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
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