Pumps Selection and Sizing and Troubleshooting
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Transcript of Pumps Selection and Sizing and Troubleshooting
Department of Polymer and Process Engineering,
University of Engineering and Technology, Lahore
Fluid Flow (Lab)Subject Code: PolyE- 203
Topic:Selection of Pumps
and their Sizing,Their Materials of
Cinstruction and Troubleshooting
Group PresentationGroup#6
Grooup Leader:
Mujadid ul Hassan Khawaja
2010-PE-51 Department of
Polymer and Process Engineering, UET Lahore
Members
Syed Mohsin Ali Rizvi
2010-PE-57 Department of
Polymer and Process Engineering, UET Lahore
Members
Hafiz Adnan Mehmood
2010-PE-28 Department of
Polymer and Process Engineering, UET Lahore
Table of Contents:
1. Introduction to Pumps2. Major Classification of pumps and their
Working3. Materials of Construction of Pumps4. Some important terminologies related
to Pumps5. Selection of Pumps6. Sizing, Metering and proportionating
of pumps7. Troubleshooting of pumps
1.Introduction to Pumps And their Classification
Presenter:Mamoon Shahid
What are pumps
Pumps are device used to move fluids. They move fluids by using mechanical action.
Component of pumping system
The main components of a pumping system are:
Prime movers: electric motors , diesel engines or air system.
Piping, used to carry the fluid.
Valves, used to control the flow in the system.
Classification of pumps
Pumps
Dynamic Positive
displacement pump
Axial Flow Pumps
1. Single Stage Pump
Axial Flow Pumps
Opened, Closed and Semi Closed Impellers
Centrifugal Pumps on the Basis of Suction Postition
Dynamic pumps
Energy is added to fluid velocity
At discharge end velocity is reduced and pressure is increased
There are two types of dynamic pump1.Centrifugal pump2.Special effect pumps
Centrifugal pump
Its purpose is to convert energy of a prime mover first into velocity or kinetic energy and then into pressure energy of a fluid that is being pumped.
A centrifugal pump can be single stage or multi stage.
Working mechanism
Working mechanism can be expressed in two steps
1) Generation of centrifugal forces
2) Conversion of kinetic energy to pressure energy
Generation of centrifugal forces
The process liquid enters the suction nozzle and then into eye (center) of a revolving device known as an impeller.
When the impeller rotates, it spins the liquid.
Because the impeller blades are curved, the fluid is pushed in a tangential and radial direction by the centrifugal force.
Conversion of kinetic energy to pressure energy
The key idea is that the energy created by the centrifugal force is kinetic energy.
The faster the impeller revolves or the bigger the impeller is, then the higher will be the velocity of the liquid at the vane tip and the greater the energy imparted to the liquid.
Conversion of kinetic energy to pressure energy
This kinetic energy of a liquid coming out of an impeller is harnessed by creating a resistance to the flow. The first resistance is created by the pump volute (casing) that catches the liquid and slows it down.
In the discharge nozzle, the liquid further decelerates and its velocity is converted to pressure according to Bernoulli’s principle.
Working mechanism
Energy changes
Impeller Diffuser
Components of a centrifugal pump
The main components of a centrifugal pump are
1. Rotating components: an impeller coupled to a shaft.
2. Stationary components: casing, casing cover, and bearings.
Impeller
An impeller is a circular metallic disc with a built-in passage for the flow of fluid.
Impellers are generally made of bronze, polycarbonate, cast iron or stainless steel, but other materials are also used.
Shaft
• The shaft transfers the torque from the motor to the Impeller during the startup and operation of the pump.
Shaft
Casing
The main function of casing is to enclose the impeller at suction and delivery ends.
A second function of casing is to provide a supporting and bearing medium for the shaft and impeller.
Volute casing
A volute is a curved funnel increasing in area to the discharge port .
Circular casing
Circular casing has stationary diffusion vanes surrounding the impeller periphery that convert speed into pressure energy.
2.Postive Displacement
Pumps,Their Major Types and
working
Presenter:Hafiz Adnan Mehmood
Positive Displacement Pumps
Contents Introduction
Construction & working
Types
Introduction
A positive displacement pump is one in which a definite volume of liquid is delivered for each cycle of pump operation. This principle applies to all types of positive displacement pumps
Construction & working
Positive Displacement Pumps has an expanding cavity on the suction side and a decreasing cavity on the discharge side.
Liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses.
Working and Construction
A Positive Displacement Pump must not be operated against a closed valve on the discharge side of the pump because it has no shut-off head like Centrifugal Pumps.
A Positive Displacement Pump operating against a closed discharge valve, will continue to produce flow until the pressure in the discharge line are increased until the line bursts or the pump is severely damaged - or both.
Working and Construction Positive Displacement Pumps are "constant
flow machines“.
A relief or safety valve on the discharge side of the Positive Displacement Pump is therefore absolute necessary.
The relief valve can be internal or external.
Types
There are two main types of PD pumps
Reciprocating pumps
Rotary pumps
Reciprocating pumps
Reciprocating pumps are those which cause the fluid to move using one or more oscillating pistons, plungers or membranes (diaphragms).
Plunger pumps
Diaphragm pumps
Diaphragm pump
Plunger pump
Working of Plunger pump Plunger pumps comprise of a cylinder
with a reciprocating plunger in it.
In the head of the cylinder the suction and discharge valves are mounted. In the suction stroke the plunger retracts and the suction valves opens causing suction of fluid into the cylinder.
In the forward stroke the plunger push the liquid out the discharge valve.
Rotary Pumps
Displacement by rotary action of gear, cam or vanes
Typical rotary pumps are
Gear pumpsLobe pumpsVane pumpsCam pumpsScrew pumps
Gear pumps
Cont. . .
In gear pumps the liquid is trapped by the opening between the gear teeth of two identical gears and the chasing of the pump on the suction side.
On the pressure side the fluid is squeezed out when the teeth of the two gears are rotated against each other.
the gear pump is well suited for handling viscous fluids such as fuel and lubricating oils.
Rotary pumps are further classified such as internal gear, external gear, lobe and slide vane etc
Lobe pumps
Effects of Pressure & Viscosities on PD Pumps
PressureChange in Pressure have little effect on the
PD pump efficiency.
ViscosityWhen the viscosity of fluid increases the
flow also increase in PD pumps. The reason is the liquid fill in the clearances of the pump causing a higher volumetric efficiency .
•if there is changing viscosity in the application the PD pumpis the best choice.
Presenter:Mohsin Ali Rizvi
4. Materials of
Constructions of Pumps
Material of construction
The pumps have different parts ; Impeller , casing , shaft and wear rings etc When selecting the material for the impeller, the following several criteria
should be considered
Corrosion resistance
Abrasive wear
resistance
Cavitations resistance
Casting & machining properties
Material of construction
Bronze Impellers used for many water and noncorrosive services but these impellers should
not be used for pumping temperature in excess of 120°C Types:
1. Leaded bronze2. Non leaded bronze3. Nickel aluminum bronze
Leaded bronze Impellers Used extensively in past because the lead addition to bronze enhances its
cast ability and machine ability but due to environmental problems they have been replaced by Non-leaded bronze impellers.
Bronze Impellers
Material Of Construction
Non-Leaded Bronze Impellers Although they are efficient than leaded bronze impellers but they have velocity
limitations above which they cannot be used because they will suffer accelerated erosion corrosion. So they are used where not so high speed is required.
Nickel Aluminum Bronze Impellers These impellers are used specially in salt water applications because of their high
mechanical properties, good corrosion resistance and the capability to be weld repaired. They are also designed for higher speed than any other bronze alloy impellers.
Cast iron Impellers They are used to a limited extent in small ,low cost pumps. This material is inferior
than bronze in corrosion and cavitation resistance also it can not be welded to repair damage. So only the low cost is the mere justification for the cast iron impeller usage.
Material Of Construction
Martensitic Stainless Steel Impellers They are used in the place of bronze impellers where bronze does not satisfy the
requirements for cavitation resistance, corrosion and erosion. These impellers are used in boiler feed water, many cooling waters and a variety of cooling applications They do not have pitting corrosion for use in sea water.
Martensitic Stainless Steel Impellers These impellers are used where higher level of corrosion resistance is required.
1. Austenitic grades having 6% molybdenum for use in salt water2. Austenitic grades having 20% nickel for the sulphuric acid applications3. Chrome manganese alloy to eliminate cavitation resistance
Material Of Construction
Duplex Stainless Steel These impellers are used because of their higher mechanical properties, better corrosion
resistance and weld ability. Nitrogen addition in it improves its cast ability and weld ability. These impellers are widely used in mining ,flue gas desulfurization, paper and pulp industry and for the marine applications. Specially they are used in high pressure water injection in the oil industry.
It should contain 25% chromium, 3%molybdenum and 0.15% nitrogen.
Material of construction
When selecting the material for the Casing of pump, the following several criteria should be considered
Corrosion resistance
Abrasive wear
resistance
Cost and strength
Casting & machining properties
Weld ability (for repair)&
cost
Material Of Construction
Cast iron Casing
For single stage pumps , cast iron casing is used because it has sufficient for pressure developed. (discharge pressure up to 1000lb/sq.inch and temperature up to 177 C).
For multi-stage pumps and pressure up to 2000lb/sq.inch a cast steel is used and for the pressure above this forged steel barrel type casing is used.
Ductile iron casing can be used instead of cast iron as its tensile strength is double as compared to cast iron. They can used as a substitute for steels in the intermediate temperature range. But they can not be effectively repaired or welded
Material Of Construction
Austenitic Irons Casing They are commonly known by their trade name Ni-resist, are used where ductile irons have
insufficient corrosion resistance. They typically contain 15-20% Ni and are used in brackish and salt water applications. But they poor towards welding that’s why its new modified grade D2W is used which
contains columbium that enhances its weld ability.
Bronze Casing Leaded bronze, Non-leaded bronze, Tin bronze, Ni-Al bronze are alloys used for the casing
depending upon the application. Among them Ni-Al type is expensive and are usually not competitive on cost basis with Ni-resist or other alternatives
Material Of Construction
Steel Casings
1. Stainless Steel2. Martensitic stainless Steel3. Austenitic Stainless Steel4. Duplex Stainless Steel All these materials have their own usage according to applications. The first one is used
for better corrosion resistance, second one is used for high pressure applications and in many hydrocarbons applications, the third one in chemical applications and corrosive services and Duplex is used where corrosion resistance and mechanical properties higher than other austenitic grades are required
Material of construction
When selecting the material for the shaft, the following several criteria should be considered
Corrosion resistance
wear resistance
Cost and strength
Endurance limit
Notch sensitivity
Material Of Construction
The several materials for shaft are available according to the specifications.
1. Carbon steel 2. Stainless steel 3. Martensitic stainless steel etc These materials should have low cost and high wear resistance and good endurance limit that’s
why a shaft can be plated or coated for an improved corrosion resistance and wear. Chrome plating is one of the example.
Material of construction
When selecting the material for the Wear rings, the following several criteria should be considered
Corrosion resistance
Abrasive wear
resistance
Casting and machining properties
Galling characteristi
cs
suitability for coating
Material of construction
The several materials are available for wear rings according to the Applications.
1. Bronze2. Stainless Steel3. Martensitic stainless steel Bronze is used for wear rings because it exhibits good
corrosion resistance for wide range of water services and tends to wear rapidly when abrasive particles are used. Due to this limitation Stainless steel is used. Martensitic stainless steel wear rings are usually hard and they are more resistant towards wear because of increased surface hardness. Tungsten carbide is used for high hardness and resistant to abrasion
Presenter:Mujadid ul Hassan Khawaja
5.Selection of Pumps
Selection of Pumps
The selection of a pump type for a particular application is influenced by a variety of factors. Such as:
Fluid Characteristics Required material of construction System Flow and Head Requirements Intended Equipment life Energy Cost Availabilty of certain uitlities
1. Pump Types
There are several different types of basic pump designs
Every pump design can be used for a range of flow and head combination
Flow and head range charts for pumps can help in this respect
There are other factors upon which can help us in selecting a suitable pump for a given application
2. Self Priming Requirements
When does the self priming factor becomes important and necessary in pumping????
“If a pump is taking suction from a source below the pump suction nozzle”
Positive displacement pumps are able to self prime within limits in the smaller capacity range
Some special types of centrifugal pumps can also do self priming
3.Variable Head/Flow Requirements
Centrifugal and Axial flow pumps are available to operate in variable head/flow conditions
The head flow range of the pumps can be determined by the their respective pump characteristic curve
This curve gives us information about different characteristics (eg power, NPSH, efficiency)of a pump at different capacity and head requirements..
For a given impeller size, a pump can produce any flow rate within its characteristic curve, if sufficient NPSH is available
3.Variable Head/Flow Requirements
The system head characteristics can be changed to vary flow rate by
Discharge ThrottlingVarying Pump speed
Some pump Characteristic curves are as follows:
3.Variable Head/Flow Requirements
4. High Head Requirement
After selecting the required flow rate, either a centrifugal or a piston pump may fulfill the need for high differential head required.
If a small flow rate is required, either an integrally geared centrifugal pump or a piston pump may be applied
For High flow and high head combinations, a multi stage centrifugal pump can be used.
5. Low Flow with Precise Adjustment Ability
A proportioning pump is appropriate for such application
This type of pump can also be provided with variable flow capacity
Certain types of gears, plungers, diaphragm pumps can also be used in combination with a variable speed drive for flow rate regulation.
NPSHR and NPSHA NPSHR is the amount of liquid pressure required at
the intake port of a pre-designed and manufactured pump.
NPSHA is the amount (A = available) to the pump intake after pipe friction losses and head pressures have been taken into account.
The NPSHA must equal or exceed the NPSHR. The available NPSH is a characteristic of the piping system.
If the NPSHA is lower than the NPSHR then gas bubbles will form in the fluid and caviation will occur.
The NPSHA is calculated from:
6. Low available Net Positive Suction Head (NPSHA)
If the available NPSH is low, specially designed Centrifugal pumps may be used
Depending on how low the NPSH is, either : Horizontal end suction pump with a suction inducer OR A double Suction arrangement may be
applied A vertical Turbine pump may also be used for
this purpose
7. Fluid Characteristics
Is the liquid? Fresh or salt water, acid or alkali, oil,
gasoline, slurry, or paper stock? Cold or hot and if hot, at what
temperature? What is the vapor pressure ofthe liquid at the pumping temperature?
What is its specific gravity? Is it viscous or non-viscous? e. Clear and free from suspended foreign
matter or dirty and gritty?
7. Fluid Characteristics
If the latter, what is the size and nature of the solids, and are they abrasive?
Ifthe liquid is of a pulpy nature, what is the consistency expressed either in percentage or in 1b per cubic ft of liquid? What is the suspended material?
f. What is the chemical analysis, pH value, etc.? What are the expected variations of this analysis?
If corrosive, what has been the past experience, both with successful materials and with unsatisfactory materials
7. Fluid Characteristics
7. Fluid Characteristics
For a highly viscous fluids such as Toothpaste, peanut butter, and shampoos, a positive displacement progressing cavity pump can be used
A rotary variable displacement piston pump might be used for hydraulic control system, but it is not a good choice for potable water application.
For pumping hot asphalt and some other limited applications in lube oil systems, a rotary sliding vane pump can be used.
8. Pump Materials
Material selectin is affected both by 1. The fluid being pumped 2. The environment. Resistance to corrosion and erosion are of
prime importance . The engineer must determine which material
is most suitable for a particular service. Pumps are commonly available in cast iron,
ductile iron, carbon steel, alloy steel, and in some composite materials or special alloys such as Monel, Hastelloy or Titanium.
9. Driver Selection
The choice of driver is as important as the pump selection
Factors affecting the driver choice are:
1. Capital Cost 2. Driver type availability 3. operation reliability 4. Availability and cost of utilities 5. RPM required for the process
6.Metring or Proportioning
And Sizing of Pumps
.
Presenter:Muhammad Belal Malick
Delivery of fluids in precise adjustable flow rates is called metering.
A metering pump is a pump used to pump liquids at adjustable flow rates which are precise when averaged over time.
The term "metering pump" is based on the application or use rather than the exact kind of pump used, although a couple types of pumps are far more suitable than most other types of pumps.
Principle
This class of pumps moves liquids in two stages: the suction stroke and the discharge stroke.(Reciprocating)
The basic principle of metring is to change the displacement per stroke or the stroking speed.
What type of pumps can be metered?
Positive displacement reciprocating pumps can be adapted to function as metring or proportioning devices.
Three basic types of pumps with several variations can be used for this service:
Packed Plunger pump(piston pump) Mechanically actuated diaphragm pump Hydraulically actuated diaphragm pump
Packed Plunger Pump
Mechanically Actuated Diaphragm Pump
Hydraulically Actuated Diaphragm Pump
Capacity Cotrol
Manually adjusted while stopped Manually adjusted while running Pneumatic Electric Variable Speed
Manually adjusted while stopped
Manually adjusted while running
Pump Sizing
Sizing a pump is to figure out the presure required to pump the gallons per minute of fluid.
There are two items required to size a pump:
Fluid flow rate Pressure to be developed
Pump performance curve A Pump Performance Curve is produced by a pump manufacturer from actual tests performed and shows the relationship between Flow and Total Dynamic Head(TDH) or presure.
System Curve
The system curve is a plot of the Total Head vs. the flow for a given systems.
Operating Point
The rate of flow at a certain head is called the duty point. The pump performance curve is made up of many duty points. The pump operating point is determined by the intersection of the system curve and the pump curve as shown in Figure.
Not all system operating points are directly on top of a pump graph or curve as shown below:
It would be best to choose a pump on the curve above the operating point.
If a pump has three speeds then three curves will be shown:
It would be best to operate a pump at a lower speed if possible to prolong the life of the pump and bearings.
PUMPS IN PARALLEL TO MEET VARYING DEMAND
Operating two pumps in parallel and turning one of
when the demand is lower, can result in significant
energy savings. Pumps providing different flow rates
can be used. Parallel pumps are an option when the
static head is more than fifty percent of the total
head.
If W is negative a pump is required; if it is positive a turbine could be installed to extract energy from the system.
The power is given by:
where m = mass flow-rate, kg/s,
η — efficiency = power out/power in.
Power requirements for pumping liquidsThe total energy required can be calculated from the equation:
where W = work done, J/kg,
Δz = difference in elevations , m,
ΔP = difference in system pressures , N/m2,
ΔP= pressure drop due to friction, including miscellaneous losses,
and equipment losses, N/m2,
p = liquid density, kg/m3,
g = acceleration due to gravity, m/s2.
Pump Efficiency
The efficiency of a pump is a measure of the degree of its hydraulic and mechanical perfection.Pump efficiency is expressed in percentage as:
Pump Efficiency =GPM X Total Head X 100/(input HP X 3,960)
HorsePower=HP= A unit of power equal to 745.7 watts.
B.E.P. (best efficiency point)
The pump's efficiency varies throughout its operating range.
The efficiency will depend on the type of pump used and the operating conditions.
The B.E.P. (best efficiency point) is the point of highest efficiency of the pump.
All points to the right or left of the B.E.P have a lower efficiency.
Under sizing of pumps
Undersizing the zones will cause the pump to cycle often.
wears out the motor
excessive overload tripping
Over sizing of Pumps
Operation requires greater NPSH
High pressure drop
Cavitation
Greater power consumption
High purchase cost
Vibration
Keeping in Mind!
Higher Head = Lower FlowLower Head = Higher FlowLower Flow = Lower power
Higher Flow = Higher power
7. Troubleshooting
of Pumps
Presented by:Shahzab Idrees
Suction Problems
Mechanical Problems
System Problems
Hydraulic Problems
Troubleshoots
Troubleshoots in Centrifugal Pumps:
Suction Problems:
Pump not primed Insufficient available NPSH Air leaks into suction line Vortex formation at suction Excessive friction losses in suction line Clogged impeller Selection of pump with too high suction
speed
Troubleshoots in Centrifugal Pumps: Symptoms:
Pump does not deliver liquid Insufficient capacity Requires excess power Vibration Overheating and Seizing Impeller vanes are eroded Corrosion Mechanical seal leaks Coupling fails
Troubleshoots in Centrifugal Pumps:
Hydraulic Problems:
Speed of pump too high/low Wrong direction of rotation Static head higher than shut-off head Total head of system higher/lower than
design of pump Excessive wear
Troubleshoots in Centrifugal Pumps:
Mechanical Problems:
Foreign matter in impeller Misalignment Bent shaft Rotor out of balance Parts loose on shaft Shaft running off-center because of wrong bearings Incursion of hard particles into running clearance Inadequate tightening of casing bolts Pump material not suitable for liquid handled
Troubleshoots in rotary pumps:
Symptoms:
Pump fails to discharge Noisy Wear rapidly Pump starts, then loses suction Takes excessive power
Troubleshoots in rotary pumps: Suction Problems:
Pump not properly primed Suction pipe not submerged Foot valve leaking Suction pipe too small
Mechanical Problems: Pump worn Air leak Pipe strain Corrosion
Troubleshoots in rotary pumps:
System Problems:
Wrong direction of rotation Low speed Insufficient liquid supply Pump runs dry
Troubleshoots in reciprocating pump:
Symptoms
Noise Oil leak Overheated Water in crankshaft Loss of prime Pitted valves
Troubleshoots in reciprocating pump:
Suction problems: Insufficient suction pressure Cavitation Lift too high
System problems: System shooks Overpressure/ overspeed Dirty environment Air in liquid
Troubleshoots in Steam pumps:
Symptoms:
Does not develop rated pressure Lose capacity Vibrates Operation is erratic
Troubleshoots in Steam pumps: Suction Problems:
Suction line leaks Suction lift too high Cavitation
System Problems: Low steam pressure High exhaust pressure Entertained air or vapors
Mechanical Problems: Worn piston rings Misalignment Piping not supported