chapter 6 : pumps
TRANSCRIPT
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
2
2
1
2
1
=
DD
hh
5
2
1
2
1
=
DD
EE
=
2
1
2
1
NN
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
.)
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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