.R.


PUMP HYDRAULICS

WEAT

• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head

NPSHr


PUMP HYDRAULICS

WEAT


Net Positive Suction Head (available)

NPSH

NPSHa = hs + hatm– hvp

To Avoid CavitationNPSHAvailable>NPSHRequired


PUMP HYDRAULICS

WEAT




PUMP HYDRAULICS

WEAT



7/20/2017

6


PUMP HYDRAULICS

WEAT

• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head• Series & parallel operation

The Vertical Turbine Pump can be a pump in series.

PUMP

SUCTION PUMP

TWO

SERIESIN

PUMPS

DISCHARGE


PUMP HYDRAULICSWEAT

• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head• Series & parallel operation

DISCHARGE

SUCTION PUMP

PUMPS

PARALLEL

TWO

IN

PUMP

SYSTEM HEAD


PUMP HYDRAULICS – field‐measured curves

WEAT

Severely Worn Factory Condition



WEAT

• Vary the flow (full speed)• Manual

• Adjust with valve

• Vary the speed• Automatic

• Adjust with VFD

• Use affinity laws to estimate full‐speed curves

Per Pump Station:• Suction Pressure or source level• Discharge pressure• Total flow

Per pump:• Power• Speed

LT

OR

PT PT

FT

LT Level Transmitter

Pressure Transmitter

Flow Meter

PT

FT



WEAT

EXAMPLE ‐ Fixed‐speed pump:

Discharge valve varied manually, data collected automatically



WEAT

EXAMPLE ‐ Variable‐speed pump:

Speed varied automatically, data collected automatically

7/20/2017

7


Field‐measured curves ‐ challenges

WEAT

• Power monitoring• Dedicated power meters

• Power from VFDs

• Estimate shaft power

• Flow monitoring• Flow meters notoriously noisy

• Prefer one meter per station

• Data collection• Manual

• Automatic



LT

OR

PT PT

FT



Flow Meter

PT

FT


PUMP STATION OPERATION

WEAT

• Operating range• System curves and operating points• Multiple‐pump parallel operation• Variable speed and system curves• Modeling and design• DEMONSTRATION



WEAT

• Operating rangeP.O.R. – PREFERRED OPERATING RANGE(generally defined by Hydraulic Institute Standards)

Volute Pumps (aka Centrifugal)70 % QBEP 120 %

Diffuser Pumps (aka Turbine)NS 4500 70 % QBEP 120 %NS 4500 80 % QBEP 115 %

• A.O.R. – ALLOWABLE OPERATING RANGE(defined by Pump Manufacturer)



WEAT

• Operating range• System curves and operating points

FLOW

H vs QSYSTEM HEAD

The intersection determines the operating flow of the pump.

PUMP OPERATION


PUMP HYDRAULICS

WEAT

Pumps in parallel

DISCHARGE

SUCTION PUMP

PUMPS

PARALLEL

TWO

IN

PUMP

SYSTEM HEAD

FLOW

3 PUMPS2 PUMPS1 PUMP

• Operating range• System curves and operating points• Multiple‐pump parallel operation

• Operating range• System curves and operating points• Multiple‐pump parallel operation• Variable speed and system curves


PUMP HYDRAULICS

WEAT

200

150

100

50

0

Hea

d, ft

500040003000200010000Flow rate, gpm

7/20/2017

8

WEATCENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.

• Operating range• System curves and operating points• Multiple‐pump parallel operation• Variable speed and system curves

PUMP STATION OPERATIONThis pump curve has it all.


PUMP STATION DESIGN

WEAT

• Step 1: Determine operating range• Range of flows• Corresponding ranges of pressures

• Step 2: Choose number and type of pumps

• Type

• Make & model

• Impeller diameter


PUMP STATION DESIGN – pump selection

WEAT

• Method 1: Identify peak flow and head• Choose pumps to match

• Method 2: Identify second operating point.• Match both operating points

• Method 3: Characterize full range of operating points

• Match all operating points with pump PORs

• Method 4: Model system and demands

• Choose pumps to minimize annual cost


PUMP STATION DESIGN – system definition

WEAT

Many tools exist (including Excel) to compute a range of system curves.



WEAT

The range of system curves for the example system.



WEAT

0

50

100

150

200

250

0 1000 2000 3000 4000 5000 6000

Flow (GPM)

Pump Head (feet)

Empirical operational data characterize desired operating range

7/20/2017

9


PUMP STATION DESIGN – match pumps to system

WEAT

Overlay system curves with pump preferred operating regionsto validate pump selection.


PUMP STATION DESIGN – match pumps to systemWEAT

Detailed model:

• Validate specific operating points

• Limit speeds to stay in POR

• Estimate behavior with worn pumps.


PUMP STATION DESIGN – match pumps to systemWEAT

4 pumps selected for BEP at peak flow

Limit 1 pump to 54% to stay in POR


PUMP STATION DESIGN – optimal pump selection

WEAT


PUMP LIFECYCLE MANAGEMENT

WEAT

• Lifetime pump and motor costs• Pump and motor failures• What makes pumps last• Financial basis for pump repair• DEMO: pumps needing repair


PUMP LIFECYCLE MANAGEMENT – lifetime costs

WEAT

Typical Pump Station: 3 x 200‐hp (room for future 4th pump)

• Capital cost: $ 2M• Capital cost, 3 pumps/motors: $ 200k• Yearly energy cost ($0.10/kWh): $ 100k• PV of energy cost (12 yrs, 3%): $ 1M• PV of 1% savings: $ 10k

• Motor efficiencies: Efficient: 95.0% Premium efficient: 96.2%• Pump efficiencies: 85% to 90%

7/20/2017

10


LIFECYCLE MANAGEMENT – pump & motor failures

WEAT

Pump failures• Seals, bearings, wear rings• Corrosion, de‐alloying• Cavitation erosion• Metal fatigueMotor failures• Seals, bearings• Burnt‐out windings• Loss of insulation

THIS DAMAGE STARTED ON THE

BACK SIDE OF THE VANE.

SUCTION RECIRCULATION



WEAT



WEAT

Pump failures• Seals, bearings, wear rings



WEAT

Pump failures• Seals, bearings, wear rings



WEAT

Pump failures• Seals, bearings, wear rings• Corrosion, de‐alloying• Cavitation erosion• Metal fatigueMotor failures• Seals, bearings• Burnt‐out windings• Loss of insulation

10C temperaturedifference doublesInsulation life

• Bearings• Contamination• Stress & Load• Vibration• Heat• Lubrication

• Windings• Heat• Inverters• Voltage problems• Load• Contamination



WEAT

What fails on a Motor?

7/20/2017

11



WEAT


VFD Spike to windings

Can see 2000V +peaks



WEAT


Good coupling alignment is key to a long run between

failures.



WEAT

Extending pump and motor life – DESIGN

• Adequate NPSH• Design for operation in POR• Design for operation within recommended speeds• Materials selection• Motors on VFDs: mitigate harmonics• HVAC



WEAT

Extending pump and motor life – INSTALLATION

• Alignment• Grouting• Identify resonant frequencies



WEAT

Extending pump and motor life – OPERATION

• Operate pumps within POR, near BEP• Operate pumps with adequate NPSH• Operate within speed limits• Avoid resonant frequencies• Limit stops and starts


LIFECYCLE MANAGEMENT – pump & motor failuresWEAT

Extending pump and motor life – DEMO

7/20/2017

12









WEAT

Extending pump and motor life – MONITORING

• Pump tests: head curve, power curve, pump health index• Vibration monitoring• Temperature monitoring• Seal‐fail detection



WEAT

Good Criteria For Long Pump Runs• Good pump design.• Good foundation and anchoring.• Good piping design.• Good installation.• Good operation.• Operation within the Preferred Operating Range.


LIFECYCLE MGMT – financial basis for pump repair

WEAT

• Test pumps periodically head, efficiency curves

• Estimate 12‐month energy consumption with current pumps

• Estimate 12‐month energy consumption with repaired pumps

• Compute net present value (NPV) for repairs:

Present value of reduced energy

̶ Cost of repair ̶ ̶ ̶ ̶ ̶ ̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶

NPV

• Replace / repair pump(s) when NPV > 0



WEAT

Regional Raw Water Pump Station (rural utility in SE Texas)

Per year: 4B gallons, 6200 MW‐h

Power(hp)

Pump Health Index

700 102%

700 94%

700 94%

700 92%

700 90%

7/20/2017

13



WEAT CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.

EFFICIENT OPERATION

WEAT

• Pump efficiency• Other losses (VFD, motor, friction)• Specific energy: cost per MG• Specific energy vs flow• Required instrumentation• DEMO: optimal pump operation

Remember those wear rings?• Good pump design.


EFFICIENT OPERATION – pump efficiency

WEAT

WEAR RINGAREA, ONE PER SUCTION


EFFICIENT OPERATION – other Losses

WEAT

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pump Station EnergyConsumption

VFD Losses

Motor Losses

Pump Losses

Friction Losses

Useful Work


EFFICIENT OPERATION – minimize specific energy

WEAT

SpecificEnergy

⁄

Energy In (kWh) Work Out (MG)


EFFICIENT OPERATION – the operator’s problem

WEAT

32 combinations2 x 2 x 2 x 2 x 2 =

28 million combinations

31 x 31 x x x >

ON / OFF Control

VFD Speed Control

(0.5 Hz res.)

31 31 31

45 60 45 60 45 60 45 60 45 60

7/20/2017

14


EFFICIENT OPERATION – specific energy vs flow

WEAT

Flow (gpm)

Lower Pumping CostS

peci

fic E

nerg

y (k

Wh/

MG

)

Green: All pumps in POR (1%)Orange: One or more pumps outside POR (99%)

There are 28 million ways to run the pump station.Only one optimally satisfies current demand.



WEAT

Flow (gpm)

Lower Pumping CostS

peci

fic E

nerg

y (k

Wh/

MG

)




WEAT

Flow (gpm)

Lower Pumping CostS

peci

fic E

nerg

y (k

Wh/

MG

)


For example, to achieve 3500 gpm, run Pump 1 at 58.4 Hzand Pump 5 at 55.8 Hz.


EFFICIENT OPERATION – required Instrumentation

WEAT



LT

OR

PT PT

FT



Flow Meter

PT

FT


EFFICIENT OPERATION – demonstrationWEAT CENTRIFUGAL PUMPS

How they work. How they fail. How to make them last.

HYDRAULIC TRANSIENTS

WEAT

• Change in flow change in pressure• Limit transients with pump control valves• Limit transients with VFDs• Other ways to limit transients• DEMO: real pump station

7/20/2017

15


HYDRAULIC TRANSIENTS – the theory

WEAT

Joukowsky (water hammer) equation:

∆ ∆

Where:∆ changeinhead ft∆ changeinvelocity ft/s

wavespeed ft/sgravitationalacc. 32ft/s2

Wave speed: 1200 to 3800 ft/s depending on pipe material.

5 ft/s velocity; ductile iron pipe, sudden loss of power.∆ 5ft/s

3800ft/s

∆ 5 ·380032.2

ft

∆ 590ft 256psi

PVC pipe: 1200ft/s; ∆ 186ft 81psi

Without mitigation, pressure zero, creating vapor pocket.


HYDRAULIC TRANSIENTS – example

WEAT

Transient reduced by reflections if:

shut downperiod pipelengthwavespeed

Use PCV or VFD to limit transients.


HYDRAULIC TRANSIENTS – importance of pipe length

WEAT CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.

HYDRAULIC TRANSIENTS – pump control valves

WEAT

Traditional solution: PCV limits ∆ during starts, stops.

Issues:• Flow through PCV is nonlinear• Delay often too short to be effective• PCVs are high‐maintenance


HYDRAULIC TRANSIENTS – variable frequency drives

WEAT

Simple solution: long ramp rates (acc., dec. settings)

Problems: flow is nonlinear; delay often still too short

Better solution:

• Monitor pressure• Limit flow change based on pressure

(until mitigated by reflections)


HYDRAULIC TRANSIENTS – worst case: power loss

WEAT

Solutions for power loss (PCVs and VFDs ineffective):

• Surge pressure tank• Pressure relief valve• Air‐release / vacuum‐breaker valves

Pressure‐based VFD control still neededfor normal operations.

DEMONSTRATION: VFD w. & w/o control; PRV

7/20/2017

16


CLOSING

WEAT

Optimal pump station management requires correct selection, application, and operation of pumps and motors.

The theory is straightforward and tools exist to help engineers, managers, and operators implement the theory.

Thank you!

Documents

How to make them last. - WEAT - North Texas Section | North … · · 2017-07-20To Avoid Cavitation NPSHAvailable>NPSHRequired CENTRIFUGAL PUMPS How they work. ... How they fail