CENTRIFUGAL PUMPSGS

PUMP PROVIDES AM MEANS OF ADDING ENERGY TO A FLUID IN ORDER TO HAVE THE CAPABILITY OF TRANSPORTING THE FLUID FROM ONE LEVEL OF POTENTIAL AND KINETIC ENERGY TO ANOTHER.DEPENDING ON A MULTITUDE OF PARAMETERS, VARIOUS MEANS OF ADDING ENERGY ARE EMPLOYED. SOME OF THE MOST PROMINENT CONSIDERATIONS IN MAKING A PUMP SELECTION ARE THE FOLLOWINGS.CAPACITY (FLOW RATE, M3/HR, GPM)DIFFERENTIAL PRESSURE (DIFFERENTIAL HEAD): DISCH.-SUC. PFLUID CHARACTERISTICS: S.G., VISCOSITY, SLURRY, CONTENTS.TEMPERATURESUCTION PRESSURE: KG/CM2, PSIG

PUMPS- Introduction of Pumps

CENTRIFUGALPUMPPUMPS- Various Type of PumpsConventional PumpSealless PumpDiaphragm PumpReciprocating PumpRotary PumpPOSITIVE DISPLACEMENT PUMPVertical PumpMagnetic Driven PumpHorizontal PumpCanned PumpScrew PumpGear Pump

Centrifugal pumps are the most frequently used pumps. They are widely accepted because they combine a relatively low initial cost with high reliability, compact size, non-pulsation flow, and easy maintenance. They are also widely available, cover broad flow / pressure application ranges, and can operate over a wide flow range.

General and Chemical pumps: Non-critical, non-hazardous services. ANSI B73.1 and ANSI B73.2, ISO 2858 pumps

Heavy Duty pumps: Refinery application. Critical, hazardous, heavy duty chemical. API 610.PUMPS- Centrifugal pumps

PUMPS- Various Type of PumpsOH1 : Single stage Overhung Impeller ANSI or ISOEND SUCTIONTOP DISCHARGE

PUMPS- Various Type of PumpsOH2 : Single stage Overhung Impeller API 610

PUMPS- Various Type of PumpsOH3 : Single stage Overhung Impeller, Vertical In-Line Separate Bearing Bracket API 610

PUMPS- Various Type of PumpsOH4 : Single stage Overhung Impeller, Vertical In-Line Rigidly Coupled API 610

PUMPS- Various Type of PumpsOH5 : Single stage Overhung Impeller, Vertical In-Line Closed Coupled (Motor Shaft = Pump Shaft) API 610

PUMPS- Various Type of PumpsOH6 : Single stage Overhung Impeller, Vertical In-Line High Speed Integrally Geared So Called Sundyne Pump API 610

PUMPS- Various Type of PumpsBB1 : Axially Split Between Bearing 1 or 2 Stage Pump API 610

PUMPS- Various Type of PumpsBB2 : Radially Split Between Bearing 1 or 2 Stage Pump API 610

PUMPS- Various Type of PumpsBB3 : Axially Split Between Bearing Multi-Stage Pump API 610

PUMPS- Various Type of PumpsBB4 : Radially Split Between Bearing Multi-Stage Pump So Called Ring Section Pump API 610

PUMPS- Various Type of PumpsBB5 : Radially Split Between Bearing Multi-Stage Pump So Called Double Casing Pump API 610

PUMPS- Various Type of PumpsVS2 (Right)Wet Pit, Vertically Suspended Single Casing Volute with Discharge through the ColumnVS1 (Left)Wet Pit, Vertically Suspended Single Casing Diffuser with Discharge through the ColumnVS3 (Right)Wet Pit, Vertically Suspended Single Casing Axial Flow with Discharge through the Column

PUMPS- Various Type of PumpsVS5 (Right)Vertically Suspended Cantilever Sump PumpVS4 (Left)Vertically Suspended Single Casing Volute Line-Shaft Driven Sump Pump

PUMPS- Various Type of PumpsVS6 (Left)Vertically Suspended Double Casing Diffuser with Discharge through the Column Suitable for Extremely Low NPSHa

PUMPS- Various Type of PumpsConventional Pump VS Magnetic Driven Pump

PUMPS- Basic DesignSuction NozzleDischarge NozzleImpellerMechanical SealRadial BearingThrust BearingShaftBearing HousingSight GlassCasingCenterline Mounted SupportShaft Key

PUMPS- Basic DesignCasingCorrosion allowance shall be Min. 3mm for C.S casing.Min. Nozzle RatingAxially Split 1or 2 stage Pump and Single casing Vertically suspended Pump : 125 # for C.I and 150 # for C.SAll other Pump : 300 #Radial Casing shall be considered if:Pumping Temp 200 Flammable or hazardous liquid with S.G 0.7Flammable or hazardous liquid with Disch. Press. 100 bar G.Centerline Supported in general.

PUMPS- Basic DesignRotorFully enclosed impeller in general.Mechanical seal design conforms to API 682.Renewable Casing Wear Ring and Integral Wear Surface or Renewable Wear Ring for Impeller. H shall be 50 BH unless they have at least 400 BH.Component shall be Dynamically Balanced to ISO G2.5.

PUMPS- Basic DesignBearing

ConditionBearing type and arrangementRadial and thrust bearing speed and life within limits for rolling element bearings and Pump energy density below limitRolling-element radial and thrustRadial bearing speed or life outside limits for rolling-element bearings and Thrust bearing speed and life within limits And Pump energy density below limitHydrodynamic radial and rolling-element thrust or Hydrodynamic radial and thrustRadial bearing speed or life outside limits for rolling-element bearings and Thrust bearing speed and life within limits And Pump energy density above limitHydrodynamic radial and thrustLimits are as follows.a) Rolling-element bearing speed: Factor, n.dm shall not exceed 500 000 where dm is the mean bearing diameter [(d + D)/2)], expressed in millimetres; n is the rotational speed, expressed in revolutions per minute.

b) Rolling-element bearing life: basic rating life, L10, in accordance with ISO 281, equivalent to at least 25 000 h with continuous operation at rated conditions, and at least 16 000 h at maximum radial and axial loads and rated speed.

c) Hydrodynamic radial and thrust bearings shall be used if the energy density [i.e. the product of pump rated power, kW (hp), and rated speed, r/min] is 4,0 106 kW/min (5,4 106 hp/min) or greater.

PUMPS- Basic DesignBearingMost rolling bearings consist of rings with raceways (an inner ring and an outer ring), rolling elements (either balls or rollers) and a rolling element retainer. The retainer separates the rolling elements at regular intervals, holds them in place within the inner and outer raceways, and allows them to rotate freely.

Rolling elements come in two general shapes: ball or rollers. Rollers come in four basic styles: cylindrical, needle, tapered, and spherical.Balls geometrically contact the raceway surfaces of the inner and outer rings at points, while the contact surface of rollers is a line contact.

Theoretically, rolling bearings are so constructed as to allow the rolling elements to rotate orbitally while also rotating on their own axes at the same time.While the rolling elements and the bearing rings take any load applied to the bearings (at the contact point between the rolling elements and raceway surfaces), the retainer takes no direct load. The retainer only serves to hold the rolling elements at equal distances from each other and prevent them from falling out.

PUMPS- Basic DesignBearing - Rolling ElementRolling bearings come in many shapes and varieties, each with its own distinctive features. However, when compared with sliding bearings, rolling bearings all have the followings advantages:

(1) The starting friction coefficient is lower and only a little difference between this and the dynamic friction coefficient is produced.

(2) They are internationally standardized, interchangeable and readily obtainable.

(3) Ease of lubrication and low lubricant consumption.

(4) As a general rule, one bearing can carry both radial and axial loads at the same time.

(5) May be used in either high or low temperature applications.

(6) Bearing rigidity can be improved by preloading.

PUMPS- Basic DesignBearing - Ball versus RollerGenerally speaking, when comparing ball and roller bearings of the same dimensions, ball bearings exhibit a lower frictional resistance and lower face run-out in rotation than roller bearings.

This makes them more suitable for use in applications which require high speed, high precision, low torque and low vibration.

Conversely, roller bearings have a larger load carrying capacity which makes them more suitable for applications requiring long life and endurance for heavy loads and shock loads.

PUMPS- Basic DesignBearing - Radial and ThrustAlmost all types of rolling bearings can carry both radial and axial loads at the same time.

Generally, bearings with a contact angle of less than 45 have a much greater radial load capacity and are classed as radial bearings; whereas bearings which have a contact angle over 45 have a greater axial load capacity and are classed asthrust bearings.

There are also bearings classed as complex bearings which combine the loading characteristics of both radial and thrust bearings.

PUMPS- Basic DesignBearing - Rolling ElementDeep groove ball bearingAngular contact ball bearing

PUMPS- Basic DesignBearing - Rolling ElementCylindrical roller bearingNeedle roller bearing

PUMPS- Basic DesignBearing - Rolling ElementTapered roller bearingSpherical roller bearing

PUMPS- Basic DesignBearing - Rolling ElementThrust ball bearingThrust roller bearing

PUMPS- Basic DesignLubricationUnless otherwise specified, bearings and bearing housings shall be designed for oil lubrication using a mineral (hydrocarbon) oil.Pressurized Lube oil system may be required if High Energy shall be supported by the bearing.1 rotating equipment2 filter3 electric motor4 pump5 internal baffle6 max. operating level7 min. operating level8 pump suction level9 heater (optional)10 sloped bottom11 drain12 shaft-driven oil pump with integral pressure relief13 TCV (optional)14 cooler

PUMPS- Basic DesignDriver It can be electrical motor and/or general purpose steam turbine.For electrical motor, following information shall be issued by the purchaser.Area classificationVoltage / Phase / HertzAmbient temp / ElevationExplosion Proof Grade, Weather Proof GradeDriver shall have the margin as defined in API 610 as minimum. It shall be sized to accommodate all specified process variation such as changes in capacity, differential pressure, S.G and viscosity.

Motor nameplate ratingPercentage of rated pump power (%)kWHP< 22< 3012522 to 5530 to 75115> 55> 75110

PUMPS- Basic DesignCouplingMetal flexible element, spacer-type couplings in accordance with AGMA 9000 Class 9 shall be provided. Flexible elements shall be of corrosion-resistant material.Couplings shall be designed to retain the spacer if a flexible element ruptures.Coupling hubs shall be steel.The spacer nominal length shall be at least 125 mm (5 in) and shall permit removal of the coupling, bearings, seal and rotor, as applicable, without disturbing the driver or the suction and discharge piping.If specified, couplings shall be balanced to ISO 1940-1 grade G6.3.

PUMPS- Basic DesignMaterials Pump Parts

Service

Temp ()

Material Class

Casing

Impeller

Shaft

Wear Ring

Boiler Feed Water

> 95

C-6

Axially Split

12% Cr

12% Cr

12% Cr

12% Cr Hd

S-6

Barrel

Carbon Steel

12% Cr

AISI 4140

12%Cr (N1)

12% Cr Hd

Sea Water

< 95

(N2)

Ni Resist D2

316 S.S

Alloy 400

Sour Water

< 260

D-1

S-6 (N3)

Duplex S.S

Duplex S.S

Duplex S.S

Duplex S.S Hd

Hydrocarbon

< 230

S-1

S-4 (N4)

Carbon Steel

Cast Iron

Carbon Steel

Cast Iron

230~370

S-6

S-4 (N5)

Carbon Steel

12% Cr

AISI 4140)

12% Cr Hd

> 370

C-6

12% Cr

12% Cr

12% Cr

12% Cr Hd

Amine

< 150

S-8

Carbon Steel

316 S.S

316 S.S

316 S.S Hd

N1) When Pumping Temp > 175

N2) For Sea Water Service, Vendor and Purchaser shall agree on the Materials. It shows only

examples for vertical type Cooling Water Pumps.

N3) When H2S rate is not severe, S-6 can be applied. Such decision shall be made by Process.

N4) S-1 Class is getting less popular by the need of material uniformity for spare parts. S-4 now days generally

accepted for the minimum requirement for hydrocarbon service.

N5) When the corrosivity of pumping liquid is low, S-4 can be used.

PUMPS- Performance EvaluationPressure ATM (Atmospheric Pressure): , Gauge Pressure: + Vacuum Pressure Absolute Pressure: .

Head: m = {10 x Pressure (kg/cm2)} / S.G

Specific Gravity (S.G.): , 4

Power (kw) kw = {(kgf/m3) x Total head (m) x flowrate (m3/h) } / 102 BHP: pump motor pump

-Efficiency

PUMPS- Performance Evaluation

PUMPS- Performance EvaluationHEAD INCREASEPumps shall be capable of at least a 5 % head increase at rated conditions by replacement of the impeller(s) with one(s) of larger diameter or different hydraulic design, variable-speed capability or use of a blank stage.QHMin. ImpellerMax. ImpellerRated ImpellerRated CapacityRated HeadHead @ Max. Impeller Head @ Max. ImpellerHead Increase = ------------------------------ Rated Head

PUMPS- Performance EvaluationHEAD RISEPumps that have the continuous head rise to shutoff are preferred for all applications and are required if parallel operation is specified. If parallel operation is specified, the head rise from rated point to shutoff shall be at least 10 %. If a discharge orifice is used as a means of providing a continuous rise to shutoff, this use shall be stated in the proposal.QHMin. ImpellerMax. ImpellerRated ImpellerRated CapacityRated HeadShutoff Head Shutoff HeadHead Rise = ------------------ Rated Head

PUMPS- Performance EvaluationNPSH MarginNPSHa = Net Positive Suction Head AvailableThis is the pure suction head (or pressure) that system can give to the pump after extracting all and any losses. It shall be calculated by the system designer.

NPSHa = Suct. Press.+Liquid Elevation (Liquid Vapor Press.+All Losses)To match the unit to Head (length), Press. To be divided by Density

NPSHr = Net Positive Suction Head RequiredThis is the pure suction head (or pressure) that pump needs from the system. It is peculiar of each model of pump, hence, it shall be proposed by pump vendor.NPSH margin = NPSHa - NPSHr specified requirement

PUMPS- Performance EvaluationSPECIFIC SPEEDThe best way to describe the shape of an impeller is to use its specific speed number. Specific speed is calculated for the pumps performance at best efficiency point with the maximum diameter impeller. This is a dimensionless number that was generated by the formula :

PUMPS- Performance EvaluationSUCTION SPECIFIC SPEED

Suction-specific speed is calculated for the pumps performance at best efficiency point with the maximum diameter impeller and provides an assessment of a pumps susceptibility to internal recirculation. It is expressed mathematically by the following equation:

PUMPS- Performance EvaluationMINIMUM FLOW

Minimum Continuous Stable Flow (MCF) Shaft, Bearing pump vibration, noise ( BEP 10% )

Minimum Thermal Flow (MTF)

PUMPS- Performance EvaluationCAVIATIONThe pressure of the liquid in a centrifugal pump drops as it flows from the suction flange through the suction nozzle and into the impeller. The amount of pressure drop is a function of many factors, including pump geometry, rotational speed, frictional and hydraulic shock losses, and flowrate. If the pressure at any point within the pump falls below the vapor pressure of the liquid being pumped, vaporization or cavitation will occur.

HOW TO DETERMINE NPSHrThe pump manufacturer determines the NPSHr of an impeller pattern by conducting a suppression test using water as the pumped fluid. These tests are usually only made on the first casting for an impeller pattern, not on individual pumps.

Normally, the NPSHr plotted on the traditional pump curve is based on a 3% head loss due to cavitation, a convention established many years ago in the Hydraulic Institute Standards. Permitting this large a head loss means that cavitation would already have been occurring, at some higher flow condition, before performance loss was noticed.

PUMPS- Performance EvaluationCLASSIC CAVIATIONClassical cavitation occurs when the absolute pressure of a moving liquid is reduced to, or even below, the vapor pressure of the liquid in the impeller eye. Bubbles are formed as a result of this pressure drop. Lower pressures in the impeller eye are caused by variations in velocity of the fluid and friction losses as the fluid enters the impeller.The bubbles are caught up and swept outward along the impeller vane. Somewhere along the non-visible side of the impeller vane, the pressure may once again exceed the vapor pressure and cause the bubbles to collapse.Implosions of these vapor pockets can be so rapid that a rumbling/cracking noise is produced (it sounds like rocks passing through the pump). The hydraulic impacts caused by the collapsing bubbles are strong enough to cause minute areas of fatigue on the metal impeller surfaces. Depending on the severity of the cavitation, a decrease in pump performance may also be noted.The first reaction to a cavitation problem is usually to check the NPSHa at the eye of the impeller and compare this to the NPSHr by the impeller design. The ratio of NPSHa/NPSHr must be sufficiently large to prevent the formation of cavitation bubbles.Keep in mind that very few process applications call for a pump to handle a pure liquid such as water. Most services handle a mixture of various components (e.g., crude oil, blended gasoline or even paint). As such, they will have a range of vapor pressures or boiling points, which depend on the volatility of each component.Cavitation damage to a centrifugal pump may range from minor pitting to catastrophic failure and depends on the pumped fluid characteristics, energy levels and duration of cavitation.

PUMPS- Performance EvaluationINTERNAL RECIRCULATION CAVIATION (1)Recirculation cavitation is a term used to describe the formation of vapor-filled pockets. This type of cavitation is less well known and understood than classical cavitation.

As the pump is operated back on its curve, eddy currents begin to form in the eye of the impeller. There is no reduction in mass flow through the pump at a given point on this curve. This means that the velocity through the impeller fluid channels must have increased. That is, the eddy currents at the eye have effectively reduced the flow channel size, thereby increasing liquid velocity for the fixed flowrate.

When the velocity increases, the pressure drop due to friction must also increase.

If the drop is large enough to cause the pressure to fall below the liquid's vapor pressure, the pump will develop classical cavitation because of the initiating action of recirculation cavitation.

PUMPS- Performance EvaluationINTERNAL RECIRCULATION CAVIATION (2)Another cause of recirculation is that as the fluid flows over an impeller vane, the pressure near the surface is lowered, and the flow tends to separate.

This separated region occurs when the incidence angle--the difference between flow angle and pump impeller vane inlet angle--increases above a specific critical value.

The stalled area eventually washes out but is reformed as rotation continues. The area contains a vapor surrounded by a turbulent flowing liquid at a higher pressure than the vapor pressure.

This separated region will then fill with liquid from the downstream end. The vapor pocket collapses, which causes damage to the surface of the impeller vane. This may occur up to 200 to 300 times per sec.

PUMPS- Performance EvaluationHOW TO IDENTIFY CLASSIC CAVIATION AND INTERNAL RECIRCULATION CAVITATION1. Classical cavitation. Damage is located on the non-visible or underside of the vane. It starts near the leading edge and can extend up to approximately two-thirds of the vane length before the pressure implodes the bubbles. Either feeling or looking at the underside of the vane with a mirror is necessary to evaluate the damage.

2. Suction recirculation.Damage is on the visible or the pressure side of the vane's leading edge. If tip recirculation has occurred, damage will be on the visible or pressure side of the vane near shroud walls.Note that this damage will be on the opposite side of the vane as that which occurred with classical cavitation. This continuous recycling results in noise, vibration and pressure pulsations. These results imitate classical cavitation, and thus recirculation is often incorrectly diagnosed as such.