Pump Design & Selection
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Dick Hawrelak
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Presented to UWO CBE 497
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16 Oct 01
Good Design References
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Flow of Fluid Through Valves and Fittings by Crane.
Technical Paper No. 410-C.
Centrifugal Pumps and System Hydraulics,
Chem Eng’g, 4 Oct 82, p-84, by Karassik.
Chem Eng Handbook, Perry 6, Sections 5 and 6
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Primer software by Durco
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http://www.durcopump.com
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PumpSel 6.2™ (rev .07) by Durco
http://www.durcopump.com
Pump Design Stages
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Phase 2 – Process alternatives & optimization.
Phase 3 – P&IDs, preliminary layout, approx design,
specification, pre-selection, cost estimate.
Phase 4 – detailed design.
 Final layout – check piping & elevations.
 Final detailed hydraulic design & selection.
 Suitability (NPSH, SSS, Re-circulation).
 Final cost estimate.
Excel Pump Design Program
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Plant Design Programs on CD-ROM
Quick Pump Design V1.3
Contains Following Features
Line Sizing
 Control Valve Sizing
 Check Valve Sizing
 Orifice Plate Sizing
 NPSH, NS, SSS, HP calculations
 System Head Curve
 Limited Pump Selection
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Used along with Durco’s PUMPSEL and PRIMER
Draw Sketch of Pump System
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Collect physical property data (density, viscosity,
vapor pressure).
Show line details, size, schedule or wall thk, check
valves, control valves, block valves,
reducers/expanders (may have to take a WAG).
Show origin (min.) and destination pressures
(max.).
Show origin and destination elevations for static
head.
Combine services where practical & economical.
Typical Pump Sketch
Size Suction and Discharge
Lines
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Break lines into sizable sections. There
may be different sizes in any one branch.
Eg 4”, 6” and 8” sections.
Estimate the number of elbows, block
valves, fittings, etc. (WAG in Ph 2).
“Fitting” pgm in Phase III.
Expand line sizing routine for record
keeping. This will simplify phase 4
checking.
Line Size Equations
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Re No. = 6.31 ( W ) / ( d ) / ( cP )
Darcy friction factor f = 4 ( f Fanning )
f Darcy by “all-in-one” Chen Equation
DP100 = 0.000336 ( f )( W )^2 / ( DL ) / ( d )^5
Max Dp100 usually limited to 1.0 psi per 100 ft.
K = ( f ) ( L / D ) for pipe
K = ( f Turb ) ( L / D ) for valves and fittings
K total = K pipe + K valves & fittings
DP = 2.8E-07 ( K total )( W )^2 / ( DL ) / ( d )^4
Abs roughness e = 0.00015 for clean pipe, ft.
Abs roughness e = 0.0004 for dirty pipe, ft.
Size Check Valves in Each
Discharge Line Branch
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Line sizing program built-into Pump pgm.
Check pipe spec for type of check valve.
Check minimum line velocity to keep ChV in
open position. Prolonged operation at
reduced rates may cause ChV chatter and
damage to ChV.
Operation with damaged ChV is extremely
hazardous.
Typical Check Valve Equation
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For a Swing Check Valve (see Crane, page
A-27)
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K = 100 ( f Turb ) for pressure drop
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Minimum Velocity, fps = 35 / ( DL )
Size Orifice Plates in
Each Branch
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See Line sizing routine.
Orifice Plate pressure drop
usually in three ranges.
Typically 0.5, 1.0 or 2.0 psi
Typical Orifice Equation
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Beta = d1 / d2 should be in range 0.2 to 0.7
d1 = orifice dia., d2 = pipe dia., inches
Re No. based on d2, the pipe diameter
W = 1891 ( d1 )^2 ( C ) (( DP )( DL))^0.5
C = Flow Coefficient for square edged
orifices (see Crane, page A-20)
C = Function of Re No. and Beta ratio
C should be in range 0.6 to 0.8
Control Valves
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Select each branch with control valves and use
line size routine to size control valves assuming
Fisher Equal Percentage type valves.
Poor CV selection – no control, pump running
on by-pass…may need two control valves.
If too large DP taken across control valve, it may
be better to trim impeller, save CV wear & energy.
Pump program should use CV in controlling line.
DP CV / (DP CV + DP fric) = approx 0.1 to 0.3.
Default DP control valve = 10 psi.
Typical Control Valve Equations
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Cv = ( USGPM )( SG / DP )^0.5
Cv = Liquid Sizing Coefficient.
SG = Specific Gravity.
DP = Pressure Drop (10 psi default)
Typical control valve is an equal
percentage type valve.
Cv depends on valve size, % valve
opening, and flow.
Blocked-in Operation.
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Determine features required for blocked-in operation.
Low flow shut-down.
 High temperature shut-down.
 Recycle plus cooling.
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Pumps can explode in a short period of time if left
running while blocked-in and no high temperature
shut-down is provided.
Pump explodes, pieces rocket 275m, hits truck, kills
driver.
Pump leaks under high pressure, liquid catches fire
and destroys plant.
Suction Conditions
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Determine NPSH available.
NPSH = SP – VP + HL – DP friction all in ft of liq.
Boiling liquids, SP = VP. Raise height or reduce DP.
Poor NPSH causes pump cavitation, high vibration
& ultimately pump failure (hazard).
Pump fails to perform as designed without NPSH
available greater than NPSH required.
Typically, NPSH avail 12 ft. vs 10 ft. req’d.
Pump Vendor will tell you NPSH required based on
pumps selection.
System Head Curve
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Determine Controlling Branch – I.e the
one that requires the maximum
differential head.
Determine the system curve for all
items except the control valve.
For Dp at reduced USGPM, assume
DP is proportional to the square of the
flow.
Include static head.
Pump Selection
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Hundreds of pumps to select
from.
Which selection is best?
Which RPM to use?
What HP size & type of motor to
select, explosion proof, TEFC?
Download Durco PUMPSEL and
PRIMER on internet (program is
free).
http://www.durcopump.com
Durco PUMSEL Program Input
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From Quick Pump Design V1.3 enter:
 Design USGPM
 System head, in ft.
 Specific Gravity
 Pumping temp, Deg F
 Viscosity in Centipoise
 NPSH available in ft.
 3 points from system curve.
PUMPSEL Output
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Selects all available pumps
Gives Impeller sizes
Gives HP and NPSH Required
Gives a cost estimate (PRIMER)
Gives options for types of pumps
Gives all kinds of help on all features.
PUMPSEL is a must for any design
group.
Program also available from Gould.
Typical Pump Head Curves
Selected Pump
Suction Specific Speed, SSS
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SSS is an Index number descriptive of the suction
charateristics of a pump impeller.
SSS = (rpm)(Q @ BEP)^0.5 / (NPSH @ BEP)^0.75
Pumps operating at SSS greater than 11,000 had a
high failure frequency (hazard).
Low capacity operation causes inlet recirculation,
impeller erosion, shaft deflections, bearing failures
and seal problems which lead to leakage.
Pump program predicts recirculation as % of SSS.
Dissolved Gases
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Absorbed gas follows Henry’s Law xa
= (pp / Pt) / H.
Dissolved gases are like entrained
bubbles. Residence time in suction
vessel may be too short.
Dissolved gases causes problems
similar to NPSH cavitation.
Prevent vapor entrainment with vortex
breakers.
Material Transfer
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Need multiple checks on
quantity of material transferred
to storage.
Weigh scales, level checks,
mass = (flow rate)(time) on
computer.
Time control EBVs to minimize
Water Hammer problems.
Excess Flow Protection
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Pumps cannot be allowed to run out
on the impeller curve, may burnout
motor if motor not selected for
runout.
May need excess flow protection.
Repeat Design in Phase IV
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All of the above details are
checked again in Phase IV
Engineering.
Necessary to have good
documentation.
Poor Phase III Design &
Selection means rework during
expensive Phase IV stage.