All Types Pumps

8/10/2019 All Types Pumps

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PUMPS

OBJECTIVE: Understand the construction and operating principles of commonly used

pumps.

PUMP is device which adds to the energy of a liquid or gas causing an increase in itspressure and perhaps a movement of the fluid. There are many forms of energy, but

when pumps are being considered, use can be made of the energy equation as

follows.

A simple pumping system consists of a suction branch, a pump & a discharge branch.


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Pump

characteristics

Pump only adds to the energy of the fluid in the system. Energy

required to bring the fluid to the pump is an external one and in most

practical conditions is provided by the atmospheric pressure. .Reference to

the figure, even though liquid on suction side is below the pump center

line, still liquid will rise up to the pump center because of external

atmospheric pressure acting on surface of liquid; & no pressure acting on

other side (i.e. at pump center).


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Portable Positive Displacement pump (variable speed)

Suction

pipe

Discharge

pipe

Motor

Coupling

guard

Gearbox

Pump


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Marine pumps fall into two broad classes:

1. Displacement (self priming)

2. Dynamic

Displacement:Liquid or gas is displaced from suction to the discharge by the

mechanical variation of the volume of a chamber or chambers. Alldisplacement pumps are self-priming pumps. These

pumps include Reciprocating pump, Gear pump, and Screw pump.

Dynamic (Centrifugal pumps, Axial pumps) :

These dynamic pumps are basically radial flow or axial flow type.

Centrifugal pump: Flow through the pump is induced by the centrifugal

force imparted to the liquid by the rotation of an impeller or impellers.These pumps are not self-priming pumps and must be primed by gravity

supply or by priming equipment external or internal with the pump.


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Heart(Pump)
http://www.animatedsoftware.com./elearning/Engine%20of%20Life/eolife.swfhttp://www.animatedsoftware.com./elearning/Engine%20of%20Life/eolife.swf


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PISTON PUMP


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RECIPROCATING-PISTON PUMP (self priming)

(Single Acting piston Pump)


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If the level of liquid to be pumped is below the pump center line, the initial strokes of

bucket will draw out air (gas, in case liquid is volatile) from the suction pipe into

discharge pipe, creating a low pressure (vacuum) in the suction line. Liquid now risesinto suction pipeline under atmospheric pressure, (If the liquid is say water it will

theoretically rise up to 10.3 meter and hence pump can theoretically handle a suction

lift of 10.3 meter; However in real practice the pump can handle only upto 6 meter of

suction head) once liquid gets into the chamber, it will get discharged under pressure

through the discharge valve into discharge line. Pumping will continue in subsequent

upward strokes (it is therefore a self-priming pump).

Reciprocating motion of bucket

(piston) is obtained through a

connecting rod and crank

mechanism from an electric motor

drive or directly from a steamreciprocating engine. On downward

stroke suction valve lifts up against

spring and discharge valve remains

shut and upward travel discharge

valve against spring opens and

suction valve remains shut.


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RECIPROCATING-PISTON PUMP (self priming)

(Double Acting piston Pump)

Relief valve


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Double acting piston pump


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Double acting piston pump


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To get discharge of even flow we

utilize bottom water chamber

also by not keeping it open to

atmosphere; instead using this

chamber along with one moreset of suction and delivery valve

in similar way as explained for

top chamber. It is therefore

called a double acting pump;

which means that liquid is

discharged from both top andbottom side of the bucket.

Double Acting piston Pump

A relief valve is always fitted between the pump suction and dischargechambers as shown in the figure, to protect the pump, should it be operated with

closed discharge valve. Otherwise damage may occur to the pump being a

positive displacement pump. Further, an air vessel is provided, whose function

is to reduce the pressure fluctuations, which result from up an down strokes of

piston (bucket). This is illustrated in the above diagram.

Relief

valve


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Without Air vessel With Air vessel

Effect of providing air vessel at the discharge of a double acting


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Advantages of Reciprocating Pump

1. Ability to handle large portion of air, vapour or gas which enable them

to deal with volatile or hot liquids. Hence, these pumps are used as

cargo stripping pump for oil, chemical or gas tanker. Also used asboiler feed water pump.

2. As these pumps are self-priming and can handle high suction lifts, they

can be used effectively as priming pumps, engine room bilge pumps,

cargo hold bilge pumps or cargo stripper pumps.

Disadvantages of Reciprocating Pump

1. Construction is complicated due to presence of suction valve,

discharge valve, air vessels and relief valve. All positive displacement

pumps need a relief valve to prevent excess built up of pressure under

closure of delivery lines.


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This is a rotary displacement or rotary positive displacement pump. Two toothed

wheels, shown, mesh together and are a close fit in casing.. Initially the air or gas is

trapped between each pair of two consecutive teeth and same is dragged along the

casing from suction to discharge side till no more air is left on the suction side. Liquid

from the tank will thus rise up into suction line under atmospheric pressure.

Subsequently this liquid will now be trapped between each paid of two consecutive

teeth and dragged along the casing into discharge side and pumping of liquid will

commence. The working principle just explained is what makes the pump a self-

priming pump. Further if the liquid level on suction side is at a higher level, the liquid

will flow into suction side on its own at first instant itself.

Usually the pump is electric motor driven through a chain or wheel drive. Control

of flow rate is achieved by a by-pass valve or by controlling speed of prime-mover.

A number of such pumps in series can be used to due to develop high pressure.Such pumps are efficient (i.e very little losses) and smooth running.

These pumps are used for duties as a lube oil pump, boiler fuel oil pump, fuel oil

transfer pump, main engine driven lube oil pump. As a main Engine driven lube oil

pump it will have a set of suction and discharge valve to gave same side discharge

at all times irrespective of ahead or astern movement of the main engine.

GEAR PUMP


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GEAR PUMP OR GEAR WHEEL PUMP


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Gear Pump

Suction

Discharge


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Gear Pump (3 lobe)


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SCREW PUMP OR SCREW DISPLACEMENT PUMP

Two screws are driven in phase by timing gear. (Unlike gear pump where one

gear drives the other). This ensures that correct clearance is maintained at all

times between the screws, thereby preventing over heating and possible seizure.Pumping is effected by the two intermeshing screws rotating within a pump

casing. Each screw shaft has a right and a left-had screw, see figure

When the screws rotate, their close relation to each other creates pockets in

the helices; these pockets move axially and have the same effect as a piston

moving constantly in one direction.

The pump initially draws in air or gas (from volatile liquids) if liquid level is

below pump center, creates vacuum; liquid rises up under atmosphere pressure

filling pump casing.

Displacement or pumping takes place when the screws are further rotated

and liquid is drawn into the screws at the outer ends and pumped inwards to

discharge into the pump outlet.

Relief valve prevents built up of excessive pressure due to obstruction on

discharge line and thus protects the casing against possible damage.


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Double Screw Pump


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Construction

and working

of screwpump


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Advantages of screw pumps

Since pumps are self-priming and able to pump liquid and vapour

without loss of suction they are particular useful when draining tanks of

high vapour pressure liquids (Chemical / liquefied gases).

Pumps are well suited for tank draining and where fluid supply in

intermittent, such as may occur in lubricating oil supply to engines, with

the vessel rolling and pitching.

They are suitable for operation at high rotational speed (3500 rpm;1000 Lts /Min.) and can thus be driven by electric motor.

Can handle high viscosity (4000 centistrokes) find. Pumps are quiet,

smooth running and reliable.


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DYNAMIC PUMPS - CENTRIFUGAL PUMP


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CONSTRUCTION AND WORKING:

The pump consists of rotating impeller within a stationary casing. The impeller

construction has two discs joined at in between surface by a set of internal curved

vanes. Impeller has an eye (opening) at the center and is mounted on shaft, which

is driven by an electric motor, steam engine through crank mechanism or turbine, or

other prime mover.

Opening in the sides of the impeller near the shaft, called eye, communicates with

the suction branch as shown in figure

Assume there is a certain amount of fluid at the eye of the rotating impeller. Thefluid will flow radially outwards (because of centrifugal action) along the curved

vanes in the impeller, increasing its linear velocity.


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When the pump impeller rotates the fluid leaves the impeller. The high velocity fluid

is collected in specially shaped casing (volute casing), where some of the

kinetic energy of the fluid is converted into pressure energy. Fluid under

pressure now leaves the impeller producing a drop in pressure behind it at the

eye of the impeller. This causes fluid from the suction pipe to flow into pump

under atmospheric pressure. However, if initially there is not liquid at the eye,

there will be no pumping action as explained.

Centrifugal pump therefore is not a self-priming pump. In such case, where

normally at start of the pump the level of the liquid is below the eye of the

centrifugal pump, we have to prime the pump.


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Centrifugal pumps

Vertical pump

Horizontal pump

Suction

Discharge

Discharge

Impeller


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Impeller


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Prime the pump: Use an air pump initially to draw out air from the suction branch &


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Prime the pump: Use an air pump initially to draw out air from the suction branch &

thus make liquid rise to the eye under atmospheric pressure.

Eg: Emergency fire pump. Bilge and ballast pump.

BILGE AND BALLAST PUMP

In absence of liquid, air (sometimes also vapour) will be present at the eye, and

owing to its light density air could be thrown out under centrifugal force only if rpm of

the impeller is very high (Turbo charger blower).


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Automatic arrangement for pumping out bilges, using a centrifugal pump is shown

above, where the air (vane) pump will get engaged automatically and draw out any

air at the start or during running. Once air is drawn out it will get disengaged

automatically.


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In case of pumping out engine room bilges using a centrifugal pumpwe

can prime the pump by initially drawing in water from outside sea, level of

which is higher. Once water runs into the eye of rotating impeller, the suctionbranch of pump can be switched over from sea to engine room bilges and

pumping out of bilges can now commence.


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Similar (previous) method can be used when stripping a cargo tank. Initial

liquid can be drawn from an oil tank, level of which is higher than the pump.

Performance Characteristic Curves of a Centrifugal Pump


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Performance Characteristic Curves of a Centrifugal Pump

From above it is clear

I. That if the pump discharge head is lesser the flow rate of liquid is

higher and therefore pumping of liquid is faster.

Pump if run at normal duty flow rate by maintaining normal duty discharge

head the liquid will be pumped utilizing least possible rate of energy by the

pump (at this point of the pump is maximum).

NPSH


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This stand for net Positive Suction Head. If the pressure exerted by atmospheric air ( or

any other atmosphere which is surrounding the liquid on suction side) is H0 and is more

than the three losses mentioned below :

Loss of head because of friction in the suction line H1.

+

Loss of head because of volatility of liquid H2.+

Loss of head in raising the liquid to the pump suction H3.

Only then will the liquid rise up to the pump. However the liquid can be discharged

effectively and without cavitations of the pump only if this left over head called

available NPSH is greater than the required NPSH provided by the pump manufacturer.

CAVITATION


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CAVITATION

This process of the formation and subsequent collapse of vapor bubbles in a pump is

called cavitation.Cavitation causes

1. Degrades the performance of a pump - fluctuating flow rate and discharge pr.

2. Destructive to pumps internal components.- When a pump cavitates, vapor bubbles form in the low-pressure region directly

behind the rotating impeller vanes. These vapor bubbles then move toward the

oncoming impeller vane, where they collapse and cause a physical shock to the

leading edge of the impeller vane. This physical shock creates small pits on the

leading edge of the impeller vane. Each individual pit is microscopic in size, but

the cumulative effect of millions of these pits formed over a period of hours ordays can literally destroy a pump impeller.

3. Excessive pump vibration.

Vibration could damage pump bearings, wearing rings, and seals.

Noise is one of the indications that a centrifugal pump is cavitating.

A cavitating pump can sound like a can of marbles being shaken. Other indicationsthat can be observed from a remote operating station are fluctuating discharge

pressure, flow rate, and pump motor current.


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Cavitation damage to propeller

AXIAL FLOW PUMP or STRAIGHT FLOW or PROPELLER PUMP
http://upload.wikimedia.org/wikipedia/en/e/e6/Cavitation_Propeller_Damage.JPG


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Axial flow pump is one in which

a screw propeller is used to

create an increase in pressure

by causing an axial

acceleration of liquid. Thevelocity increase is then

converted into pressure by

suitably shaped outlet passage

and guide vanes. Pump works

similar to an idea of a propeller

working in a closed duct.

When conditions like large

capacity and relatively low

discharge head of upto 12 m

have to be met, a horizontal or

vertically arranged axial pumpis most suitable.

These pumps are used as sw circulating pumps for main condenser, which

flow rate has to be large and discharge head to be low (as pumping is from

sea to sea). Also used for the duties of heeling and trimming of ships. This is

again because the pump is of reversible flow and high through-put type.


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Diaphragm pump


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Double Acting Diaphragm

pump(Weldon)

M lti t C t if l


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Multistage Centrifugal pump


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Duplex pump


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Axial piston pump
http://www.animatedsoftware.com/pumpglos/wobble.htm


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Radial piston pump


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DUTCH PUMP


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VANE PUMP

R t VANE P


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Rotary VANE Pump


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1) Piston Block
http://www.animatedsoftware.com/pics/pumps/hugedeep.gif


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2) Cylinder Drum

3) Piston Shaft

4) Five degree angled

control surface

5) End Plate

6 & 7) Ports8) Drive Shaft

9) Piston Head

1) Piston Block

2) Cylinder Drum

3) Piston Shaft

4) Five degree angled

control surface

5) End Plate

6 & 7) Ports

8) Drive Shaft

9) Piston Head


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All Types Pumps

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