Section 6B

PUMPS

Main resources:
General: Design Practices Section 10
Centrif Pumps: API 610, GP 10-1-1, EN-809
Recip Pumps: API 674, GP 10-2-1
Diaphragm P’s: API 675, GP 10-2-3
Rotary Pumps: API 676, GP 10-2-2
Sealless Pumps: API 685 6B.1
Shaft Seals: API 682, GP 10-1-3, TMEE-23
 Pumps - Agenda
• Types of Pump
• Pump Performance Calculations - Overview
• Centrifugal Pumps - General Characteristics
• Reciprocating Pumps - General Characteristics
• Centrifugal Pumps
– Selecting to avoid NPSH problems
– Service Requirements and control system issues
– Electric Motor Sizing
– Performance Issues
– Shaft Seals
– Materials
• NPSHa Calculations
• Pump Electrical Power Calculations
• Calculating the effect of Resizing Impellers

6B.2
 Pump Types
• Two Basic Types of Pump
– Dynamic
• Centrifugal or Axial pumps
• The most common type of pump used in process industries
• Impart velocity to the pumped liquid and convert the velocity
to pressure in a diffusing flow passage
• Lower maintenance than positive displacement pumps

– Positive Displacement
• Reciprocating, Diaphragm (metering) or Rotary
• Less common but still used for specific applications
• Operate by forcing a fixed volume of liquid from the inlet
zone to the discharge zone
• Either intermittent or continuous

6B.3
 Pump Classification
PISTON

RECIPROCATING PLUNGER

DIAPHRAM
POSITIVE
DISPLACEMENT GEAR
SCREW
PUMPS ROTARY
VANE
CAM
RADIAL FLOW
CENTRIFUGAL MIXED FLOW
AXIAL FLOW
DYNAMIC JET
SPECIAL GAS LIFT
HYDRAULIC RAM
6B.4
 Pump Performance Calculations - Overview

• Key Parameters:
Head = (P2 - P1) * 10.2 / SG (metres)
Flow = Suction flow expressed as Volume (m3/h)
Efficiency = Power required with no losses / Actual Shaft Power
NPSH = Head of liquid at suction above vaporisation pressure
(see section on calculating NPSH)
NPSHa = Available NPSH
NPSHr = NPSH Required by the pump to avoid “cavitation”
Shaft Power = Flow * SG * Head * 9.81 / Efficiency * 3600

• Note: Pump head is based on DeltaP (P2-P1);

Compressor head is based on Pressure Ratio (P2/P1)
Flow m3/h; Head m; Power kW; Pressure bar

6B.5
 Pump Performance Curves
Recips vs Centrifs

Note:
• Effect of Viscosity
• Flow Range

6B.6
 Centrif Pump Performance
Effect of SG and Viscosity
• Centrifugal Pumps run at a defined head and volume
flow.
• Thus a pump designed for 100m of head at a flow of 50
m3/h and efficiency of 80% will give the following:
Fluid SG Pressure Rise (bar) Power (kW)
Water 1.00 9.8 17
LPG 0.53 5.2 9

• High viscosity fluids reduce centrif pump performance.

– Vendor curves typically quoted for water.
– See DP X-E for correction curves or use Pegasys
Pump Rating program
6B.7
 NPSH

• The force suppressing cavitation is the margin by which the

local static pressure of the fluid exceeds the vapour
pressure at the operating temperature.
• This margin, converted into an equivalent head of the
pumped fluid, is termed the Net Positive Suction Head or
NPSH.
• The magnitude of the pressure losses incurred as the fluid
enters the pump are a function of the pump geometry and
fluid rate. The head equivalent of these losses is termed
the required NPSH (NPSHR). Values for this are provided by
the pump vendor.
• To avoid cavitation, the available NPSH (NPSHA) from the
suction system must be greater than the NPSHR.

6B.8
NPSH - PUMP PRESSURE PROFILE

Required NPSH
6B.9
 CAVITATION
• In all pump types, the fluid incurs pressure losses due to friction
and turbulence as it flows from the inlet flange to the impeller,
rotor or cylinder.
• If the pressure is reduced to that of the fluid vapour pressure,
vapour pockets will form.
• These bubbles are eventually swept into regions of high pressure
where they collapse.
• When this occurs, the pump is said to “cavitate”.
• This results in vibration, noise, reduced pump capacity and
erosion or pitting of the metal surfaces.
• Effect is worst with pure fluids (eg Water).

6B.10
 PUMP TYPE SELECTION

• Pump type selection is generally influenced by:

– Flow Rate
– Head Requirement
– Maintenance and reliability
– Viscosity at pumping/ambient conditions
(eg screw pump for bitumen)
– Flow control
• Pump style/construction depends upon:
– Discharge Pressure (eg: barrel pump at high pressure)
– NPSHa (eg: Vertical suspended for low NPSHa)
– Fluid temperature (special features for high and low temp)
– Installation constraints (inline vs overhung vs between-bearing)

6B.11
 CENTRIFUGAL PUMPS - General Characteristics

• Available for large range of duties.

– Not normally recommended for flows < 4 m3/h or heads > 2000m
• Designed for min 3 years continuous operation between failures (although
some duties do not currently meet this)
• Suitable for most fluids (typical viscosity limit of 200 cSt)
• Suitable for slurries (But may need special design to avoid erosion)
• Four main Types:
– “Overhung” single impeller.
– “Inline” single impeller
– Horizontal Between Bearings (one or more impellers)
– Vertically Suspended
• Pumps are normally direct driven without gearbox. Can use single stage
vertical inline pump with integral gearbox (Sundyne) for high head
applications

6B.12
Horizontal Single Stage Overhung Pump

6B.13
Inline Single Stage Pump (direct drive)

6B.14
Pump Types - Gear Driven, High Speed Inline

6B.15
Multi Stage Horizontal Pump

6B.16
 Centrifugal Pump - Application Range

Application
Range
DP X-A
table 2B

6B.17
 Positive Displacement Pumps
General Characteristics
• General Characteristics:
– Low capacity at high head
– Available discharge pressure not affected by fluid density
– Clean fluids (recip pumps not good for entrained solids)
– Need relief valve to protect discharge line
• Common types include:
– Reciprocating Pumps
• Fixed Flow Rate. Pulsating Flow
• Integral designs available using Steam (in piston) as driver
– Diaphragm Pumps (Metering)
• Can be variable flow rate, Pulsating Flow
• Do not require seals
• Integral designs available using Air as driver
– Screw, Gear and Vane Pumps (Rotary)
• Fixed Flow Rate, Continuous (ie non pulsating) Flow
6B.18
 Reciprocating Pumps
– Generally pressures above 80 bar
– Flexible with respect to fluid characteristics and conditions
– Complex, expensive, high maintenance items
– Examples: Ammonia plant feed, HP water injection
– Require Pulsation Dampers on pipework
– Need to include the effect of “acceleration head” on NPSHa
– “Packing” used to prevent leakage from piston rod

6B.19
 Diaphragm Pumps
• Accurate flow control (around 1 %)
• Capacity up to 5 m3/hr
– higher available with multiple pumping heads
• Generally low temperature and low pressure applications

• Diaphragm may
have two layers
with leakage
detector

6B.20
 Rotary Shaft Pumps

– Screw, Gear and Vane types

– Good for high viscosity fluids
– Pulsation free flow
– Generally clean services (except single rotor screw type)
– Low to medium flow rates
– High discharge pressures possible

6B.21
 Centrifugal - Selecting to avoid NPSH
problems
• High flow pumps require more NPSH
– Governed by equation
min NPSHr = ((0.75 * N * sqrt(Q)) / 12000) ^ 4/3
A 3000 rpm pump requires 27 m @ 4000 m3/h
– 4 ways of mitigating:
• Reduce speed of pump (add more impellers/larger diameter)
• Use “inducer”. Reduces pump flow range - not very effective
on multistage pumps.
• Use vertical suspended pump - typical solution for light ends
pumps
• Use “Double suction” pump. Thus split the inlet flow across two
impellers.

6B.22
Pump Types - Double Suction Pump
Inlet flow is divided between two
impellers

6B.23
 Pump Types -
Vertical Suspended

Inlet to first impeller is 2-3 metres

below ground, hence increasing
NPSHa to the impeller

6B.24
 Centrifugal Pumps - Service Requirements
• External continuous flush may be required for services with solids and
optionally for hot services.
– Flush supply to fill pump when not running may also be required for viscous
services
• Cooling water required for:
– Bearing cooling for services above around 210 degC (0.5 - 1.5 m3/h)
– Seal flush cooling for hot water services and many high temperature
Hydrocarbon services
– Seal barrier fluid cooling above for dual seals above around 80 degC
• Steam “quench” required for most services above 180 C
• Drain (to closed header) required for some services (see GP 3-6-4)
– Mainly for toxic and autoignition fluids. Used to empty pump for maintenance

6B.25
 Centrifugal Pumps - Service Requirements
• Warm-up facilities required for all services > 230 C and for large pumps at
lower temps.
– Use back-flow from discharge. Typical warm-up may take 2 hours
• Suction strainers normally only used for startup
– Permanent strainers required for some services (eg coking services) and for
diaphragm pumps.
– Allow 0.07 bar DeltaP for permanent strainers in NPSHa calcs.
• Venting required for some services to prevent vapour locks (especially
low temperature, high vapour-pressure services)
– Avoid high points in suction piping
• Safety Valve required on suction of high pressure pumps
• Low flow recycle required if min process flow < min allowed (typically 30%
of design flow)
– Mandated for Boiler Feedwater and some high deltaP pumps.
– Required for flow control of recip pumps

6B.26
 Protection Against Low-Flow

• Methods

6B.27
 Caution - Pumps in Series

• System Design Pressure Must Be Suitable for the Shutoff

Pressure of Both Pumps Combined
• Extra Controls and a Safety Valve May Be Required

6B.28
Caution - Pumps in Series (Cont’d)

Figure 18
6B.29
 Caution - Pumps In Parallel

• Parallel Operation Might Result in Unbalanced Flow, with Less

Than Minimum Flow in One Pump

• This Can Occur if Curves Are Flat, and

– Speeds are Different (One Motor Driver, One Turbine)
– Impellers Are Not Identical
6B.30
 Centrifugal Pumps -
Common Control Systems
Single Centrifugal Pumps

• Throttle Discharge Flow

– Most Common

• Variable Speed
– Only for Large Pumps with Significant Portion of
Operation at reduced Flow
– May offer significant power saving

• Suction Throttling Not Used

6B.31
 Electric Motor Sizing

– Pumps operating singly (ie not in parallel)

• Sized for 1.1 x power at process rated point
this “rated point” for power calculations should be at
highest flow, SG and viscosity.
– Pumps operating in parallel
• Sized for pump “end of curve” operation with max SG and
viscosity. In this case, no 10% margin is normally added
– Do not unnecessarily oversize motors
• Motors have lower efficiency at part load.
• Motor and switchgear more expensive

6B.32
 Centrif Pump Performance
Typical Characteristic
• Note Steepness of head/flow curve.
– Normally require min 10%, max 20% head rise from rated flow
to “shut-off” Rated point

“Shut-off”

Q = Pump Capacity
H = Differential Head
P = Shaft Power
 = Pump Efficiency
Min Continuous Flow

6B.33
 Centrif Pump Performance
Effect of Impeller Diameter
• Note Effect of Impeller
Diameter.
– Max size impeller rarely
installed. API 610
requires margin for 5%
head uprate from impeller
size change.

6B.34
Q (m3/h)
 Pump Shaft Seals

• Mechanical Seals
– Most common seal type for centrifugal pumps
• Packing
– Centrifugal pumps: Mandated for Fire water pumps.
Occasionally used for water service
– Used on piston rod of piston and plunger pumps
• Sealless Pumps
– Small centrifugal pumps < 150 HP. Motor in fluid or
driven via “magnetic coupling”
– PD Diaphragm pumps

6B.35
 Mechanical Seals - Overview

 Good working single seal

designs allow very low vapor
leakage < 1,000 wppm

 No Detectable Emissions using

double seal or inert gas seal
designs

 Seal is typically the most

troublesome component of pump
but mechanical seal life of 3- 5
years is possible

6B.36
Mechanical Seal - Single Seal arrangement

6B.37
Mechanical Seal - Dual Seal arrangement

6B.38
 Packing
small leakage needed for
lubrication (drops/min)

Simple Packing

Packing with barrier fluid injection

6B.39
 Sealless Pumps

– Advantages
• Zero emissions - used for toxic / hazardous liquids
• Very good reliability in clean liquid services
– Disadvantages
• Bearings immersed in and lubricated by pumped fluid --
susceptible to damage if fluid is not clean
• Rotating shear and electrical/magnetic slip losses add heat to
pumped fluid passing through motor -- can result in run dry
operation / bearing failure
• Apply strong magnetic fields directly to pumped fluid --
susceptible to solid buildup from corrosion elements (iron)
normally present in Petro-Chem Plants

6B.40
Sealless Pump - Mag Drive Pump

6B.41
 Seals - Control Level

• Seal design is defined generally defined by API 682

• This allows several choices of arrangement.
• ExxonMobil uses a concept called “Seal Control
Level” to define the consequence of seal leakage and
thus the arrangement to use
– Level 1 is lowest risk (eg cold water)
– Level 6 is highest risk (eg HF Acid)

6B.42
 Seals -Control Level Examples
CONTROL DEFAULT INSTRUMENTS TYPICAL PROCESS CONDITIONS
LEVEL ARRANGEMENT (SEE TMEE 023 FOR MORE DETAIL)
1. Single Seal + -  Clean Water < 65 degC
API restrictive Bushing
2. Single Seal + -  HC with Narrow boiling range and Pvap < 1 bara
Floating Carbon Bushing  HC with Medium/Wide boiling range and Pvap < 13.8 bara
and < 40% vaporisation
 Water >= 65 degC and non-acidic aqueous
 R4 respiratory exposure class
3. Single Seal + Leakage Detection  HC with Pvap > 13.8 and Medium/Wide boiling range
Segmented Floating and < 40% vaporisation
Carbon Bushing  Rich H2S streams where area monitors are installed.
(> 2% H2S in leaked vapour)
R3 respiratory exposure class
 Fluid burns with invisible flame + fire detectors
4. Single Seal + Leakage Detection  Narrow boiling range HC with Pvap > 1 bara and < 13.8 bara
Dry Running Backup seal  HC with Pvap < 13.8 bara and >40% vapourisation
 Acids with pH < 4
5. Unpressurised Dual Seal Leakage detection  HC with Pvap >= 13.8 bara @ 38 degC: and either Narrow boiling
(+ bearing monitoring ?) range or >40% vapourisation
 Rich H2S streams with no area H2S monitoring
(> 2% H2S in leaked vapour)
 Fluid burns with invisible flame with no fire detectors
6. Pressurised Dual Seal Leakage detection  HF Acid, Phenol
(or sealless pump) (+ bearing monitoring ?) R1 and R2 respiratory exposure classes
 Vacuum Bottoms

6B.43
 Seal Flushing

• Flush Fluids flow inboard of a seal.

• Main purposes:
– Cool the seal
– Prevent solids from reaching the seal
• Source of flush may be the pump discharge or an external
source
• If pump discharge is used, then may include a cooler and/or
inertial separators
• API 610 defines the standard arrangements. Examples:
Plan 02 = No flush
Plan 11 = Flush from discharge
Plan 23 = Recirculating flush with cooler
Plan 32 = Flush from external source
6B.44
 Seal Quenching

• This is fluid (normally steam or water) that flows outside of

the primary seal
• Main purposes
– Remove any leakage from the seal area (eg to prevent
coking, salt deposits)
– Cool high temperature seals (with steam)

• API 610 defines the standard arrangements. Example:

Plan 52 = External (steam) quench

6B.45
Pump Materials - API Material Selection Guide

Materials selection Guide (part of) API 610 Appendix G-1

6B.46
 Pump Materials - API Materials List

S series = Carbon Steel casing; Most streams

C series = 12% chrome casing Hot water, Hydrocarbons > 400 degC
A series = Austenitic Stainless Steel casing Corrosive fluids eg Hot Sulphuric Acid
D series = Duplex Stainless Steel casing Sulphur, seawater ?

Materials vs Material Class (part of) API 610 Appendix H-1

6B.47
 NPSHa Calculation - Overview

• The NPSHA is calculated from:

NPSHA = HP - HVP + HS - HF

HP = Pressure head at liquid surface

HVP = Fluid vapour pressure head
HS = Static height difference between liquid level and
pump datum
HF = Suction line frictional losses

6B.48
 NPSHa Calculation Example
Bubble Point Liquid
3.5 barg S.G. COND = 0.70

1.75 m

Suction Line: 15 m of 6" line,

3 x 90° elbows, 1 gate valve
Total equivalent length = 22.8 m

3.75 m

0.60 m

• P of suction piping = 9.7 kPa/100m  1.42m of liquid/100m

PF of suction system = 1.42/100 * 22.8 = 0.32 m (HF).

6B.49
NPSHa Calculation Example

NPSH A  HP  HVP  HS  HF

 3.5  1.0   10 5  Hp
  9.81  700 
 
 4.5  10 5  Hvp
  9.81  700 
 
 3.75  0.60 Hs
 0.32
HF

 2.83 m of liquid

6B.50
 NPSHa Calculation Example

• This example illustrates that for most situations, the fluid is

at its vapour pressure the equation may be simplified to:
NPSHA = HS - HF

• NPSHa safety margin

– NPSHa quoted on data sheets should normally include a
10% safety margin.
– This approach varies and some affiliates apply the
safety factor in a different way.
– Do not increase the safety factor without justification.
The impact can be expensive.

6B.51
 Pump Power Calculations
P kPA   Q m 3 / hr 
• Hydraulic Power: kW 
3600

P kPA   Q m 3 / hr 
• Shaft Power: kW 
EO  3600

EO, pump efficiency, may be obtained from DP’s or Vendor Information

• Minimum Driver Power = Shaft Power x Load Factor

Load factor of 1.1 is typically selected for electric motor drivers

After applying the load factor select the appropriate motor size

6B.52
 Centrif Pump Efficiency (typical)

DP X-A
Table 5B

6B.53
 Motor Power Calculations

P kPA   Q m 3 / hr 
• Power Consumption: kW 
EO  EM  3600

EM, motor efficiency, may be obtained from DP XI-L, Table 1

Installed Motor Power kW 

• Connected Load kW 
EM100

EM100 is the motor efficiency at 100% load

6B.54
Motor Efficiency

6B.55
 Power Calculation Example

• Calculate the shaft power and motor size for the following
pump:
Pump P = 10.34 bar (1034 kPa)
Liquid Rate = 227 m3/hr
Liquid S.G.c = 0.649

Pump Head H 
P

1034   162 .5 m
S.G.C  g 0.649  9.81

For H = 162.5 m and Q = 227 m3/hr, EO = 71%

Shaft Power 
1034 227   1034 227   91.8 kW
3600  EO 3600  0.71

6B.56
 Power Calculation Example

EO = 71%

162.5 m

227 m3/hr
6B.57
 Power Calculation Example

• Assuming load factor of 1.1

Minimum motor size = 91.8 x 1.1 = 101 kW

Next available motor size is 112 kW (150 HP)

Motor Operating Load 

91.8  82%
112 

At 82% load, EM for 112 kW motor is 89%

Power Consumed 
91.8  103.1 kW
0.89 
At 100% load, EM100 for 112 kW motor is 91%

Connected Load 
112   123.1 kW
0.91
6B.58
Power Calculation Example

6B.59
 Pump Affinity Laws -
Calculating the effect of changing impeller diameter
• The variation of head, capacity and power with speed and
impeller diameter follow definite rules known as
“The Affinity Laws”.
Flow Q  Peripheral Speed
N  D  D = impeller diameter
Q2  Q1  2  or Q2  Q1  2  N = impeller RPM
 N1   D1 

Head H  Peripheral Speed 2

2 2
N  D 
H2  H1  2  or H2  H1  2 
 N1   D1 

Power HP  Peripheral Speed 3

3 3
N  D 
HP2  HP1  2  or HP2  HP1  2 
 N1   D1  6B.60
 Pump Affinity Laws

• The following example shows the effect on pump head and

power of changing from a 10” to 11” impeller.
10” 11”
Flow Head Power Flow Head Power
100 335 200 110 405 266
200 335 220 220 405 293
600 325 290 660 393 386
1000 295 355 1100 357 472
1400 245 412 1540 296 548
 11 
Flow 11"  100     110
 10 
2
 11 
Head 11"  335     405
 10 
3
 
11
Power 11"  200     266
 10  6B.61
 Pump Affinity Laws
IMPELLER CHANGE
450 1000
11” IMPELLER
400 900
350 10” IMPELLER 800
300 700

POWER
HEAD

250 600
200 500
11” IMPELLER

150 400
10” IMPELLER
100 300
50 200
0 100
0 200 400 600 800 1000 1200 1400 1600 1800
FLOW
6B.62