Pumps
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- Pages: 26
PUMPS Prepared by
Md.Shamsuzzaman
Lesson Overview Lesson covers the type of pumps commonly installed on board ships, their constructions, working principles, characteristics, safety operation.
28/11/09
2
Learning Objectives
Definition of Pump Classification of Pumps Working principles of positive displacement pumps Construction features of positive displacement pumps Working principles of rotordynamic pumps Construction features of rotordynamic pumps Characteristics of pumps Safe operation of pumps
28/11/09
3
Tutorial 1. State the classification of pumps used for shipboard application. 2. With the aid of a labelled sketch, briefly explain the working principle of a typical i) reciprocating pump ii) gear pump iii) vane pump
Iv) centrifugal pump
28/11/09
4
Tutorial 4.
5.
6.
Draw the pump performance (H-Q) curve for the centrifugal pump Explain how suction condition of the pump may be improved Explain the cause of efficiency drop in centrifugal pump.
28/11/09
5
Tutorial 7.
8.
Briefly explain the differences between positive displacement and rotodynamic pumps. With reference to the operation of a pump, explain the terms ‘self-priming’ and ‘non-self priming’.
28/11/09
6
Definition Pump is a device that imparts energy to a fluid passing through it to enable the fluid to move from one point to another. In practice, pumps change both the velocity and the pressure passing through them. 28/11/09
7
Energy Flow in Pumping System Pump losses Kinetic energy At Suction
+ Pressure energy At Suction
Kinetic energy At Discharge
+
Pump
Pressure energy At Discharge Energy flow from prime mover
28/11/09
8
Types of Pumps Marine Pumps fall into two broad classes:
Positive Displacement Pumps
Rotordynamic Pumps
28/11/09
9
Positive Displacement Pumps Working Principles:
Fluid is displaced from the suction to the discharge by the mechanical variation of the volume of chamber or chambers at every stroke or rotation of the pump
Volume of pump chamber alternately increases to draw the liquid in from suction pipe & then decreased to force the liquid out into the delivery pipe
This may be done by either a reciprocating motion of a piston or by a rotary motion of specially designed vanes, gears or screws
28/11/09
10
Positive Displacement Pumps Characteristic
Self-priming
All the valves at the discharge side of the pumps must be kept open prior starting
Failure to do so will cause rapid increase of fluid pressure, leading to failure at the weakest point in the system
Relief valve is always fitted in the system to avoid such failure
28/11/09
11
Positive Displacement Pumps Subdivided into Two main categories:
Reciprocating Pumps - where plunger or piston is reciprocated in a fluid cylinder - suitable for delivering small quantities at high pressure
Rotary Pumps ( Gear, Screw, Vane pumps ) - where the liquid is forced through the pump casing by means of screws, gears or vanes - used for delivering moderate quantity at moderate pressure
28/11/09
12
Reciprocating Pump Main Components
Cylinder Piston Piston rod Gland Suction valve Discharge valve
Pump may be of Single acting or Double acting type
28/11/09
13
Single Acting Reciprocating Pump
There is one suction & one discharge per cycle
Piston moves down during suction stroke
Causes low pressure to create & fluid to flow into cylinder by opening suction valve
Piston moves up during discharge stroke
Causes fluid to be compressed and pressurised
Discharge takes place by opening discharge v/v by high pressure fluid
SUCTION STROKE
28/11/09
DISCH STROKE
14
Double Acting Reciprocating Pump
There is two suction & two discharge per cycle
Piston moves from left to right (one stroke)
Piston compresses fluid above piston (discharge)
Piston draws fluid below piston (suction)
28/11/09
15
Pressure Pulsation
Pressure pulsations are inherent problem in reciprocating pump It causes pipes to surge & vibrate
Pipes may become loose and break under heavy strain
Accumulators are used to reduce the impact of pressure surges
28/11/09
C
B
A
C
B
Pressure
A
Str
16
Accumulators
Accumulators are air vessels or spring loaded device
Absorbs some energy during the pump discharge stroke
Releases this energy during low pressure period and raises the pressure in the pipe
Thus reduces the pressure pulsation by avoiding sharp drop in pressure
28/11/09
17
Gear Pump
It is a positive displacement pump
It consists of two meshing gears with one driving the other
Fluid flows between the casing and the gear teeth
Commonly employed for lube & fuel oil transfer
Must have relief valve installed in the system
28/11/09
18
Screw Pump
Screw pumps are positive displacement pumps
Screws are meshed together with one driving other
Fluid is displaced through the recesses between the screws and the casing
May have single, double or triple screws
28/11/09
19
Vane Pump
Vane pumps are positive displacement pumps
Rotors having slots for vanes
Centre of rotor is eccentric with casing
This causes vanes to move in and out as the rotor rotates
Causes change in volume in the respective chamber, similar to reciprocating pump
28/11/09
20
Rotodynamic Pumps
Often Known as dynamic pumps or centrifugal pumps
Centrifugal pumps are more suitable for delivery of large quantities at low discharge pressure
Are Non-self priming pumps
Looses suction and unable to pump once air gets into the pump system Must be primed before starting
Used on ship as G.S. pump, Ballast Pump, S.W. & F.W. cooling pumps
28/11/09
21
Centrifugal Pump Main Components
Impeller Impeller wear ring Volute Casing Shaft Ball bearing Gland
28/11/09
22
Centrifugal Pump Working Principle
Impeller rotates at high speed
Fluid enters through the ‘eye’ of the impeller
Fluid is thrown by centrifugal force from the centre (suction side) radially outwards to the periphery of impeller (discharge side)
High velocity fluid enters the stationary volute casing
Volute casing converts the kinetic energy of fluid into pressure energy at the discharge of the pump
28/11/09
23
Centrifugal Pump Impeller Wear Ring
Located on the casing at the impeller suction
Must have clearance to allow rotation of impeller
If clearance is too small, wear ring may come in contact with impeller due to misalignment, expansion
If clearance is too big, fluid flows back to suction side
Cause drop in discharge pressure & pump efficiency
28/11/09
24
Centrifugal Pump
Curve A shows the pump capacity, given in terms of flow rate (normally M3/hr), as a function of the head developed by the pump, given in terms of meters liquid column (mIc). This curve is called the pump characteristic.
28/11/09
25
Centrifugal Pump
Curve B shows the Net Positive Suction Head (NPSH) requirement for the pump as a function of flow‑rate.The NPSH requirement at any flow rate is the positive head of fluid required at the pump suction over and above the cargo's vapour pressure to prevent cavitation at the impeller. 28/11/09
26
Md.Shamsuzzaman
Lesson Overview Lesson covers the type of pumps commonly installed on board ships, their constructions, working principles, characteristics, safety operation.
28/11/09
2
Learning Objectives
Definition of Pump Classification of Pumps Working principles of positive displacement pumps Construction features of positive displacement pumps Working principles of rotordynamic pumps Construction features of rotordynamic pumps Characteristics of pumps Safe operation of pumps
28/11/09
3
Tutorial 1. State the classification of pumps used for shipboard application. 2. With the aid of a labelled sketch, briefly explain the working principle of a typical i) reciprocating pump ii) gear pump iii) vane pump
Iv) centrifugal pump
28/11/09
4
Tutorial 4.
5.
6.
Draw the pump performance (H-Q) curve for the centrifugal pump Explain how suction condition of the pump may be improved Explain the cause of efficiency drop in centrifugal pump.
28/11/09
5
Tutorial 7.
8.
Briefly explain the differences between positive displacement and rotodynamic pumps. With reference to the operation of a pump, explain the terms ‘self-priming’ and ‘non-self priming’.
28/11/09
6
Definition Pump is a device that imparts energy to a fluid passing through it to enable the fluid to move from one point to another. In practice, pumps change both the velocity and the pressure passing through them. 28/11/09
7
Energy Flow in Pumping System Pump losses Kinetic energy At Suction
+ Pressure energy At Suction
Kinetic energy At Discharge
+
Pump
Pressure energy At Discharge Energy flow from prime mover
28/11/09
8
Types of Pumps Marine Pumps fall into two broad classes:
Positive Displacement Pumps
Rotordynamic Pumps
28/11/09
9
Positive Displacement Pumps Working Principles:
Fluid is displaced from the suction to the discharge by the mechanical variation of the volume of chamber or chambers at every stroke or rotation of the pump
Volume of pump chamber alternately increases to draw the liquid in from suction pipe & then decreased to force the liquid out into the delivery pipe
This may be done by either a reciprocating motion of a piston or by a rotary motion of specially designed vanes, gears or screws
28/11/09
10
Positive Displacement Pumps Characteristic
Self-priming
All the valves at the discharge side of the pumps must be kept open prior starting
Failure to do so will cause rapid increase of fluid pressure, leading to failure at the weakest point in the system
Relief valve is always fitted in the system to avoid such failure
28/11/09
11
Positive Displacement Pumps Subdivided into Two main categories:
Reciprocating Pumps - where plunger or piston is reciprocated in a fluid cylinder - suitable for delivering small quantities at high pressure
Rotary Pumps ( Gear, Screw, Vane pumps ) - where the liquid is forced through the pump casing by means of screws, gears or vanes - used for delivering moderate quantity at moderate pressure
28/11/09
12
Reciprocating Pump Main Components
Cylinder Piston Piston rod Gland Suction valve Discharge valve
Pump may be of Single acting or Double acting type
28/11/09
13
Single Acting Reciprocating Pump
There is one suction & one discharge per cycle
Piston moves down during suction stroke
Causes low pressure to create & fluid to flow into cylinder by opening suction valve
Piston moves up during discharge stroke
Causes fluid to be compressed and pressurised
Discharge takes place by opening discharge v/v by high pressure fluid
SUCTION STROKE
28/11/09
DISCH STROKE
14
Double Acting Reciprocating Pump
There is two suction & two discharge per cycle
Piston moves from left to right (one stroke)
Piston compresses fluid above piston (discharge)
Piston draws fluid below piston (suction)
28/11/09
15
Pressure Pulsation
Pressure pulsations are inherent problem in reciprocating pump It causes pipes to surge & vibrate
Pipes may become loose and break under heavy strain
Accumulators are used to reduce the impact of pressure surges
28/11/09
C
B
A
C
B
Pressure
A
Str
16
Accumulators
Accumulators are air vessels or spring loaded device
Absorbs some energy during the pump discharge stroke
Releases this energy during low pressure period and raises the pressure in the pipe
Thus reduces the pressure pulsation by avoiding sharp drop in pressure
28/11/09
17
Gear Pump
It is a positive displacement pump
It consists of two meshing gears with one driving the other
Fluid flows between the casing and the gear teeth
Commonly employed for lube & fuel oil transfer
Must have relief valve installed in the system
28/11/09
18
Screw Pump
Screw pumps are positive displacement pumps
Screws are meshed together with one driving other
Fluid is displaced through the recesses between the screws and the casing
May have single, double or triple screws
28/11/09
19
Vane Pump
Vane pumps are positive displacement pumps
Rotors having slots for vanes
Centre of rotor is eccentric with casing
This causes vanes to move in and out as the rotor rotates
Causes change in volume in the respective chamber, similar to reciprocating pump
28/11/09
20
Rotodynamic Pumps
Often Known as dynamic pumps or centrifugal pumps
Centrifugal pumps are more suitable for delivery of large quantities at low discharge pressure
Are Non-self priming pumps
Looses suction and unable to pump once air gets into the pump system Must be primed before starting
Used on ship as G.S. pump, Ballast Pump, S.W. & F.W. cooling pumps
28/11/09
21
Centrifugal Pump Main Components
Impeller Impeller wear ring Volute Casing Shaft Ball bearing Gland
28/11/09
22
Centrifugal Pump Working Principle
Impeller rotates at high speed
Fluid enters through the ‘eye’ of the impeller
Fluid is thrown by centrifugal force from the centre (suction side) radially outwards to the periphery of impeller (discharge side)
High velocity fluid enters the stationary volute casing
Volute casing converts the kinetic energy of fluid into pressure energy at the discharge of the pump
28/11/09
23
Centrifugal Pump Impeller Wear Ring
Located on the casing at the impeller suction
Must have clearance to allow rotation of impeller
If clearance is too small, wear ring may come in contact with impeller due to misalignment, expansion
If clearance is too big, fluid flows back to suction side
Cause drop in discharge pressure & pump efficiency
28/11/09
24
Centrifugal Pump
Curve A shows the pump capacity, given in terms of flow rate (normally M3/hr), as a function of the head developed by the pump, given in terms of meters liquid column (mIc). This curve is called the pump characteristic.
28/11/09
25
Centrifugal Pump
Curve B shows the Net Positive Suction Head (NPSH) requirement for the pump as a function of flow‑rate.The NPSH requirement at any flow rate is the positive head of fluid required at the pump suction over and above the cargo's vapour pressure to prevent cavitation at the impeller. 28/11/09
26
