CENTRIFUGAL PUMPS

    ROTATING COMPONENT &  STATIONARY COMPONENT

General components of a Centrifugal Pump

Suction and Discharge Nozzle

Cut-away of a pump showing volute casing

Solid Casing   

Seal Chamber and Stuffing Box

Seal Chamber and Stuffing Boxo        Gland: is is a very important part of the seal chamber that gives the mechanical seal the desired fit on the shaft sleeve. The gland comprises of the seal flush, quench, cooling, drain, and vent connection ports as per the standard codes like API 682.o        Throat Bushing: h a stationary device that forms a restrictive close clearance around the sleeve (or shaft) between the seal and the impeller.o       Throttle bushing refers to a device that forms a restrictive close clearance around the sleeve (or shaft) at the outboard end of a mechanical seal gland.o        Internal circulating device rerefers to device located in the seal chamber to circulate seal chamber fluid through a cooler or barrier/buffer fluid reservoir. Usually it is referred to as a pumping ring.o        Mechanical Seal: The features of a mechanical seal will be discussed in Part-II of the article.

   Rotating Components

Rotating Components

POMPA SENTRIFUGAL

End suction pump In-line pump Double suction pump Vertical multistage pump Horizontal multistage pump Submersible pumps Self-priming pumps Axial-flow pumps Regenerative pumps 

Produce a head and a flow by increasing the velocity of the liquid through the machine with the help of a impeller. 

Working Mechanism of a Centrifugal Pump

The impeller converts driver energy into the kinetic energy. 

The volute or diffuser is converts the kinetic energy into pressure energy

A pump does not create pressure, it only provides flow. Pressure is a just an indication of the amount of resistance to flow.

CAVITATIONrunning at less than 10% of its best

efficiency point

•pump installed above liquid level •pump drawing from vacuum tank

•high vapor pressure liquid •unusually long suction line

•plant is at high altitude

PENYEBAB CAVITATION

Suction Cavitation occurs when --- NPSHA < NPSHR    Symptoms

1. The pump sounds like it is pumping rocks!2. High Vacuum reading on suction line

3. Low discharge pressure/High flow

Suction Cavitation

Remedies1. Remove debris from suction line

2. Move pump closer to source tank/sump3. Increase suction line diameter

4. Decrease suction lift requirement5. Install larger pump running slower which will decrease the NPSHR pump

6. Increase discharge pressure7. Fully open Suction line valve

Causes1. Clogged suction pipe2. Suction line too long

3. Suction line diameter too small4. Suction lift too high

5. Valve on Suction Line only partially open

occurs when the pump discharge head is too high

Symptoms1. The pump sounds like it is pumping rocks!

2. High Discharge Gauge reading3. Low flow

Remedies1. Remove debris from discharge line

2. Decrease discharge line length3. Increase discharge line diameter

4. Decrease discharge static head requirement5. Install larger pump which will maintain the required flow without discharge cavitating

6. Fully open discharge line valve

Causes1. Clogged discharge pipe2. Discharge line too long

3. Discharge line diameter too small4. Discharge static head too high

5. Discharge line valve only partially open

Discharge Cavitation

12

3

1

1 2 Impeler menaikan energi Kinetik

2 3 Difuser E kin menjadi Tekanan

2

22V

dmdWao

2)( 2

223 VPP

rV

(rpm) speed- impelerukuran- tergantung

increases liquid pressure by increasing fluid velocity by action

of a rotating impeller

PRINSIP KERJA CENTIFUGAL PUMP(Aplikasi Bernouli)

2

223 2

2 ( )( ) ( ) 2 2 2 2

D N rpm D NP P rg g g g

Pump will pump all fluids to the same height if the shaft is turning at the same rpm. 

Centrifugal Pumps

tetapgPHead

2

223 2

2 ( )( ) ( ) 2 2 2 2

D N rpm D NP P rg g g g

The higher ρ, the more power is required to get the shaft to the same rpm

"constant head machines“ and not a constant pressure machine, since pressure is a function

of head and density.

2

2pompadW P V FHead z

gdm g g g

DEFINITION OF IMPORTANT TERMS

Head, Capacity,BHP (Brake horse power), Pump curvesBEP (Best efficiency point) and Specific speed.

The key performance parameters of centrifugal pumps are

CapacityThe capacity depends on a number of factors like:

Impeller size

Process liquid characteristics i.e. density, viscosity

Size of the pump and its inlet and outlet sections

Pump suction and discharge temperature and pressure conditions

Size and shape of cavities between the vanes

Impeller rotational speed RPM

KAPASITAS, HEAD DAN FLUID HORSE POWER (FHP)

2 3

2 2pumpdW D N D N

FHP m gHm g AD Ndm g

NADNDAArAVQKapasitas 22

gND

g

ND

g)r(Head

22

22

2

2

2

2

Capacity proportional to impeller speed and/or impeller diameter.

Headproportional to the square of speed and diameter

Power proportional to the cube of speed and diameter (as does NPSH)

AFFINITY LAWS FOR ROTATING EQUIPMENT

Energi/massa

Brake Horse Power Fluid Horse Power

2

( )2

pompaaodWdW P Vgz F

dm dm

FHP pompadWm

dm

PFHPBHP

MBHPHPMotor

: laju alir massaP :Efisiensi Pompa

M :Efisiensi Motor

m

Energi diterima fluida Energi dari poros pompa

Energi dari motor penggerak

BHP & FHP

Pump Performance Curve

The pump performance curve also shows its efficiency (BEP), required input power (in BHP), NPSHr, and other information such as pump size and type, impeller size, rpm etc.  

This curve is plotted for a constant speed (rpm) and a given impeller diameter (or series of diameters).   Pump curves are based on a specific gravity of 1.0.  Other specific gravities must be considered by the user.

Correlation of pump capasity to its HEAD

(D impeler dan rpm tetap)

hanya pada flow rendahtetapgP

KURVA KARAKTERISTIK POMPA

Flow

Pump DesignImpellerDiameterPump Speed

BHP = QHρg

PUMP PERFORMANCE CURVE

NPSH required is a function of the pump design

BHP Required ?

NPSH Required

EfficiencyTotal Dynamic Head

Net Positive Suction Head (NPSH)VaporP

Vaporrequired

P-PNPSH =

gh

P

Best Efficiency Point (BEP)

The H, NPSHr, efficiency, and BHP all vary with flow rate, Q. Best Efficiency Point (BEP) is the capacity at maximum impeller diameter at which the efficiency is highest. All points to the right or left of BEP have a lower efficiency

Pump Characteristic Curves

                                                                                                                                                                                                                          

Suction specific speed

SPECIFIC SPEED

PERFORMANCE COMPARISON OF CENTRIFUGAL PUMP

NADQ

2

NDH

23

23

23

21

32

1 1

sm

s

mss

mNNADNQ

23

432

43

2

smNDH

X

Q= Kapasitas pada BEP

SPECIFIC SPEED

Pompa yang ukurannya berbeda namun memiliki Ns sama , dianggap secara sama

GEOMETRI nya.

Adalah indeks disain pompa, yang menunjukkan kesamaan GEOMETRI POMPA, digunakan untuk

klasifikasi IMPELER pompa sesuai jenis dan bentuknya (proportions).

                                                                                                                                                                                                                              

Specific Speed, Ns

Radial impellers are generally low flow high head designs whereas axial flow impellers are high flow low head designs.

Specific Speed and Pump Type

SPECIFIC SPEED

Specific speed identifies the approximate acceptable ratio of the impeller eye diameter (D1) to the impeller maximum diameter (D2) in designing a good impeller.

Ns:    500 to   5000; D1/D2 > 1.5  - radial flow pumpNs:  5000 to 10000; D1/D2 < 1.5  - mixed flow pumpNs: 10000 to 15000; D1/D2 = 1     - axial flow pump

                                                                                                                                                                                                                                     

CENTRIFUGAL FLOW PUMP

                                                                                                                                                                                                                                     

Mixed Flow Pump

                                                                                                                                                                                                                                

Axial Flow Pump

REQUIREMENTS FOR CONSISTENT OPERATION

No cavitation of the pump occurs throughout the broad operating range

a certain minimum continuous flow is always maintained during operation.  

MINIMUM FLOW IN CENTRIFUGAL PUMPS

Small pumps 30% of the flow at BEP (best efficiency point).

Larger and multistage pumps 50% of BEP flow.

Reduced flow causes :Cases of heavy leakages from the casing, seal, and stuffing boX

Deflection and shearing of shaftsSeizure of pump internalsClose tolerances erosion

Separation cavitationProduct quality degradationExcessive hydraulic thrustPremature bearing failures

VERSI SATUAN BRITISH

Selecting Centrifugal or Positive Displacement Pumps

Centrifugal Positive Displacement

Flow Rate and Pressure Head 

flow depending on the system pressure or head

constant flow regardless of the system pressure

Capacity and Viscosity

the flow is reduced when the viscosity is increased

the flow is increased when viscosity is increased

Mechanical Efficiency

has a dramatic effect on the flow rate

Changing head has little or no effect on the flow rate

Net Positive Suction Head - NPSH

NPSH varies as a function of flow determined by pressure

NPSH varies as a function of flow determined by speed.

Head

SOAL SOAL POMPA

9.1. Berapa galon per menit yang dapat ditransfer oleh pompa piston yang memiliki luas area 10in2 dan panjang

stroke 5 in dengan speed 1 Hz.

5in

Speed=1HzA=1in2

1Hz- 1detik dalam 1 siklus1menit= 60 siklus

Q=A.L.NQ=1X5X60 in2 per menit

SOAL SOAL POMPA

gP

gdmdWHead ao

PQQPmPmdmdWPower s

2

2321s.lbf

ft.lbm.

9.2 Hitung hydraulic horse power untuk memompa 500 galon per menit dari inlet 5 psig ke outlet 30 psig

Q=500 galon/minP1=5 psiP2=30 psi

P1

P2

sft.lbf

sft

ftlbfPQPo

3

2

minsX

ft.lbfmin.hpX

sft.lbfPo

603300

SOAL SOAL POMPA

PQQPmPmdmdWPower s

TCPower)(Q plost 1

9.4. Suatu pompa mentransfer 50galon per menit fluida dari tekanan 30psi ke 100 psi. Power yang disuplai ke motor adalah 2.8 hp Jika perubahan elevasi dan kecepatan diabaikan hitung efiensi motor. Hitung kenaikan suhu air jika proses dianggap adiabatik

Q=50 galon/minP1=5 psiP2=30 psiPo=2,8hp

P1P2

pCPower)(T

1

Soal soal Pompa

gF

gV

gPPzzh

)

2)( 2

21212

gP

h atmosfir

max

0V0F0PjikaMax

2

2

9.5. Fluida mercury ingin dipompakan dengan menggunakan PD pump.Diasumsikan tidak ada friksi dan tekanan uap mercury diabaikan. Hitung suction lift.

ft,ft

inlbf. s lbm .ft .

ft/s. lbm/ft, lbf/in,

g.P

gP

airmerkuri 61334144232

232362714

613 2

2

223

2

Soal soal Pompa

gNDΔP 2

2

2

223 ND

g)PP(

9.6 Suatu pompa sentrifugal dioperasikan pada 1800 rpm. Jika fluidanya air, hitung perbedaan tekanan yang dapat dibangkitkan oleh pompa untuk impeler 1,3, 10 in.Hitung jika rpm 3600

418003600 22

2

1

1800

3600

NN

ΔPΔP

Soal soal Pompa

gHQmgHFHPPo

gHQFHP

9.6 Dari data flow rate dan dan head suatu kurva performa pompa hitung efiensi. Misalkan untuk Flow=5ft3/s headnya 330ft. Power=225hp.

BHPgHQ

BHPFHP

Soal soal Pompa

gNDPPΔP sd 2

2

sd PgNDP

2

2

9.5. Suatu pompa sentrifugal digunakan untuk memompa mercury. Tekanan inlet 200psi. Diameter impeler 2in. Pompa diputar dengan kecepatan 20.000 rpm. Estimasikan tekanan outlet

gNDΔP 2

2

Soal soal Pompa

gNDΔP 2

2

9.9 Suatu pompa diuji untuk fluida air pada rpm 1800 kapasitasnya 200gal per min kenaikan tekanan 50 psi. Efiensi 75 %. Kita ingin menggunakan pompa ini untuk memompa merkusri pada rpm dan flowrate yang sama. Perkirakan kenaikan tekanan, hp dan jika efisiensi sama. rpm=1800

Q= 200gal per min P= 50 psi. = 75 %.

rpm=1800Q= 200gal per min P =? psi. = 75 %.

22

32 NDNADgNDgmgHm

dmdWFHPPoPower ao