chapter 6 : pumps

ME444 ENGINEERING PIPING SYSTEM DESIGN

CHAPTER 6 : PUMPS

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LAST SESSION1. PIPING SYSTEM DESIGN PROCEDURE2. PIPE THICKNESS3. PIPE SIZING AND SYSTEM PRESSURE

DROP

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CONTENTS1. Fundamental of Pumps2. Operating Point3. Pump Selection4. Pump Installation

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1. Fundamental of Pumps

When source pressure is not enough to provide desired output, pump is utilized.

SOURCE PIPING SYSTEM END USERS

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Pump output

Flow rate and Pressure rise.

pQE fluid ∆⋅=

Flow rate

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Pump

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Pump input and output

Output = Flow rate and Pressure rise.

pQE fluid ∆⋅=

Flow ratepump

shaftpQE

η∆⋅

=

Input energy

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Specific Speed

( ) 4/3ρpQ

S ∆

Ω=Ω

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Pump performance

Dynamic pump

Positive displacement pump

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Pump performance range

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Performance curves

SΩ = 0.57 (Ns = 1,550) = 3.66 (Ns = 10,000)SΩ

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Steep vs. flat curves

Flat curve for closed loop system with variable flow rate Steep curve for high head and constant flow rate

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Affinity law

3

2

1

2

1

=

DD

QQ

2

2

1

2

1

=

DD

hh

5

2

1

2

1

=

DD

EE

=

2

1

2

1

NN

QQ

2

2

1

2

1

=

NN

hh

3

2

1

2

1

=

NN

EE

Impeller Diameter Impeller Speed

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Example of performance curves

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Example of performance curves

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Speed of induction motor

slipp

frpm −=120

poles Synchronous speed(rpm)

Possible Operating Speed (rpm)

2 3000 28504 1500 14256 1000 9508 750 71210 600 570

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Standard motor sizehp kW

1/8 0.091/6 0.121/4 0.181/3 0.251/2 0.373/4 0.551 0.75

1.5 1.12 1.5

2.5 1.853 2.2

hp kW

4 35.5 47.5 5.510 7.515 1120 1525 18.530 2240 3050 3760 45

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Effect of Fluid Viscosity

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Net Positive Suction Head

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Net Positive Suction Head Required

At low pressure, water can become vapor, causing cavitations.

Suction pressure must be maintained above NPSHRto avoid cavitation

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Net Positive Suction Head Available

z

)( suctionvaporatmA hpzpNPSH ++−=

Suction lift

Vapor pressure

Pressure drop in suction piping

MUST Maintain NPSHA > NPSHR

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Patm vs Elevation

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Example 6.1

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2. Operating Point

Pump performance curve

System pressure drop curve

Operating point

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Filling a tank from bottom

Pump performance curve

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Filling a tank from bottom vs. from top

Which way fill faster?

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Throttling the discharge valve

Pump performance curve

Fully open valve

Throttled valve

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Variable speed drive vs. valve throttling

Pump performance curve N1

Throttled valveFully open valve

Pump performance curve N2

Feedback signal

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VSD for pressure control

Valve 1 and 2 open

Pump performance curve N2Pump performance curve N1

Pressure set point

All valve open

Pressure signal

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Limitation of VSD

Cannot reduce speed

System curve

Feedbacksignal

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Parallel and Serial Connection

Do not exceed Maximum Allowable Working Pressure (MAWP)

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Response to Parallel Connection

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Parallel Connection of Pumps with Different Size

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Utilization of Pressure Tank

Pressure Switch

Pressure TankAir

Water

time

Pressure in tank

Pump operatePump stop

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Example 6.2

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Example 6.2

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Example 6.2

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Example 6.2

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Example 6.2

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3. Pump Selection

Best Efficiency

Energy cost is far beyond the pump cost

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Pump Specification

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Pump Nameplate

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IP RATING

The IP Code, International Protection Marking, IEC standard 60529, sometimes interpreted as Ingress Protection

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Example 6.3

Select the suitable pump for Example 5.1

200 lpm @ 50.85m.WG.

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Example 6.3 (2)

200 lpm

50.85 m

Possible selections: NM12 and NM25/20

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Example 6.3 (2)Select NM12: Trim Diameter to 198 mm

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Example 6.3 (3)Select NM12: Trim Diameter to 198 mm

Pump has efficiency of 49.5%

Power consumption 3.2 kW

Max power consumption 4kW

Select Motor size: 5.5kW

Note: follow standard motor size

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Example 6.3 (4)

hp kW

1/8 0.091/6 0.121/4 0.181/3 0.251/2 0.373/4 0.551 0.75

1.5 1.12 1.5

2.5 1.853 2.2

hp kW

4 35.5 47.5 5.510 7.515 1120 1525 18.530 2240 3050 3760 45

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Example 6.3 (5)

Dimension of NM12

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Example 6.4

Back to example 5.3, if two identical pump of the following curve is installed,predict the operating point.

0

10

20

30

40

50

0 200 400 600 800 1000 1200

อตราไหล (lpm)

ความ

ดน (m

.WG

.)

900lpm@23.1m.WG.

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Example 6.4 (2)

23.1m.WG.

= 21.6m.WG Variable with flow rate+ 1.5 m. WG. Elevation Constant

2cQhp +=∆

)900(5.11.23 2c+=51067.2 −×=c

251067.25.1 Qp −×+=∆

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Example 6.4 (3)

251067.25.1 Qp −×+=∆p∆

Q

2 pumpsin parallel

Singlepump

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3. Pump Installation

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Typical Installation

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Suction Lift

More suction lift = Less NPSHA Cavitation5 Meter lift is the maximum possible value

Foot Valve

Submersible pump

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Priming

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Self Priming Pump

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Pumping from Tank

Vortex prevention plate

Drain

Mak-up

Vent

Ove

rflow

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Eccentric Reducer

INCORRECT

CORRECT

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Installation photos

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Installation photos

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Pump Seal

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Packing Seal

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Mechanical Seal

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Homework

Exercise 6.1 and 6.2

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Case Study