Pumps used onboard

What Do You Mean By A Pump?
A Pump Is A Device That Transfers Energy To A Fluid Passing Through It. In Practice, Pumps Change Both The Velocity And The Pressure Of The Fluid Passing Through It, The Ratio Of These Energy Changes Depends Upon The Type And The Speed Of The Pump In Use. 

What Are The Main Types Of Pumps?
Main Types Of Pumps
1. Displacement Pumps
2. Kinetic Pumps

What Do You Mean By Displacement Pump? Also Briefly Explain Types Of Displacement Pump.
1. Displacement Pumps
In Displacement Pumps The Volume Of The Pump Chamber Is Alternately Increased To Draw The Liquid In (suction) And Then Decreased To Force The Liquid Out (delivery). This Is Done By A Reciprocating Motion Of A Piston Or Plunger Within A Cylinder, Or By A Rotary Motion Of Specially Designed Vanes, Gears Or Rotors. 
Positive Displacement Are Provided Fitted With Relief Valve Safeguard The System

Types Of Displacement Pump?
i) Reciprocating Pump: A Reciprocating Pump Has 'to And Fro' Motion Provided By A Direct Acting Steam Driven Piston, Or Through Mechanisms That  convent Rotary Motion To Reciprocating Motion (e.g. Cranks, Eccentrics Etc.).Due To Fluctuating Motion Of The Piston, The Delivery And Pressure Is Not Steady. To Improve The Overall Performance, The Pump Is Arranged As Double Acting And Fitted With An Accumulator (air Vessel) On The Discharge Side Of The Pump To Achieve A Near Steady Pressure. 
Reciprocating Type Pumps Are Suitable For Delivering Smaller Quantities Of Liquids At High Pressures. They Are Self-priming And Can Handle High Suction Lifts. However Their Construction Is Complicated And Uneconomical Except For Limited Applications E.g. Bilge Pumps, Stripping Pumps, Etc.

ii) Rotary Pumps
 Rotary Types Of Displacement Pumps Are Commonly Used On Board Ships In Place Of Reciprocating Pumps.
A Rotary Pump Continuously Scoops The Fluid From The Pump Chamber By Means Of Gears Or Screws, Or Vanes Etc. When Rotated, Liquid Gets Trapped In Small Pockets Created By The Moving Element And It Gets Transferred From The Suction Side To The Delivery Side.

Types Of Rotary Pumps

a) A Gear Pump Has Intermeshing Gears Or Lobed Members Enclosed In A Suitably Shaped Housing. The Efficient Of These Pumps Depends Upon The Accuracy With Which The Component Parts Are Machined And Fitted I.e. Working Clearances. Gear Pump Is The Simplest Type Of Positive Delivery Pumps And Most Commonly Used On Board Ship For Handling Small Quantities Of Fluids -usually Oils, E.g. Lubricating Oil Transfer Pumps, Auxiliary Diesel Engine Lubricating Oil Pump, Oil Separator Pumps Etc. Delivery Rate Depends Directly Upon The Speed Of The Pump. 

B) A Lobe-pump Like A Gear Pump And Was The Earlier Type Of Mechanical Pumps Used For Supercharging Of Main Engine. Now You Will Find It Being Used A Sewage Pump.


C) A Vane Type Pump Operation Is Also Based On The Principle Of Increasing The Size Of The Cavity To Form A Vacuum, Allowing The Space To Fill With The Incoming Liquid, And Then Forcing The Fluid Out Of The Pump Under, Pressure By Diminishing The Volume.

        The Sliding Vanes Or Blades Fit Into The Slots In The Rotor. Ahead Of The Slots And In The Direction Of Rotation, Grooves Admit The Liquid Being Pumped By The Vanes, Moving Them Outward With A Force Of 'locking Pressure That Varies Directly With The Pressure That The Pump Is Operating Against. The Grooves Also Serve To Break The Vacuum On The Admission Side. The Operating Cycle And The Action Of Centrifugal Force And Hydraulic Pressure Hold The Vanes In Contact With The Casing. 
       This Type Of Pumps Are Most Suitable For Variable Displacement Requirement E .g. Hydraulic Steering System, Hydraulic Winches Etc. 

iii) Screw Pump: It Is Most Suitable For Viscous Fluids And Is Commonly Used For Medium To Heavy Duty Requirements. (e.g. Main Engine Lubricating Oil Pump, Cargo Pumps, Oil Transfer Pumps Etc.  Screw Pumps Are Broadly Classified By The Number Of Screw Rotors Employed E.g.   

Types Of Screw Pump
a) Single-screw- Rotating Within A Accurately Bored Cylinder -mono-pumps As Commonly Known For Marine Application Has One Power Rotor Within A Semi-flexible Stator, And This Type Can Handle Highly Abrasive Liquids And Can Also Pump Liquids Containing Fairly Large Solid Particles.
b) Two-screw- Either With Intermeshing Contact, Or Separately Driven And Synchronised To Run With Positive Clearance.  
C) Three-screw -with Three Screw On Parallel Axis. The Central Screw Is Power Driven And Drives Two Outer Idler Screws. The Assembly Of Three Screws Is Usually Supplied In A Single Element.     

What Do You Mean By Kinetic Pumps (Roto-dynamic)?
Centrifugal Pumps Are Most Common Type Of Pumps On Board Ships. Almost All Of The Pumps On Board For Seawater Or Fresh Water Are Of Centrifugal Type. They Come In Various Sizes And Arrangements Of Flow And Stages And Design Of Impellers And Casings.
Flow: Radial, Mixed, Or Axial 
Stage: Single Stage, Multiple Stage
Impellers: Open Or Closed Impellers
Drive: Horizontal Or Vertical Drive.
On Some Ships, Even The Main Engine Lubricating Oil Pump Is Of Vertical Centrifugal Type Located Within The Oil Sump And Driven By Electric Motor Above The Tank Top. These Pumps Are Called Submersed Type Pumps.

Explain Operating Procedures For Displacement Pumps?
Starting:  
Precaution: Never Start A Displacement Pump Without Ensuring That All Valves On The Discharge Line Are Open.  
1. Attempt To Turn The Pump Shaft Manually To Ensure It Is Not Seized.  
2. Ensure That The Cocks To The Pressure Gauges Are In Line For Indicating The Pressure And Not Open To The Atmosphere.  
3. Open Appropriate Valves On The Discharge Side Where The Liquid Has To Go. 
4. Open Appropriate Valves On The Suction Side. 
5. When Provided With A Manually Controlled Valve (bypass) To Regulate Pressure, Release The Spring Load To Start The Pump At A Reduced Load. 
6. Start The Pump And Observe For Abnormal Sounds, Load On The Motor, Or Excessive Pressure Build Up. (stop The Pump Immediately In Case Of Any Abnormality) 
7. If The Liquid Being Drawn Is From A Distant Tank Below The Level Of The Pump, The Pump Will Take Some Time To Draw The Liquid. There Will Be A Change In The Running Sound When The Liquid Reaches The Pump. If The Liquid Is Cold The Pump Is Likely To Vibrate And Cause An Abnormal Noise.  
8. Observe Pressure As The Pump Picks Up Liquid. Adjust Pressure Regulating Valve To Increase The Discharge Pressure To Normal. Observe Leakages At Pump Gland, Valves, And Along The Pipeline. 
9. Incase The Pump Is Having Difficulty In Drawing The Liquid. Stop The Pump And Check Suction Filter. Clean If Necessary. Heat The Liquid In Tank If The Temperature Is Low. 

Stopping The Pump: 
1. Stop The Motor. 
2. Shut All Valves On The Suction And Discharge Side. 
3. Open Bypass Valve. 
4. Clean The Suction Filter If The Pump Has Drawn Oil From Dirty Tank Or The Last Part Of Oil Tank.  
5. Record Operating Time, Pressure, Tank Levels As Per Standing Instructions On Board.

Explain The Operation Of Centrifugal Pump?
All Types Of Centrifugal Pumps Depend On Centrifugal Force For Their Operation. Centrifugal Force Acts On A Body Moving In A Circular Path, Tending To Force It Away From The Axis Of Rotation. In The Centrifugal Pump, Vanes Or Impellers Rotating Inside A Close Fitting Housing Draw The Liquid Into The Pump Through The Central Inlet Opening, And By Means Of Centrifugal Force The Liquid Is Thrown Outward Through A Discharge Outlet At The Periphery Of The Housing. The Vacuum Created Thereby Draws Water Into The Casing Through The Inlet Opening. The Process Continues As Long As The Motion Is Provided To The Rotor And As Long As Supply Of Liquid Is Available. In The First Practical Centrifugal Pump, The Rotor (impeller) Was Built With Straight (radial) Vanes. Curved Vanes Were Introduced In Later Type Of Pumps Having Curved Casing With A Volute & Such Pumps Are Called Volute Pumps. (Definition: The Volute Type Casing Or Housing Form A Progressively Expanding Passageway Into Which The Impeller Discharges The Water.)
       The Head At Which A Centrifugal Pump Can Operate Effectively  is Limited. The Double Admission Can Be Adopted For Higher Heads. Great Advantage Of Double - Admission Type Of Pump Is That The Impeller Is Balanced Hydraulically In Axial Direction.

What Are The Main Advantages Of Multistage Pump Over Single Stage Pump?
Single Stage Pumps Are Suitable For Low To Moderate Head. For Higher Heads, Multi-stage Pumps Are Used. In A Multi-stage Pump, The First Stage Receives The Water Directly From The Source Through The Admission Pipe, Builds The Pressure Up To The Correct Single-stage Pressure And Passes It To The Next Stage Where The Pressure Is Further Increased Until The Fluid Is Delivered From The Final Stage As Desired. 

What Are The Major Components Of Centrifugal Pumps?
Major Components Of A Centrifugal Pump Are:
I) Casing Or Housing, 
Ii) Impeller And Wearing Rings 
Iii) Stuffing Box Assembly 
Iv) Bearing And 
V) Drive Shaft. 
        Pump Casing Is Cast And For A Vertical Pump Is Usually Split Axially. For Horizontal Pump The Casing Is Either Split Diagonal Or Built Up Of Radial Pieces, Which Are Assembled On A Shaft In Sequence. The Volute-shaped Housing Is Proportioned To Produce Equal Flow Velocity Around The Circumference And To Reduce Gradually The Velocity Of The Liquid As It Flows From The Impeller To The Discharge Outlet. The Objective Of This Arrangement Is To Change Velocity Head To Pressure Head. Single Or Multi-stage Pumps May Have Single Admission Or Double Admission. The Chief Disadvantage Of The Single-admission Pump Is That The Casing Provides Inlet And Delivery Passages And Accommodates Guides For Impeller And Shaft (bearing And Wear Rings). Casing Also Acts As A Support For Parts And Provides Stuffing Box For A Shaft Seal Or A Gland. The Choice Of Material For Casing And Other Parts Of The Pump Depend Upon The Fluid Passing Through The Pump, (sea Water, Fresh Water, Oils, Acid Etc. And Whether Hot Or Cold). Cost Is An Important Factor In The Choice Of Materials Keeping In Mind The Reliability. Impellers Govern The Efficiency Of The Pump. They Are Designed To Meet A Given Set Of Operating Conditions. The Number Of Vanes In Impeller Vary From One To Eight Or More Depending Upon The Type Of Service, Size Etc. Impellers Are Sub Classified As:
1) Open Type, 
2) Semi-open Type And The 
3) Enclosed Or Shrouded Type As Shown Below. Enclosed Impellers Are Most Efficient.

Explain Operating Procedures For A Centrifugal Pump?
Starting:     
1. Open The Suction Valve Completely. Keep The Discharge Valve Closed At This Stage,
2. Open The Air Vent And If The Water Comes Out From It, Close It (pump Is Full Of Water And Is In 'primed' State).
3. If The Pump Is Of The Self-priming Type With An Attached Vacuum Pump, Keep The Air Vent Closed And Open The Check Valve On The Vacuum Pump Line.
4. Start The Motor (pump)
5. When The Discharge Pressure Has Risen, Open The Discharge Valve Gradually. (For A Self-priming Arrangement, Close The Check Valve Connecting To The Vacuum Pump.)
6. Changeover Suction And Discharge As Required Gradually.
7. Monitor Suction And Discharge Pressures, Load On The Motor, Vibrations, And Leakages Through Valves And Glands. If Necessary 'nip Up' The Gland.

Starting The Pump With Closed Discharge Valve Reduces The Starting Current On The Motor And Prevents Damage To The Pump Parts. Since Centrifugal Pump Is Not A Positive Displacement Type, There Is No Danger Of Build Up Of Excessive Pressure. Pump Casing And Parts Have Been Designed To Withstand Maximum Pressure The Pump Can Produce In This Case.
In Case The Pump Looses Suction, Prime It As Soon As Possible. Avoid Running The Pump Without Liquid Even For Short Periods To Minimise Wear Between The Impeller And Its Guide Ring (wearing Ring).

Stopping The Pump:
1. Incase Of A Pumps Used For Bilge Or Ballast Line, Before Stopping The Pump, Run The Pump 'sea To Sea' For Some Time To Flush The Pump And The Pipe Line Of Contaminated Water.
2. Close The Discharge Valve
3. Stop The Motor
4. Close Suction Valves And All Other Valves That Were Opened For Use. 
Record Starting And Stopping Times As Per Ship Board Instructions And Practices.