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ChE 203
More on Pumps
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Contents
Basic Conversions Series and Parallel Configurations
Reciprocating Pumps
Rotary Pumps Rotary Lobe Pumps
Pump Performance
Centrifugal v/s PD pumps
Liquid Ring Vacuum Pumps
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Converting Head to Pressure
Convert ing head in m eter to pressure in bar
p = 0.0981 h (1)where
h = head (m)
p = pressure (bar)
Convert ing head in meter to pressu re in kg /cm2
p = 0.1 h (2)where
h = head (m)
p = pressure (kg/cm2)
Convert ing head in feet to pressure in ps i
p = 0.434 h (3) where
p = pressure (psi)
h = head (ft)
= specific gravity
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Converting Pressure to Head
Since pressure gauges often are calibrated in pressure - psi or bar, it
may be necessary with a conversion to head - feet or meter, commonused in pump curves.
Convert ing pressure in kg/cm2to head in meter
h = p 10 / (4)
where h = head (m)
p = pressure (kg/cm2
)
Convert ing pressure in bar to head in meter
h = p 10.197 / (5)
where h = head (m)
p = pressure (bar) Convert ing pressure in psi to h ead in feet
h = p 2.31 / (6)
where h = head (ft)
p = pressure (psi)
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Pumps in Serial - Heads Added
When pumps are arranged in series, their resulting pump
performance curve is obtained by adding heads at the same
flow rate.
For two identical pumps the head will be twice the head of a
single pump at the same flow rate.
Two Pumps in Series
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Pumps in Parallel - Flow Rate Added
When pumps are arranged in parallel, their resulting
performance curve is obtained by adding their flow rates at the
same head.
For two identical pumps the flow rate will be twice the flow
rate of a single pump at the same head
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Pump Types
Pumps
Positive Displacement Centrifugal
Reciprocating Rotary
Plunger/Piston
Diaphragm
Lobe/Gear
Vane
Gear
Screw
Radial Axial Mixed Flow
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Reciprocating Pump Types
Single Acting piston pump
discharge curve
Simplex Double Acting piston
pump discharge curve
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Reciprocating Pumps Flow
Characteristics
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Pulsation Dampeners
A pulsation damper absorbs only that portion of piston displacement
above mean flow, and then stores it momentarily before discharging it
during the portion of the cycle below mean flow (on the suction stroke).
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Why?
Reduce high pressure fluctuations in the piping system that caneither overpressure or fatigue components in the piping system
Attenuate the frequency of the pressure pulsations produced by thepump
Eliminate relief-valve chatter
Provide relatively steady flow if large variations cannot be tolerated
by the process Reduce acceleration head and friction losses to maximize NPSHAwhen installed as a suction stabilizer in the suction piping
Reduce pump brake horsepower
Minimize check valve wear
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Dampener Working Principle
Half way through the pistons forward travel (discharge stroke), fluid
velocity between the discharge check valve and the pulsationdamper begins to decay.
The corresponding drop in pressure causes the membrane inside thedamper to expand, since the internal gas pre-charge pressure is nowhigher than the line pressure.
The (stored) fluid now being displaced by the pulsation damper
maintains velocity downstream of the damper thereby reducing, if noteliminating, any downstream pulsations.
A pulsation damper removes pulses only from the line downstream ofthe dampernot upstream.
Discharge damper installations to be made as close to pumpdischarge nozzles as possible.
In an application of a damper for suction stabilization (reduction ofacceleration head losses) it is the velocity gradient between thesupply vessel and the suction nozzle that is minimized.
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Bladder Type Pulsation Dampener
Single liquid connection at one
end of the metal housing A gas-charging valve at the other
end with the bladder between.
The gas volume acts as a spring,compressing and expanding tomeet liquid system pressure
changes. Shown: charging valve, bladder in
the middle of the bottle, the anti-extrusion button, the port,Gas/liquid phases.
The charging must be made with atmospheric pressure at the liquid
port.
The pre-charge should be set between 50 percent and 70 percent of the
system pressure.
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Diaphragm Pumps
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Wilden T2 - 25 mm (1") Metal Pump FLOW RATE
Rubber/TPE 133 lpm(35 gpm) Teflon 95 lpm(25 gpm)
MAX PRESSURE 8.6 bar (125 psig)
MAX. SOLIDS PASSAGE
3.2 mm (1/8")
MAX. SUCTION LIFT (wet): Rubber/TPE 9.5 m (31.0')
Teflon 9.5 m (31.0')
(dry): Rubber/TPE 5.2 m (17.0')
Teflon 1.8 m (6.0')
SPECIFICATIONS Height: 279 mm (11.0")
Width: 268 mm (10.5")
Depth: 184 mm (7.3")
Air Inlet: 6 mm (1/4" FNPT)
Liquid Inlet: 25 mm (1")
Liquid Outlet: 19 mm (3/4")
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Flow Curve
To pump 394 lpm against a discharge pressure head of 1.4 bar requires 4.1 bar and 102
Nm3/hr air consumption. Dot on chart represents the plotted intersection and the circled
numbers are the air pressure and volume figures.
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Installation
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Discharge regulation
Limiting the volume and/or pressure of the air supply to the pump.
An air regulator is used to regulate air pressure. A needle valve isused to regulate volume.
Throttling the pump discharge by partially closing a valve in thedischarge line of the pump. This action increases friction loss whichreduces flow rate (control the pump from a remote location).
When the pump discharge pressure equals or exceeds the air supply
pressure, the pump will stop; no bypass or pressure relief valve isneeded, and pump damage will not occur.
The pump has reached a deadhead situation and can be restartedby reducing the fluid discharge pressure or increasing the air inletpressure.
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Surge Dampening
As the reciprocating pump begins its stroke, the liquid discharge pressureincreases and flexes the diaphragm inward, accumulating fluid in theliquid chamber.
When the pump redirects its motion, the liquid discharge pressuredecreases allowing the diaphragm to flex outward displacing the fluid intothe discharge line
A compressed air line attached to the air side of the air regulator bodysets and maintains pressure on the air side of the diaphragm.
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Efficiency of Reciprocating Pump
There are only two efficiency losses Volumetric and Mechanical.
Volumetric efficiency loss is induced by slippage through valves,
ratio of liquid chamber volume at end of stroke to plunger/piston
displacement volume, and liquid compressibility.
Mechanical efficiency loss occurs while overcoming mechanical
friction in bearing and speed reduction.
The overall efficiency of a reciprocating pump unit is generally above85 percent throughout its full operating range.
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Rotary Pumps
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Internal Gear Pumps Advantages Two moving parts
One stuffing box Positive suction, non-pulsating discharge
Ideal for high viscosity liquids
Constant and even discharge regardless of varying
pressure conditions
Low NPSH required
Easy to maintain
Disadvantages
Low speeds usually required
Medium pressure One bearing runs in pumped product
Overhung load on shaft bearing
Internal gear pumps are ideal for hig h-v iscos ity l iquid s, bu t they
are damaged w hen pump ing large sol ids .
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External Gear Pumps
Advantages
High speed
Medium pressure
No overhung bearing loads
Relatively quiet
Design lens itself to use of a wide variety of materials Disadvantages
Four bushings in liquid area
Four stuffing boxes
No solids allowed
External gear pum ps (shown is a
double pump) are typical ly used for
h igh -pressure appl icat ions such as
hydraul ics
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Lobe Pumps
Advantages
Pass medium solids
High acceptance
Little galling (frictional wear) possibility
Disadvantages
Timing gears More space required
May require factory service to repair
Two seals
Lobes in lobe pum ps do not m ake contact ,
because they are dr iven b y external tim ing g ears
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Sliding Vane Pumps
Advantages
Medium capacity Medium speed
Thin liquids
Sometimes preferred for solvents, LPG
Can run dry for short periods
Can have one seal or stuffing box Develops good vacuum
Disadvantages
Can have two stuffing boxes
Medium pressure
Complex housing
Not suitable for high viscosity
Not good with abrasives
Vane pumps have better dry pr iming
capabi l i ty than other pos it ive
displacement pumps.
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Rotary Pump Applications
Pump Selection Guide
Abrasives Thin Liquids Viscous Solids Dry PrimeDiff.
Pressure
Internal Gear G G E P A G
External Gear P G G P A E
Lobe G A E E A G
Vane P E A P G A
E = Excellent, G = Good, A = Average, P = Poor
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Rotary Lobe Pumps
Attributes include:
Gentle transfer of delicate
suspended solids.
Bi-directional operation.
Compact size with high
performance and lowenergy input.
Ability to pump shear
sensitive media.
Easy maintenance.
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EOU Dryer Feed Pump
FEED PUMPS 61P1, 62 P1, 63 P1
Make SRU2/018/HS withAINSI B16.5 Flange
Impeller Dia Trilobe
Motor Make Siemens
Motor rating 1.5kW/2 HP
Motor rpm 1420 rpm
Rated rpm 200 RPM
Fluid Sp Gr 1.3
Fluid temperature 30 C
Shanti Gear Box Type F20-YU and 2 HPND 90L
Coupling Guard SS 304
Plain Base Frame SS 304
H= Vertical
orientation
S= SS shaft
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Pump System Design
Confirm the Net Positive Suction Headrequirements of the pump (NPSHr) are met by thesystem, as this is crucial for ensuring the smoothoperation of the pump and preventing cavitation.
Avoid suction lifts and manifold/common suction
lines for two pumps running in parallel, as this maycause vibration or cavitation.
Protect the pump against blockage from hard solidobjects e.g. nuts, bolts etc.
Also protect the pump from accidental operation
against a closed valve by using one of the followingmethods: - relief valves, pressure switch, andcurrent limiting device.
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Slip
Slip is the fluid lost by leakage through the pump clearances.
The direction of slip will be from the high pressure to the low
pressure side of the pump i.e. from pump outlet to pump inlet.
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Factors Affecting Slip
The amount of slip is dependent upon
Pressure
Clearance
Viscosity.
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Pump Characteristic and System Curve
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Pump Performance Curve
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Net Positive Inlet Pressure (NPIP)
NPIPA = Pa +/- Pz - Pf - PvpPha
where NPIPA = net positive suction head available, kPa
Pa = absolute pressure working on the fluid in the suctionvessel or sump, kPa
Pvp = vapor pressure of the fluid being pumped at the
pumping temperature, kPa Pz = static height above (+) or below (-) centerline of the
cylinder, kPa
Pf = piping friction loss, m(based on equivalent length) kPa
Pha = acceleration head, m (based on actual length) kPa
NPIP Required (NPIPR) is a function of pump type, speed andviscosity of fluid pumped.
NPIPA must always be greater than NPIPR to preventcavitation.
NPIPR values published by manufacturers are expressed in
kPa units.
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NPIP- Rotary Pumps
Rotary pumps are often selected to move liquids with a low vapor
pressure point, or fluids with a lot of entrained bubbles. NPIP required (NPSH) is difficult to test and is established at the
point where
Cavitation noise is heard.
A 5% reduction in capacity at constant differential pressure and
speed A 5% reduction in power consumption at constant differential
pressure and speed.
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Flow Regulation
Discharge throttling
Not Possible Suction throttling
Not possible Recycle control
Efficient method of control for PD pumps. The flow rate constant, the power requirement is roughly
proportional to discharge pressure. The effect of recycle is to drop the discharge pressure, it results
in reductions in power requirement. Power wasted is in proportion to discharge pressure times
recycle flow. Speed Control Stroke Adjustment
C t if l V P iti
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Centrifugal Versus Positive
Displacement Effect of Viscosity
C i
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ComparisonParameter Centrifugal Pumps Reciprocating Pumps Rotary Pumps
Optimum Flowand PressureApplications
Medium/High Capacity,Low/Medium Pressure
Low Capacity,High Pressure
Low/Medium Capacity,Low/Medium Pressure
Maximum FlowRate
20000+ m3/h 2000+ m3/h 2000+ m3/h
Low Flow RateCapability
No Yes Yes
MaximumPressure
400+ kg/cm2 7000+ kg/cm2 250+ kg/cm2
Requires ReliefValve
No Yes Yes
Smooth orPulsating Flow
Smooth Pulsating Smooth
Variable orConstant Flow
Variable Constant Constant
Self-priming No Yes Yes
SpaceConsiderations
Requires Less Space Requires More Space Requires Less Space
Costs Lower Initial
Lower MaintenanceHigher Power
Higher Initial
Higher MaintenanceLower Power
Lower Initial
Lower MaintenanceLower Power
Fluid Handling Suitable for a wide rangeincluding clean, clear, non-abrasive fluids to fluids withabrasive, high-solid content.Not suitable for highviscosity fluidsLower tolerance forentrained gases
Suitable for clean, clear, non-abrasive fluids. Specially-fittedpumps suitable for abrasive-slurry service.Suitable for high viscosityfluidsHigher tolerance for entrainedgases
Requires clean, clear, non-abrasive fluid due to closetolerances
Optimum performance with highviscosity fluidsHigher tolerance for entrainedgases
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Liquid Ring Vacuum pumps
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Operating Principle
An impeller (A) is mounted eccentric toa round pump body (B) and enclosedbetween two endplates.
As the body is partially filled withservice liquid before operation, theimpeller rotation creates a liquid ring(C) concentric to the body by the actionof centrifugal force.
As the cavities pass the suction port,
the volume of liquid within themreduces, and this in-turn creates anegative pressure. This acts as thepumps suction, drawing more gas fromthe vessel to be evacuated.
As the impeller continues to rotate,these cavities become filled with theliquid ring, and the entrained gas is
compressed. As rotation continues past thedischarge port, all gas and someservice liquid is forced out of the pump.
The liquid ring can be regeneratedthrough the use of a separator (D).
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Design Data
Inlet pressure, usually expressed in mm Hga
Inlet temperature Mass flow rate, usually expressed in kg/hr and the molecular weight
of fluid components
Vapor pressure data for each fluid component
Seal fluid data, if other than water: specific gravity, specific
Heat, viscosity, thermal conductivity, molecular weight and vaporpressure data
Temperature of the seal fluid or cooling water
Discharge pressure, usually expressed in kg/cm2
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How To Avoid Cavitation
Use a colder seal fluid.
Use a seal fluid with a lower vapor pressure. The seal fluid shouldbe compatible with the process gas mixture and the materials ofconstruction.
Increase the inlet operating pressure beyond the range ofcavitation.
Check the loading and operating pressure. If the load is less than
design, a vacuum relief valve or air bleed valve can be used tointroduce additional load so the pump will be able to operate closerto the design pressure.
Install a booster upstream of the liquid ring vacuum pump tocompress and raise the absolute pressure of the vacuum pumpsuction.
An ejector works by using pressure energy of the motive toincrease the velocity of the entrained gas load. This produces ahigher absolute pressure at the outlet of the ejector.
Increase the throughput of seal fluid, if possible.
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