pumps course material

Positive displacement

pumps

Centrifugal Pumps

LowHighRotational

speed

HugeSmallSize

Valves

More maintenance

No valves

Less maintenance

Maintenance

The same flow rate at the

same rotational speed

regardless pressure value

Depend on Pressure and

the rotational Speed

Flow rate

Safety valve is necessaryNo need for safety valvePressure

No need for primingPriming is necessaryOperation

Pumps enable a liquid to:

1. Flow from a region or low pressure to one of high pressure.

2. Flow from a low level to a higher level.

3. Flow at a faster rate.

1. Negative displacement, hydrodynamic,

pumps:

This type is generally used for low-pressure, high-volume flow applications.

Normally their maximum pressure capacity is limited to 17- 20 bar (250-300 psi).

This type of pump is primarily used for transporting fluids from one location to another.

These pumps may be further subdivided into several varieties of centrifugal and other special-effect pumps.

2. Positive displacement, hydrostatic,

pumps (cont.)

These pumps have the following advantages over negative displacement pumps:-

High-pressure capability up to 680 bar (10,000 psi) or higher.

Small and compact size.

High volumetric efficiency.

Small changes in efficiency throughout the design pressure range.

Great flexibility of performance (can operate over a wide range of pressure requirements and speed ranges).

There are three main types of positive displacement pumps namely, gear, vane and piston.

Centrifugal pumps

Advantages of centrifugal pumps

Cheap

Simple design

Quite operation

Continuous flow without pulsation

Low maintenance cost

Working Mechanism of Centrifugal

Pump

Working Mechanism of a Centrifugal

Pump

Centrifugal pump components

1)Stationary elements :

Casing

Shaft Seal

2) Rotating elements :

Impellers

Shaft

PUMP SHAFT

BEARINGS IMPELLER

AS THE PUMP SHAFT ROTATES

A LIQUID IS SUPPLIED TO THE

CENTRIFUGAL FORCE EXPELS THE

LIQUID OUT FROM THE IMPELLER

Casing

The Casing generally are two types:

I. Circular casing (for low head)

II. Volute casing (for high head)

I. Volute casing

A volute is a curved

funnel increasing in

area that converting

the kinetic energy

from the liquid

discharged from the

impeller to a

pressure energy.

Casing

II. Circular casing

have stationary

diffusion vanes

surrounding the

impeller periphery

that convert kinetic

energy to pressure

energy.

Casing

Casing

The Casing also can be divided into:

Solid casing : is one casting or fabricated

piece.

Split casing : consists of two or more parts are

fastened together.

Casing

Horizontally split or axially

split casing.

Vertically split or radially split casing.

Suction and Discharge Nozzles

End suction/top discharge nozzles

Top suction Top discharge nozzles

Side suction / Side discharge nozzles


I- Top suction/Top discharge


II- End suction/Top discharge


III- Side suction/Side discharge

Shaft seals

There are two basic kinds of shaft seals:

Compression packing.

mechanical seals.

Pump manufacturers use various design techniques to

reduce the pressure of the product trying to escape such

the addition of balance holes through the impeller to

permit most of the pressure to escape into the suction side

of the impeller.

Why do we need a seal?

Old Style Sealing Using Packing

Shaft seals

1. Packing

Advantages of Gland Packing

Inexpensive sealing medium

Many different types available

Established sealing medium (familiarity)

Ease of temporary repair

Considered easy to use / install

Disadvantages of Gland Packing

Must leak to work effectively

Runs on shaft/sleeve causing Wear

Friction

Parasitic power loss

Requires regular adjustment

productivity goals, is this such a good solution?

Mechanical seals

Three Sealing Concerns

Basic Parts

Rotating Sealface (1)

Stationary sealface (3)

Secondary sealing

elements (2+4)

Spring element (5)

Torque transmission (6)

4 3 1 2 5 6

Rotating faces

Solid faces

Inserted faces

FACE FLATNESS

This illustration shows a face

being inspected on an Optical

Flat.

Take notice of the light bands

that are visible on the reflection

of the face.

Laying a straight edge on a

tangent to the inside

circumference of the face, how

many light bands are crossed?

0-rings: location and compression

Dynamic 0-ring

Stationary 0-ring

Stationary 0-ring

Dynamic 0-ring

Springs

helical springs

wave springs

metal bellows

Single spring / Multiple spring designs

The seal has one big spring to push the face against the stationary seat

Multiple spring seals have a number of springs to push the face

Springs

acceptable minimal Leakage

Shaft Leakage

0 psi

25 psi

50 psi

Liquid

Liquid + Vapor

Vapor + Liquid

Vapor

Pressure Drop & Vaporization

100 psi

high temperature

media

Boiling point

Frictional heat

The sealing gap

The stationary seat must be

inserted into the seal gland.

The seal assembly is slipped onto the pump shaft

and the set screws tightened in the correct position

The gland is tightened evenly so that the seal

Rotating face and

dynamic O-ring.

Hard Stationary Face

Closing forces exerted

on the seal faces

As the softer carbon face wears down, the rotating face must move to

maintain face closure.

Minute particles of carbon and solids from the process liquid

that migrate across the seal faces build up on the shaft.

METAL BELLOWS

Metal bellows are constructed

series of convolutions is

Now take a look at how a

bellows seal compensates for

face wear.

Metal bellows

Carbon rotating face

Hard stationary face

The bellows core expands to

compensate for face wear.

Debris can build up without causing hang up.

This feature is probably the most notable

selling point when comparing a bellows seal

to a pusher type seal.

Basic multiple seal arrangements A-Unpressurised arrangement

Low pressure buffer fluid between the two seals

High integrity secondary containment

Inboard seal is lubricated by the process fluid

B-Pressurized double arrangement Pressurized barrier fluid between the two seals

Inboard seal is lubricated by the barrier fluid

Note: the mechanical seals can be in four orientations Face-to-back

Back-to-back

Face-to-face

Concentric

Mechanical Seal Arrangement

Unpressurised Arrangements

Fluid is circulated between the seals from an

external supply at a pressure less than the pressure

in the seal chamber. The inboard seal is lubricated

by the process fluid using API Piping Plan 11 (or a

fluid injected into the seal chamber and into the

pump from an external source as a flush using API

Piping Plan32), and the outboard seal is lubricated

by the buffer fluid, forming a high integrity

secondary containment seal. This arrangement

uses API Piping Plan 52


Unpressurized Tandem Seal

Pressurized Arrangements:

Fluid is circulated between the seals from an external supply

at a pressure higher than the pressure in the seal chamber.

Both seals are lubricated by the barrier fluid. This

arrangement uses API Piping Plan 53 (A, B, C or D) or Plan

54.

The pressure between the seals should be maintained at a

minimum of 1 bar or 10% (whichever is higher) above the

maximum process fluid pressure at the inboard seal. This

seal arrangement is not dependent on the process fluid to

lubricate the inboard seal faces because the positive barrier

fluid pressure ensures that the faces are lubricated by the

barrier fluid


Rotating Mechanical Seal

Mechanical seal

Stationary

Mechanical Seal

Impellers

1) Based on major direction of flow

Axial flow

Mixed flow

Radial flow

Impellers

2) Based on mechanical construction

Central hub

Van shroud

Open impeller

Advantage:

It is capable of handling

suspended matter with a

minimum of clogging.

Disadvantage:

Structural weakness if the

vanes are long, they must

be strengthened by ribs or

a partial shroud.

Impellers


Semi-Open impeller

incorporates a single

shroud at the back of the

impeller.

shroud or back wall

Van

Impellers


Enclosed impeller

Advantage:

This design prevents the

liquid recirculation that

occurs between an open or

semi-open impeller as

it incorporates side

walls that totally

enclose the impeller

water ways from the

suction eye

Impellers 3) Based on Suction type

Single suction

Liquid inlet on one side.

Double suction

Liquid inlet to the impeller symmetrically from both sides.

Double Suction Impeller Single Suction Impeller

Shaft

Shaft sleeve

Wear ring

Impeller wear ring

Wear ring

Casing wear ring

Hydraulic loads:

1) Radial thrust:

it is developed when the pump operates at capacities

other than the design one. Thus radial reaction is

created on the impeller.

Hydraulic loads:

1) Radial thrust:

many solutions can be applied to overcome this

radial thrust

a) The double volute casing:

this design depends on

neutralizing radial reaction

forces at reduced

capacities.

Hydraulic loads:

1) Radial thrust:

b) Staggered volutes for multi-stage pump :

this design make the

resultant radial force

is balanced out as

shown.

Hydraulic loads:

2) Axial thrust:

a) in a single stage pump:

in overhung single suction pump the imbalance will

occur when the suction

pressure is either more or

less than the atm.Pressure.

Hydraulic loads:

2) Axial thrust:


in a convential single suction design the

impeller creates

thrust force on itself.

This is due to the

discharge pressure

acting behind the

back and the front

shroud.

Hydraulic loads:

1) Axial thrust:


Solutions:

I. using back radial rips (in

smaller pumps)

Hydraulic loads:

1) Axial thrust:


Solutions:

II. Back wear rings

and balancing

holes

Hydraulic loads:

1) Axial thrust:

b) in a multi stage pump:

balancing the axial thrust is more complex.

the imbalance is caused by:

1. the variance of the pressure distribution on front and

back sides of the impeller

2. the interstage leakage

Hydraulic loads:

1) Axial thrust:


Solutions:

I. back to back arrangement.

II. Conventional arrangement and using hydraulic

balancing device.

Hydraulic loads:

1) Axial thrust:


Solutions:

I. back to back arrangement

Hydraulic loads:

1) Axial thrust:


Solutions:

II. Using hydraulic devices (balancing drum)

Simple balancing disk

Combination balancing disk and drum

Centrifugal Pumps operation

. Operation of centrifugal pumps at reduced flows

There are certain minimum operating flows that must be

imposed on centrifugal pumps for either hydraulic or mechanical reasons.

Four limiting factors must be considered:

- radial thrust,

- temperature rise,

- internal recirculation,

- shape of the brake horsepower curve.

Centrifugal pumps Priming

Single Chamber tank :

a charge of liquid sufficient to prime the pump must be retained in the casing (Fig. A)

When the pump starts, the rotating impeller creates a partial vacuum ; air from the suction piping is drawn into this vacuum and is entrained in the liquid drawn from the priming chamber (Fig. B), then the priming cycle starts.

This cycle is repeated until all of the air from the suction piping has been expelled and replaced by pumpage and the prime has been established (Fig. C).

Fig. A

Fig. B Fig. C

Centrifugal pumps Lubrication

Bearing lubrication

Oil Lubrication methods

Oil bathOil pick-up

ringCirculating

oilOil jet Oil mist Oil-spot

Bearing lubrication

Oil bath

Bearing lubrication

Oil pick-up ring

Bearing lubrication

Circulating Oil

Bearing lubrication

Oil jet

Bearing lubrication

Oil spot

Bearing lubrication

Oil Mist

Oil mist lubrication has not been recommended for some time

due to possible negative environmental effects.

A new generation of oil mist generators permits to produce oil

mist with 5 ppm oil. New designs of special seals also limit

the amount of stray mist to a minimum. In case synthetic

non-toxic oil is used, the environmental effects are even

further reduced. Oil mist lubrication today is used in very

specific applications, like the petroleum industry.

Centrifugal pumps Maintenance

1. Run-to-breakdown maintenance

A machine is repaired after a failure has

occurred. This is a very expensive, since it

requires high cost of spare parts inventory,

long machine downtime, high overtime

labour costs and low production availability.

2. Preventive maintenance

It is performed on a periodic time basis. It is

a planned strategy, which is based on

previous experience and mean-time

between failures. It is not based on the

condition of the machine, but on the time

elapsed since the previous maintenance

occurred. Thus, a failure may occur before

the second maintenance is performed, as in

run-to-breakdown maintenance.

3. Predictive maintenance

It is performed on the basis of the machine condition. This is done using monitoring and recording the machine condition. Any change in

condition is detected and the time to failure is estimated. This is also

accompanied by diagnosing the cause of the fault to actually pin point

the defective components. There are several predictive maintenance

tools. The most effective is by monitoring machinery using vibration

data. This is because many processes generate appreciable vibration

response even if they involve only minute energies. Vibration

measurement in a nondestructive test is performed by reliable off-the-

shelf instrumentation. Thus it can be used under normal operating

conditions to acquire information about inaccessible vibration and the

structural path through which it propagates. It results in lower

maintenance costs. The number of machine breakdowns and faults

are reduced. A successful predictive maintenance program will

incorporate monitoring and diagnositics.

Pumps Bearing arrangement

Anti-friction bearing

mounting methods

Heating Oil InjectionHydraulic

methods

Mechanical

Methods

(cylindrical seating)

Tapered shaft Adapter sleeve Adapter sleeve Withdrawal sleeve

Mechanical Methods

Bearing fitting tool kit

Hook spanners

Impact spanners

Hydraulic Methods

Hydraulic nut

Oil injection

Heating

Oil bath heating method:

Oil used in oil bath heating should have a high flash point and

should not be contaminated

Metallic screen to carry the bearing should not be installed

adjacent to bath bottom surface to avoid direct heating

The bearing should be heated gradually to avoid thermal

stresses

Oil bath heating should not be used with bearing with shields

Bearing with Polyamide cages should not be heated to more

than 85 C

Bearing with metallic cages should not heated to more than

110 C

Induction heaters

Electrical hot plate

Anti-friction bearing

Dismounting methods

Heating Oil injectionHydraulic

Methods

Mechanical

Methods

Mechanical methods

Hydraulic methods(Hydraulic nut)

Oil injection

Heating

Centrifugal pumps Trouble-shooting

Centrifugal pumps alignment

Alignment

When a complete unit is assembled at the factory, the base-plate is placed on a flat, even surface.

The pump and driver are mounted on the base-plate and the coupling halves are accurately aligned, using shims under the driver mounting surfaces where necessary.

Sometimes coupling halves are not true circles or are not of identical diameter because of manufacturing tolerances

pumps course material

Documents

casing casing

split casing

volute casing

circular casing

solid casing

discharge nozzles suction

casing shaft seal

low pressure