Pumps

Sistem Dan Permesinan Kapal

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References: Centrifugal Pump Handbook third edition Winterthur,

Switzerland, Sulzer Pump Ltd Handbook of pumps & Pumping, Brian Nesbit, Elsevier

Science & Technology books Pump Handbook third edition McGraw Hill

Pumps System Energy Efficiency Ref. Guide, CEATY International

Introduction to Marine Engineering Marine Auxiliary Machinery

Maritime Engineering Reference Handbook

Introduction

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Pumps : sebuah alat yang berfungsiuntuk menambah energy ke suatucairan atau yang menyebabkanpenambahan tekanan danmemungkinkan terjadinya gerakan darifluida tersebut

Energi yang ditambahkan oleh pompake fluida yang lewat dinamakan total head

Pumps Functions

Transfer liquid

Circulate liquid

Components of a pumping system

are:

Pumps

Prime movers

Piping Valves,

Other fittings, controls and

instrumentation

End-use equipment,

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Head atau energy per-unit mass flow rate fluidaumunya terdiri dari

Pressure head karenagaya per-unit area fluida

Dynamic / velocity head yang diukur dari energy keinetik fluida

Potential atau static head karena ketinggian cairan

Bernoulli Equation

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Flow rate depend on friction

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General Pumping Fundamental

Pressure is needed to pump the liquid through the system at a certain rate. This pressure has to be high enough to overcome the resistance of the system, which is also called head. The total head is the sum of static head and friction head.

Static head

Static head is the difference in height between the source and destination of the pumped liquid

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Static head consists of:

Static suction head (hS): resulting from lifting the liquid relative to the pump center line. The hS is positive if the liquid level is above pump centerline, and negative if the liquid level is below pump centerline (also called suction lift)

Static discharge head (hd): the vertical distance between the pump centerline and the surface of the liquid in the destination tank

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Friction head:

This is the loss needed to overcome that is caused by the resistance to flow in the pipe and fittings.

It is dependent on size, condition and type of pipe, number and type of pipe fittings, flow rate, and nature of the liquid.

In most cases the total head of a system is a combination of static head and friction headTotal head = Static head + friction head

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Pump performance curve :

The head and flow rate determine the performance of a pump.

The figure shows a typical curve of a centrifugal pump where the head gradually decreases with increasing flow.

As the resistance of a system increases, the head will also increase.

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Typical characteristic curve of centrifugal pumpTypical characteristic curve of

rotodynamic & positive displacement pump

Pump Operating Point

The rate of flow at a certain head is called the duty point. The pump performance curve is made up of many duty points.

The pump operating point is determined by the intersection of the system curve and the pump curve

The Best Efficiency Point (BEP) is the pumping capacity at maximum impeller diameter, in other words, at which the efficiency of the pump is highest. All points to the right or left of the BEP have a lower efficiency

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Pump efficiency & diameter of pumpCombined pump & system curve

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Reynolds Number

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Head loses in straight pipe

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Head loses in fitting

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+

+ + =

+

+ +

+

Total Head Pompa (hp)

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Net Positive Suction Head

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Pump connected

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Contoh: Karakteristik Unjuk kerja pompa sentrifugal

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Selecting the right pump

Oversized pump

Requires flow control (throttle valve or by-pass line)

Provides additional head

System curve shifts to left

Pump efficiency is reduced

Solutions if pump already purchased

Variable Speed Drives or two-speed drives

Lower RPM

Smaller impeller

The Best Efficiency Point (BEP) is the pumping capacity at maximum impeller diameter, in other words, at which the efficiency of the pump is highest.

All points to the right or left of the BEP have a lower efficiency.

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DevelopedHead

ImpellerDiameter

Efficiency

Flow Rate

NPSH

Horsepower

http://capsicum.me.utexas.edu/ChE354/resources.html

Pump Performance Curves

Calculate the pipe loss in a 2 meter pipe with the diameter d=32 mm and a flow of Q = 10 m/h The pipe is made of galvanized steel with a roughness of 0.15, and the fluid is water at 20C.

ContohSoal 1

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ContohSoal 2

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Unit Penggerak Pompa

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Umumnya unit penggerak pompaterdiri dari 3 jenis penggerak

Motor bakar

Motor listrik

turbin

Yang menjadi pertimbangan dalam memilih penggerak pompa adalah

efisiensi tenaga pembangkit,

transmisi bahan bakar ke penggerak pompa,

mudah pemeliharaannya,

beaya bahan bakar,

modal,

flexibility,

independensi operasi, dan

pengawasan.

Penggerak tipe motor bakar danturbin sangat tidak ekonomis untukperencanaan pompa karenakonstruksinya berat, besar danmemerlukan system penunjangmisalnya pelumasan, pendinginan danpembuangan gas hasil pembakaran

Sistem penggerak motor listrik lebihsesuai dimana konstruksinya kecil dansederhanan sehingga dapatdigabungkan mejadi satu unit kesatuandalam rumah pompa

Dasar-dasar Pemilihan Pompa

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Didasarkan pada system ekonomisnya, yakni keuntungan dan kerugian jikapompa tersebut digunakan dan dapatmemenuhi kebutuhan pemindahanfluida sesuai dengan kondisi yang direncanakan.

Yang perlu diperhatikan dalampemilihan jenis pompa adalah fungsiterhadap instalasi pemipaan, kapasitas, head, viskositas, temperature kerja danjenis motor penggerak.

Kondisi yang diinginkan dalam perencanaan

Kapasitas dan head pompa harusmampu dipenuhi.

Fluida yang mengalir secarakontinu.

Pompa yang dipasang padakedudukan tetap.

Konstruksi sederhana

Menmpunyai effisiensi yang tinggi

Harga awal relative murah jugaperawatannya

Selection & Application of pump

Fluid Properties

pH, operating T, Solid Concentration, specific gravity, vapour P, viscosity,

End use requirement

Design pump capacity End use process

requirement Total system head

Environmental factor

Ambient T, humidity, operating P

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Pompa displasment Cairan atau gas dipindahkan dari pengisapan ke pengeluaran dengan variasi mekanis volume dari sebuah ruang atau beberapa ruang (chamber).

Pompa Sentrifugal Aliran melewati pompa disebabkan oleh gaya sentrifugal yang diberikan ke cairan dengan putaran sebuah impeller atau beberapa impeller.

Klasifikasi Pompa

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Pengeluaran berbandinglangsung dengan kecepatan

Pengeluaran sedikit berkurangsaat tekanan bertambah, biasanya akan lebih banyak slip pada fluida yang encer (less viscous)

Pompa dibuat dengan tekananpengeluaran sama denganhambatan yang muncul, mengabaikan kecepatan

Pompa ini adalah self priming

Displacement

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Screw pump

Rotary piston pump

Peristaltic pump

A vacuum is created by the rollers compressing the hose and moving along

Liquid is drawn into vacuum

Rollers capture liquid between them and move liquid towards discharge

Displacement - Rotary Pump

Vane pump

Not suitable for high viscosity products

Such liquids include LPG, ammonia, solvents, alcohol, fuel oils, gasoline, and refrigerants.

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Lope pump

Lobe pumps can handle solids.

A gentle pumping action minimizes product emulsification.

Can operate dry for brief periods of time.

Can handle viscous products

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External gear pumps (below) come in single or double configurations.

Handle viscous and watery-type liquids.

Reduced speeds with high-viscosity liquids results in greater efficiency.

Two gears come into and out of mesh to produce flow.

Uses two identical gears rotating against each other.

gear pump

For each revolution of an internal gear pump, (below) the gears have a fairly long time to come out of mesh allowing the spaces between gear teeth to completely fill and not cavitate.

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Displacement - Reciprocating Pump

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Piston, Plunger Pump

All reciprocating pumps (and some rotary pumps) depend on check valves (sometimes Known as non-return valves)

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Diaphragm pump

perfect sealing

high mechanical efficiency, since flexing a diaphragm involves much less friction then sliding a piston with seals up and down a cylinder

diaphragms need to be high quality rubber

a diaphragm pump is similar to a large diameter piston pump with a short stroke

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Dynamic pumps are used in conditions where high volumes required and a change in flow is not a problem.

As the discharge pressure on a dynamic pump is increased, the quantity of water pumped is reduced

Dynamic

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Pompa centrigugal berfungsi berfungsi mengubah energi (external driving force) ke energi kinetik di fluida dengan memberikan impuls ke fluida dengan bantuan impeller.

Sebuah difuser atau volute mengubah seluruh energi kinetik ke dalam tekanan atau dengan kata lain mesin ini menggunakan hukum dasar (Bernoulli) konversi energi potensial ke energi kinetik dan sebaliknya

Dalam hal kecepatan pompa konstran, maka:

Head bervariasi dengan kuadratdiameter

Kapasitas bervariasi dengandiameter

Power bervariasi dengan diameter pangkat tiga

Dalam hal kecepatan pompa adalah sebuah variabel, maka:

Head bervariasi dengan kecepatankuadrat

Kapasitas bervariasi langsungdengan kecepatan

Power bervariasi dengan kecepatanpangkat tiga, karena fungsi dari headdan kapasitas

Dynamic - Centrifugal Pump

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Electric Motor

Suction Nozzle

Discharge Nozzle

Bearing housing

Volute casing

Shaft

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Classification of impeller by flow

Radial impeller

Semi axial impeller

Axial propeller

Thicker the Impeller- More Water

Larger the DIAMETER - More Pressure

Increase the Speed - More Water and Pressure

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Gas lift pump Hydraulic Ram Pump

Dynamic - Special Effect Pump

Jet (Eductor) Pump Electromagnetic Pump

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Type, duties and capacities of centrifugal & displacement pump

Pump used in marine

shipboard applications

Diesel propulsion

vessel

Engine fresh water & sea water cooling pump

Single stage Centrifugal pump

Fuel oil transfer pumpsMultiple screw or rotary

pumps

Fuel oil supply & booster pumps

Multiple screw or gear pumps

Lubricating oil pumpsMultiple screw or gear

pumps

Ships service

Hydraulic System pumps Positive displacement pump

Bilge, ballast& Fire pumpsSingle stage centrifugal

pump

Hotel services

Single stage centrifugal pumps

Cargo

Single stage centrifugal pump

Multiple screw , lobe type rotary, sliding vane pump

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