pumps selection lecture

Intro to Pumps and their Selection

MEEN 5312Optimization of Thermal Systems

Turbo-machinery

Turbo-Machinery Pumps Compressors Fans Blowers Turbines Miscellaneous:

Piping Tubing Valves Flow meters Storage tanks Gages others

Schematics of Turbo-machinery

Pumping Systems and Pumps

Importance of Pumping Systems• Pumping systems account for nearly 20% of the

world’s electrical energy demand.• 25-50% of the energy usage in certain industrial

plant operations. • Widespread use of pumping systems:

• domestic, commercial and agricultural services• municipal water and wastewater services• industrial services for food processing, chemical,

petrochemical, pharmaceutical, and mechanical industries

Objective of a Pumping System

• Transfer of liquid from one place to another place:• water from an underground aquifer into a

water storage tank)• Circulate liquid around a system

• cooling water or lubricants through machines and equipment)

Pumping System

• Pumps• Prime movers: electric motors, diesel

engines or air system • Piping for flow of fluid• Valves to control the flow in the system• Other fittings, controls and instrumentation

Types of Pumps Kinetic (Dynamic)

Pumps Examples: a centrifugal

pump, an radial pump Positive Displacement

Pumps Examples: a gear pump,

a reciprocating piston pump

Classification of Pumps

Dynamic Positive Displacement

Centrifugal Special effect Rotary Reciprocating

Internal gear

External gear Lobe Slide

vane

Others (e.g. Impulse, Buoyancy)

Pumps

Dynamic Positive Displacement

Centrifugal Special effect Rotary Reciprocating

Internal gear

External gear Lobe Slide

vane

Others (e.g. Impulse, Buoyancy)

Pumps

Kinetic (Dynamic) Pumps

Kinetic pumps add energy continuously to increase the fluid velocity (kinetic energy) within the pump element such that subsequent velocity reduction in pump volute produces a pressure increase (potential energy).

Dynamic Pumps

Positive Displacement Pumps

Total and Static Head

• Total Head• Resistance of the

system• Two types: static and

friction

• Static head• Difference in height

between source and destination

• Independent of flow

destination

source

Statichead

Statichead

Flow

Friction Head

• Friction head• Resistance to flow in

pipe and fittings• Depends on size, pipes,

pipe fittings, flow rate, nature of liquid

• Proportional to square of flow rate

• Closed loop system only has friction head(no static head)

Frictionhead

Flow

Total Head

Systemhead

Flow

Static head

Frictionhead

Systemcurve

System head

Flow

Static head

Friction head

Systemcurve

Pump Performance Curve

Pump Performance Curve

Relationship between head and flow• Flow increase• System resistance

increases• Head increases• Flow decreases to zero

• Zero flow rate: risk of pump burnout

Head

Flow

Pump Characteristic Curve Head (ft, m) Flow rate (gpm. m3/s) Hydraulic efficiency

(%) Impeller diameter (m) Power (hp, kW) Net Positive Suction

Head required (NPSHR)

Pump Operating Point

• Duty point: rate of flow at certain head

• Pump operating point: intersection of pump curve and system curve

Flow

Head

Static head

Pump performance curve

System curve

Pump operating point

System Curve & Operating Point

Cavitation

• Cavitation or vaporization: bubbles inside pump

• If vapor bubbles collapse• Erosion of vane surfaces• Increased noise and

vibration• Choking of impeller

passages

Suction Lift

Pumps need suction (low pressure) to draw liquid into.

Maximum suction lift depends on pump design (NPSHR), pressure applied on the liquid surface and the vapor pressure water (NPSHA).

NPSHR & NPSHA

NPSHR (Net Positive Suction Head Required)pump suction needed to avoid cavitation

NPSHA (Net Positive Suction Head Available)how much pump suction exceeds liquid

vapor pressure

NPSHR It is the required

pressure at the pump’s suction (eye) to operate the pump at a given flow

Depends on the design of the pump

Given in pump characteristics curve by the manufacturer

NPSHR

NPSHA

Depends on Elevation of the

suction supply Elevation of the

installation Friction in the suction

line Vapor pressure of the

liquid being pumped NPSHA = Ha-Hs-Hvp

Pump Selection

System (technical)Flow rate, head, speed, power, etc

Liquid propertiesViscosity, temperature, flammable, etc

Safety/environmentalUL label, regulation, enclosure, etc

Economy/reliabilityLubrication, operator, maintenance, etc

Pump Selection Guide (Goulds)

Liquids

Zoom View

Choose a model

Specific Speeds

4/3ftH

gpmQrpmN sd

4/32

3

/

//

mHsmg

smQsradN s

ssd NN 2733

Specific Speed (Nsd vs Pump Size)

34

Assessment of pumpsAssessment of pumps

• Pump shaft power (Ps) is actual horsepower delivered to the pump shaft

• Pump output/Hydraulic/Water horsepower (Hp) is the liquid horsepower delivered by the pump

How to Calculate Pump PerformanceElect rical E

qui pme nt/

Pum

ps

Hydraulic power (Hp):Hp = Q (m3/s) x Total head, hd - hs (m) x ρ (kg/m3) x g (m/s2) / 1000

Pump shaft power (Ps):Ps = Hydraulic power Hp / pump efficiency ηPump

Pump Efficiency (ηPump): ηPump = Hydraulic Power / Pump Shaft Power

©© UNEP 2006 UNEP 2006

hd - discharge head hs – suction head, ρ - density of the fluid g – acceleration due to gravity

Dynamic Pumps

Dynamic Pumps

• Mode of operation• Rotating impeller converts kinetic energy into

pressure or velocity to pump the fluid

• Two types• Centrifugal pumps: pumping water in industry – 75%

of pumps installed• Special effect pumps: specialized conditions

Parts of a Centrifugal Pump

Impeller Blades/Vanes Volute Casing Seal Shaft Motor

38

©© UNEP 2006 UNEP 2006

Type of PumpsType of Pumps

Centrifugal PumpsElect rical E

qui pme nt/

Pum

ps

How do they work?

(Sahdev M)

• Liquid forced into impeller

• Vanes pass kinetic energy to liquid: liquid rotates and leaves impeller

• Volute casing converts kinetic energy into pressure energy

40

©© UNEP 2006 UNEP 2006



qui pme nt/

Pum

ps

Impeller Sahdev)

• Main rotating part that provides centrifugal acceleration to the fluid

• Number of impellers = number of pump stages

• Impeller classification: direction of flow, suction type and shape/mechanical construction

Shaft• Transfers torque from motor to impeller during pump

start up and operation

41

©© UNEP 2006 UNEP 2006



qui pme nt/

Pum

ps

CasingsVolute Casing (Sahdev)• Functions

• Enclose impeller as “pressure vessel”• Support and bearing for shaft and impeller

• Volute case• Impellers inside casings• Balances hydraulic pressure on pump shaft

• Circular casing• Vanes surrounds impeller• Used for multi-stage pumps

Let’s watch videos on Centrifugal Pump! http://www.youtube.co

m/watch?v=9nL1XhKm9q8

http://www.youtube.com/watch?v=gZWugqF3ZFQ

http://www.youtube.com/watch?v=9nL1XhKm9q8







Positive displacement pumps adds energy periodically by application of force to one or more movable boundaries of enclosed fluid containing volumes resulting in direct increase in pressure up to the value required to overcome the system resistance.

Two Main Types of PDP

• Reciprocating pump• Displacement by reciprocation of piston plunger• Used only for viscous fluids and oil wells

• Rotary pump• Displacement by rotary action of gear, cam or vanes• Several sub-types• Used for special services in industry

PD Pumps

By definition, PD pumps displace a known quantity of liquid with each revolution of the pumping elements (gears, rotors, screws, vanes).

PD pumps can handle fluids of all viscosities up to 1,320,000 cSt capacities up to 1,150 m3/hr (5,000 GPM) pressures up to 700 Bar (10,000 PSI)

Some PD Pumps

Rotary Pump Selection Guide

Comparison

Pumps in series and parallel

Pumps in series To increase the head

for the same flow rate

Pumps in Parallel

Pumps in parallel To increase the flow

rate for the same head

Affinity Law

Flow rate (capacity) Q , D

Head H D2

Power P D3

In Equation Forms

Effect of Rotational Speed

• Affinity laws: relation speed N and• Flow rate Q N• Head H N2

• Power P N3

• Small speed reduction (e.g. ½) = large power reduction (e.g. 1/8)

Variable Speed Operation

Variable Speed Drive (VSD)

• Speed adjustment over continuous range• Power consumption also reduced!• Two types

• Mechanical: hydraulic clutches, fluid couplings, adjustable belts and pulleys

• Electrical: eddy current clutches, wound-rotor motor controllers, Variable Frequency Drives (VFDs)

References

Pump Types www.pumped101.com Pump Selection Guide by Goulds Pumps Bulletin 723.4 by Goulds Pumps Fundamentals of Fluid Mechanics by Munson et al. www.cheresources.com www.energyefficiencyasia.org

http://www.pumped101.com/

http://www.cheresources.com/

pumps selection lecture

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