(Tech Forums)
Pump FAQs
This collection of frequently asked questions is categorized into following categories for your convenience.
Magnetic Drive Pumps / Sealless Pumps
How is hearing wear monitored in sealless pumpes?
Answer: Product lubricated sleeve/journal radial and thrust bearings are typically used in sealless magnetic driven and cannod motor pumps. These bearings are located within a containment shell with no shaft exposed to atmosphere; therefore, they are typically lubricated and cooled by the process fluid. Since the shaft is not exposed to atmosphere traditional proximity probe monitoring of the shaft movement is not easily done. Detection of sleeve bearing wear in sealless pumps can be accomplished by visual inspection and dimensional verification during pump disassembly periods or by special instrumentation while the pump is in operation. Instrumentation used to detect bearing wear falls into two categories, progressive wear monitoring and detection of component contact. Proximity sensing devices can be used to monitor the position of the rotor within the containment device. Positional changes of the rotor are then used to determine the direction and amount of bearing wear. This method permits wear to be detected prior to contact between the rotor and the containment device or other part of the assembly (bearing holder) designed to prevent or limit rotor contact with the containment device. The proximity sensing technologies, when used, are incorporated by the pump manufacturer, and may detect both radial and axial positional changes of the rotor. Progressive wear monitoring is not normally applied to bearings constructed from “nonwearing” materials, such as hard ceramic bearings. Excessive bearing wear or failure of ceramic bearings will allow positional changes of the rotor to cause contact (impacts or rubbing) between the rotor and the containment device or other part of the assembly designed to prevent or limit rotor contact with the containment device. Contact may be detected using a suitable acoustic detection device, power monitor, vibration sensor conditioned to detect impacts and rubhing. containment shell temperature probe, continuity probe, or contact switch.
How is bearing wear monitored in sealless pumps?
Product lubricated sleeve journal radial and thrust bearings are typically used in sealless magnetic driven and canned motor pumps. These bearings are located within a containment shell with no shaft exposed to atmosphere; therefore, they are typically lubricated and cooled by the process fluid. Since the shaft is not exposed to atmosphere traditional proximity probe monitoring of the shall movement is not easily done.
Motor / Electrical
What is an eddy current drive?
An eddy current drive, also known generically as a magnetic drive, eddy current clutch or magnetic clutch, is an electro-mechanical variable speed drive that uses a constant speed motor as the input. The eddy current drive is installed between the motor and the driven equipment. Torque is transmitted to a variable speed output in proportion to a direct current (DC) applied to a set of coils on the output’s rotor. This method of varying speed only reduces the speed of the driven load, which is different than variable frequency drives and DC drives, which vary the speed of both the motor and driven load by electronically altering the input power to motor. Horizontal eddy current drives can either be flange-coupled to the motor or may be separately mounted in a shaft-coupled configuration. In a typical vertical configuration, shown in Image 3, an ordinary induction motor is mounted atop the eddy current drive. The eddy current drive is built within a stationary frame of fabricated or cast steel, with a lower flange and shaft similar to that of a vertical motor. For both configurations, within the frame are two concentric rotating members: the drum, sometimes called the ring, and the output rotor, sometimes referred to as the magnet or field. The drum is a cylinder of magnetically permeable steel coupled directly to the motor shaft, and so rotates at constant speed, determined by the speed of the motor. The variable speed magnetic rotor is mounted concentrically within the drum and is separated by bearings, which maintain an air gap between the inner diameter of the drum and the outer diameter of the magnet to a specified tolerance. The outer surface of the magnet consists of a series of magnetic poles having alternating north and south poles, which are magnetized at varying strength by a low-power DC current, referred to as excitation current.
Why most of the people never recommend the vfd adaptable motor for the suitable specific application., whether its due to non availability or lack of awareness or manufacturers doesn't promote!
In a thermic fluid pump to calculate the drive power, whether to consider the fluid @ ambient temp., or in considering the would be working temperature around 250 to 300 deg. C.
M.Mahendran., B.E.,
kalamegam st., Gobichettipalayam, Erode Dt., T.N.,
1. Lack of awareness – is the plain answer. Very few users or
for that matter consultants specify the VFD for a given application. Cost factor may be one reason or ignorance of the working of VFD and the benefits that will accrue by using it. At the same time, there are cases where VFD specified for an application led to a complete failure! Not because he VFD malfunction but because the user did not know the correct application for a VFD. Common error: User is unaware of the fact that by reducing the speed to half, the output of the VFD controlled motor also reduces to half! A 10 HP at 1450 rpm will just deliver 5 HP at 725 rpm. Customer expected that it will behave like a 10 HP at 725 rpm – with high torque!
2. The difference in the power consumption of pump for thermic fluid will depend only on the difference in the density of the fluid at different temperatures. The difference could be as high as 18% if one compares the densities at 20 deg C vs at 340 deg C! It is better to allow for this extra margin although in the normal working the density will be low and power consumed will be less. An experienced user, who diligently follows the starting procedure will not need this extra margin on the motor as the power consumption with closed discharge valve will be always less than at the duty point.
One can witness cases where the operating head is much lower than specified in the pump data sheet. Consequently, in actual field condition the motor tends to get overloaded as the pump operates at the right of the assumed duty point on the curve! Most often, there is no suction pressure gauge and the discharge pressure gauge is in non-working condition on thermic fluid lines. This makes it difficult for the user to understand the reason for overload!
Why most of the people never recommend the vfd adaptable motor for the suitable specific application., whether its due to non availability or lack of awareness or manufacturers doesn't promote In a thermic fluid pump to calculate the drive power, whether to consider the fluid ambient temp., or in considering the would be working temperature around 250 to 300 deg. C. M.Mahendran., В.Е., kalamegam st., Gohichettipalayam, Erode Dt., T.N..
1. Lack of awareness – is the plain answer. Very few users or for that matter consultants specify the VFD for a given application. Cost factor may be one reason or ignorance of the working of VFD and the benefits that will accrue by using it. At the same time, there are cases where VFD specified for an application led to a complete failure! Not because he VFD malfunction but because the user did not know the correct application for a VFD. Common error: User is unaware of the fact that by reducing the speed to half, the output of the VFD controlled motor also reduces to half! A 10 HP at 1450 rpm will just deliver 5 HP at 725 rpm. Customer expected that it will behave like a 10 HP at 725 rpm – with high torque!
2. The difference in the power consumption of pump for thermic fluid will depend only on the difference in the density of the fluid at different temperatures. The difference could be as high as 18% if one compares the densities at 20 deg C vs at 340 deg C! It is better to allow for this extra margin although in the normal working the density will be low and power consumed will be less. An experienced user, who diligently follows the starting procedure will not need this extra margin on the motor as the power consumption with closed discharge valve will he always less than at the duty point.
One can witness cases where the operating head is much lower than specified in the pump data sheet. Consequently, in actual field condition the motur tends to get overloaded as the pump operates at the right of the assumed duty point in the curve! Most often, there is no suction pressure gauge and the discharge pressure gauge is in non-working condition on thermie fluid lines. This makes it difficult for the user to understand the reason for overloud!
Reciprocating pumps
How can I determine the pump input power for a reciprocating pump?
Pump input power may be determined by transmission dynamometers, torsion dynamometers, strain gauge type torque-measuring devices, calibrated motors or other sufficiently accurate measuring devices.
When applicable, readings of power shall be taken at the same time that rate of flow is measured.
Methods of measurement of power input to the pump fall into two general categories:
Those which determine the actual power or torque delivered to the pump and are made during the test by some form of dynamometer or torque meter;
Those which determine the power input to the driving element, taking into account the driver efficiency when operating under specific conditions.
When pump input power is determined by transmission dynamometers, the unloaded dynamometer shall be statically checked prior to the test by measuring the load reading deflection for a given torque; and by taking the tare reading on the dynamometer scale at rated speed with the pump disconnected. After the test, the dynamometer should be rechecked to assure that no change has taken place. In the event of a change of± 0.5% of the power at the best efficiency point (BEP), the test should be rerun. An accurate measurement of speed within ± 0.3% is essential. The use of calibrated dynamometers or motors is an acceptable method for measurement of input power to the pump.
Calibration of the torsion dynamometer should be conducted with the torsion-indicating means in place. The indicator should be observed with a series of increasing loadings and then with a series of decreasing loadings. During the taking of readings with increasing loadings, the loading is at no time to be decreased; similarly, during the decreasing loadings, the loading should be based on the average of the increasing and decreasing loadings as determined by the calibration.
If the difference in readings between increasing and decreasing loadings exceeds 1%, the torsion dynamometer shall be deemed unsatisfactory.
Dynamometers shall not be employed for testing pumps with a maximum torque below one-quarter of the rated dynamometer torque. When strain gauge type torque measuring devices are used to measure pump input horsepower, they shall be calibrated, with their accompanying instrumentation, at regular intervals After the test, the readout instrumentation balance shall be rechecked to assure that no appreciable change has taken place. In the event of a change of ± 0.5% of the power at BEP, the test shall be rerun.
Calibrated electric motors are satisfactory to determine the power input to the pump shaft. The electrical input to the motor is observed, and the observations are multiplied by the motor efficiency to determine the power input to the pump shaft.
Calibrated laboratory type electric meters and transformers shall be used to measure power input to all motors.
Can reciprocating pumps be used as booster pumps?
A booster for a reciprocating power pump is normally a centrifugal pump but may be a positive displacement pump under special conditions (see item 4 below). Care must be exercised in the selection and installation of a booster pump. because improper selection and/or installation can result in increased pulsations and attendant problems. Here are some recommendations: 1) Install a booster pump as close to the inlet source as practical; 2) The booster pump must add enough pressure to the system to provide sufficient Net Positive Suction Head Available (NPSHA) to the power pump, allowing for acceleration head, friction losses and pressure pulsations due to acoustical resonances; 3) Install a pulsation dampener in the inlet line adjacent to the power pump liquid cylinder. Consult dampener and pump manufacturers for proper location of the device. The dampener can often be omitted between a centrifugal booster pump and a low-speed power pump under any of the following conditions: i) Diameters of inlet and outlet connections of a booster pump are equal to, or larger than, inlet connection on power pump: ii) Diameters of all piping between liquid source and power pump are equal to, or larger than, inlet connection of power pump; iii) The booster pump is sized for maximum instantaneous rate (Courtesy Hydraulic Institute)
Pumps & Systems
What are some methods for monitoring corrosion in a pump?
Corrosion in pumps is a serious concern for users that can lead to catastrophic failure of a pump if it is not properly monitored. Selecting the proper material for the pump is extremely important in addressing this concern. Material selection depends on numerous conditions such as the fluid being pumped or speed of rotation of the pump. Choosing the incorrect material for an application will accelerate the effects of corrosion. Similarly, choosing the best-suited material for an application will dramatically reduce the effects of corrosion. Because of the dangers of corrosion in pumps, it is necessary that pumps applied in systems where corrosion is a known risk are frequently checked to ensure normal operation.
Several methods for corrosion monitoring exist.
A visual inspection of the pump is the easiest and can reveal corrosion damage occuring in the pump. A drawback to a visual inspection is that it requires the pump to be off and taken apart. Additionally, stress cracking could have no visible signs in the visual check, yet the results can be sudden and catastrophic.
General corrosion can be detected by using a metal probe to measure the electrical resistance. As the cross section is reduced by corrosion, the measured electrical resistance will increase.
Metal probes can also be used to measure the linear polarization resistance. A voltage is applied using the probes and the resulting current is proportional to corrosion rate.
Finally, ultrasonic thickness measurement can determine the thickness of an area on the pump and show if thickness is being lost due to corrosion.
What should end users consider in the selection of wetted parts for pumps based on the temperature of the liquid being pumped?
The handling of liquids at temperatures below 32 F (0 C) or above 250 F (120 C) usually requires careful selection of the materials and corresponding attention to construction details. The corrosion-resistance and/or physical properties of many of these materials are affected by high or low temperatures.
For this reason, end users must consider the temperature of the liquid being pumped.
For material selections acceptable in the temperature range involved, consult the applicable codes and practices of the industry in which the pump will be used. Selection of materials for pumps operating at low temperatures should be made only after each component and its function have been considered.
Many materials change from tough to brittle behavior with a decrease in temperature.
As a starting point in the selection of a suitable ferric steel for low-temperature service, the user may consider a heat-treated, fine-grain, low-carbon alloy steel with moderate hardness and low phosphorus, nickel and molybdenum. This material usually offers better notch toughness at low temperatures than other ferric steels.
Users should also consider the austenitic stainless steels and bronzes for possible use in low-temperature pumping applications. Austenitic stainless steels, fully annealed, show improving toughness with decreasing temperature, and they exhibit no transition point. Most bronzes and all aluminum alloys are not embrittledat low temperatures, and they may also serve in this type of service, if otherwise suitable for the application.
Other considerations, such as cost, corrosion-resistance availability, erosion-resistance, hardness, toughness and fatigue strength, must be carefully considered before the final selection of materials for high- or low-temperature services can be made. Also note that other factors should be considered when selecting materials for wetted pump parts, including the user’s experience, the manufacturer’s experience, the expected pump life (such as temporary or long-term use), whether or not it is intermittent or continuous duty, pumping hazardous or toxic liquids, and the condition of the liquid.
What are the best materials to use in pump construction to minimize part corrosion?
Pumps are produced using a wide variety of materials. Factors that must be considered in the selection of materials for wetted pump components include user’s experience, life cycle costs, regulatory agency requirements (i.e. limits on lead content in bronzes that contact drinking water), required pump life, duty cycle (operating hours per period), corrosive and/or erosive properties of the fluid, hazardous nature or toxicity of the fluid, the potential for cavitation and the potential for contamination of the fluid. Corrosive and/or erosive properties of fluids may vary with temperature, concentration of chemicals or solids, the properties of the solids, velocity, and the extent of entrained gasses.
Some of the more frequently used materials are listed below.
▸Bronze-fitted pump: The casing is made of cast iron, and the impeller and impeller rings are made of bronze. This combination is commonly used for fresh water at ambient temperatures.
▸All bronze pump: All parts of the pump in direct contact with the pumped liquid are made of manufacturer’s standard bronze. This type of pump is often used for pumping seawater. All iron pump: All pump parts in direct contact with the pumped liquid are made of ferrous metal (cast iron/ductile iron, carbon steel or low-alloy steel). This pump is commonly used in hydrocarbon services and some chemical applications.
▸ Stainless-steel fitted pump: The casing is made of materials
suitable for the service. The impellers, impeller rings and shaft sleeves (if used) are made of corrosion-resistant steel with suitable properties for the specific application. This type of pump is also used in hydrocarbon and chemical services.
▸ All stainless-steel pump: All pump parts in direct contact with the pumped liquid are made of corrosion-resistant steel with suitable properties for the specific application. This pump is commonly used in chemical applications.
Rigid polymers/composites All pump parts in direct contact with the liquid are made of rigid polymers or composites (plastics), either as coatings or as structural material. This pump type is commonly used in chemical services.
(Courtesy: Hydraulic Institute)
While selecting Boiler feed pumps how much margin one should consider for discharge head and flow. Manager, Cogeneration Hindalco Ind Ltd Renukoot, Sonebhadra
When the evaporation rate is known correctly, the catch-up capacity can be determined as follows:
For boilers with modulating feedwater control system: add 25 % to evaporation rate.
For Boilers with on-off control: add 100% to evaporation rate.
The Evaporation rate should include system load + blowdown +steam rate to Dearator
Feed water rate Evaporation rate + catch-up capacity
if the unit is kg/hr, divide by 960 to get flow rate in m3/hr
The other prevelant practice is to use Boiler HP as a base to calculate the Feed Water rate.
A margin of 15% as a safety factor is applied over this feed rate.
BHP x 0.01568 = feed rate in m3/hr.
To this one must add the min flow rate of the pump as recommended by Pump manufacturer.
If this is unknown use 15% margin on the Feed rate of pump obtained.
Example: 1000 Hp Boiler
Pump feed rate Boiler = HP x 0.01568 m3/hr
= 1000 x 0.01568
= 15.68 m3/hr
SF of 15% on this.
Qpump1.15 x 15.58
17.917 m3/hr
Add min flow requirement as per pump manufacturer’s recommendation to this for specifying the flow rate of pump. If the manufacturer’s recommendations are not at hand use 15 % of Qpump calculated above.
Thus the Q total 17.917+15% of 17.917 17.917+2.688 20.605 m3/hr
The operating head should be calculated correctly considering the following:
1) Safety valve set pressure +3%
2) loss across NRV
3) piping loss to boiler
4) drop across the level control valve (not needed in case o on-off control)
5) pressure drop in the discharge line
Total pressure divided by density (consider 0.96, if unknown) and ‘g’ will give Head im ‘mWe’
For details on the subject, refer to ASME Boiler codes
What is acceleration head and how can it impact pump performance?
Acceleration head or pressure is a system phenomenon associated with both direct acting pumps and reciprocating power pumps, due to the acceleration and deceleration of the liquid in the suction piping of these types of pumps.
Acceleration head or pressure is often thought of as being a loss, and it is treated as such when calculating NPSHA; but the pressure drop caused by the acceleration is offset by the increase in pressure when the liquid decelerates. Therefore, the average pressure in the suction line is calculated without consideration of acceleration head.
Total suction lift represents the average without reference to the fluctuations above and below this average due to the inertia effect of the liquid mass in the suction line. With higher speed of the pump or with relatively long suction lines, this pressure fluctuation or acceleration head must be taken into account if the pump is to fill properly without cavitation, pounding or vibration of the suction line.
The low speeds of direct acting pumps normally keep acceleration head low enough for satisfactory operation However, it is desirable to perform an acceleration head calculation to ensure proper pump operation is obtained.
With a direct acting pump, maximum piston or plunger acceleration occurs at the start or the end of each individual stroke. This is reflected in a similar discontinuity in the cyclical pattern of the combined flow curve corresponding to each piston or plunger. The head required to accelerate the liquid column is a function of the length of the suction line, the average velocity in this line, the pump speed, pump type, and the relative elasticity of the liquid and pipe.
There is a similar pressure fluctuation on the discharge side of every direct acting pump, but it cannot be analyzed as readily because of the pressure influence on liquid and piping elasticity plus the smaller diameter and much greater length of the discharge line in most applications. However, a pulsation dampener can be just as effective in absorbing the flow variation of the discharge side of the pump as on the suction side and should be used if low-frequency pressure fluctuation or piping vibration is a problem.
I would like to know the difference between abrasion and corrosion. What type of M.O.C for impeller and shaft is suitable for abrasion and corrosion? Amitava Bandyopadhyay, Kolkata
One commonplace example of understanding the difference is water laden with sand. Sand, per se, is not corrosive, but it is very abrasive. Conversely acid with no entrained solids, clear acid, will not be abrasive but highly corrosive. Sea water will also be corrosive. But corrosion due to sea water is due to its alkalinity whereas corrosiveness of acids is acidic in nature. MOC for corrosion resistance has to take into consideration whether the corrosiveness is acidic or alkaline. Abrasion is also of two types. Abrasion due to fly ash in power stations will be from fine particles moving too close to the surfaces and abrading the surfaces. Abrasion due to sand particles or coal particles will be due to the particles hitting hard on the surface and bouncing back and hitting repeatedly. This is rather erosion than abrasion. So nature of abrasive wear depends upon the angle of incidence of the particles w.r.t. the surface. Usually hard surfaces would take abrasive wear better and resilient surfaces such as elastomer-linings would take the erosive wear better. But this is too much of a thumb rule. One needs to study the wear patterns and refer to the data available in handbooks.
Sir, let me correct, it's an underground tank, with pumps position are also installed underground nearby room in such a way suction inlet taken as flooded. It's [1W+18]. Pipeline detail mentioned refer to discharge side. Sir, suction pipeline is 400mm, individual. No header is installed.
That makes a big sense. That’s why a sketch makes a better communication tool. Use it in future!
Let me work out the probable performance at rated speed
400 mm dia individual suction line is a very well thought of.
So suction should not be a problem.
A compound gauge on pump suction helps: a reading before the pump is switched on and next reading when the pump is switched on helps to see if there are any instructions in the suction valve ete.
If you have such readings-they will help.
We should rule of nothing during analysis.
A centrifugal pump will deliver flow rate exactly as per the intersection of pump performance graph and the system (resistance) curve.
If you have the performance curve from the manufacturer for 1480 rpm, you can draw curves for 1374 rpm as well as 1260 rpm. The shut off head will decrease in the ratio of the square of the speed.
e.g. at 1374 rpm, it will decrease by a factor of (1480/1374)^2 -1.26
Hence the new shut off head will be (52/1.26)-42.26 m. Shut off head is independent of how many identical pumps are working in parallel.
If the VFD has been set not to exceed a particular value of the current, then it will automatically adjust the speed to stay within the current limits. You can try bypassing the VFD and note the performance at 1480 rpm. This will give you a clue.
How accurate is the flow measurement?
The pipeline resistance is very small. At 600 cu.mtr/hr in a 12″ line it is just 1.5 m/100m. The max friction head loss be around 10 m. Together with static head of 31 m, the total head will be 41 m only.
Lastly, chock the actual impeller dia installed in the pump. If the dia is correct, the shut off head should be as per what is shown in graph at rated speed.
Cheek if someone has set the current limit on VFD. This may be restricting the motor speed.
If at all you want to set it let it be as per the motor FLC+5%. Try operating the pump without (by passing) VFD to see if you get the required performance. Pipelino size selection is OK. Just 1.5 m/100 m loss at 600 cu.mtr/hr Ask pump supplier to provide curves for actual speeds observed. You can also draw provided you have a curve at 1480 rpm. Share the result after VFD by-pass.
Detection of sleeve bearing wear in sealless pumps can be
accomplished by visual inspection and dimensional verification during pump disassembly periods or by special instrumentation while the pump is in operation. Instrumentation used to detect bearing wear falls into two categories, progressive wear monitoring and detection of component contact.
Proximity sensing devices can be used to monitor the position.
of the rotor within the containment device. Positional changes of the rotor are then used to determine the direction and amount of bearing wear. This method permits wear to be detected prior to contact between the rotor and the containment device or other part of the assembly (bearing holder) designed to prevent or limit rotor contact with the containment device. The proximity sensing technologies, when used, are incorporated by the pump manufacturer, and may detect both radial and axial positional changes of the rotor. Progressive wear monitoring is not normally applied to bearings constructed from “nonwearing” materials, such as hard ceramic bearings.
Excessive bearing wear or failure of ceramic bearings will allow positional changes of the rotor to cause contact (impacts or rubbing) between the rotor and the containment device or other part of the assembly designed to prevent or limit rotor contact with the contamment device. Contact may be detected using a suitable acoustic detection device, power monitor, vibration sensor conditioned to detect impacts and rubbing. containment shell temperature probe, continuity probe, or contact switch. water mixture, beyond a threshold limit, that reaches the sensor.
In an inner seal of a dual unpressurized seal arrangement, change in the seal reservoir pressure can be detected by either blocking off the reservoir from the vent and noting the increase in pressure or using a pressure transmitter or switch. In an inner seal of a dual pressurized seal arrangement, change in the scal support system pressure can be detected by using a pressure transmitter or switch.
want to know the steps taken in a pumping system to attain the desired operating point for the system when.....
(a) the pump is driven by a fixed speed motor and,
(b) when the pump is driven by either a variable speed motor or a turbine.
Osita Okeke
on e-mail
The operating point is the point of intersection between the H-Q curve of the pump with the H-Q curve of the system. Once a pump is set into a system, this will happen automatically. But if the operating point, which happens automatically is not the ‘desired’ operating point, one has to modify either the pump curve or the system curve.
There are two ways to modify the pump curve –
1) Change the speed of the pump
2) Change the diameter of the impeller of the pump
3) The system curve can be notified by modifying the system. This is usually done either by changing the setting of the delivery valve or one can change it also by revamping the system by changing the pipe-sizes and/or layout of the piping.
4) If the suction conditions in the system are prone to cause the pump to cavitate, modifying the system to eliminate cavitation will also modify the pump curve from a cavitating condition to non-cavitating condition. 5) For changing the speed of the pump (option I above), changing the driver from an electric motor to a turbine will often become changing from a low-speed driver to high-speed driver.
Such change is possible even by using a gearing or pulley mechanism between the pump and the motor. But at increased speed the pump demands higher power input. So, it becomes important to check whether the motor has adequate margin in power. No such caution is needed if “desired” operating point is obtainable by reducing the speed.
For determining the required speed at the “desired” operating point, say
(Q”,H”)one needs to find the point (Qo, Ho) on the pump curve H=a^ * Q ^ 2 +b^ * Q+c which also is a point on the parabola through the origin and ( Q ^ prime prime ,H^ prime prime ) The equation of this parabola will be H=k^ * Q ^ 2 , where k-H”/(Q”)^2.
Since (Qo, Ho) is to be a point both on H=k^ * Q ^ 2 and H=a^ * Q ^ 2 +b^ * Q+c
to find (Qo, Ho) one needs to solve the quadratic (a – k) * (Qo) ^ 2 +b^ * Qo+c=0
Actually all the mathematics starts with knowing the values of the co-efficients a, b, c for the pump curve H=a^ * Q ^ 2 +b^ * Q+ e This is not difficult, if one knows three points on the curve, say, (0, Hso), (Q1, H1) and (Q2, H2) and solves simultaneous equations. A simpler way to do this is to plot the pump curve in an Excel spreadsheet and fit a “trendline”, setting also the option for the display of the equation of the polymonial of degree 2.
How is the public water supply treated and made safe for consumption?
Answer: Disinfection of treated water is the fi nal step in a water treatment plant (not to be confused with wastewater treatment plants), which ensures that the water is safe for human consumption. Chlorination is one of the most common forms of disinfection due to its lowcost and history of eff ectiveness. With this process chlorine gas is fed into the water using a gas chlorinator/injector to control dosage, while sodium hypochlorite is dispensed to each point of application using a metering pump to control dosage. The chlorine is delivered in pressurized cylinders in a liquid form, and is converted to gas as the pressurized liquid discharges at a lower pressure.
Treated water is stored in the chlorine contact tank which is also called the clearwell (Figure 3). Final treatment occurs at the end of the chlorine contact tank after water has been fully disinfected. At this point, water quality is considered potable and ready for human consumption, despite trace levels of chlorine being present.
Sir, in an industry the cooling liquid is fed by a pump to the finishing machine for fine tuning the finished moulds. The cooling liquid contains zirconia, alumina, silica, soda, the centrifugal pump self priming type wetted parts in cast iron is used which gets eroded quickly, and client been trying alternate of aodd type with body in aluminium which also gets eroded and invites constant spares replacement in dedicating manpower exclusively for the work. Theoccurance leads to downtime, and financially consumes a part of the maintenance allotment.is peristaltic pump is suitable ?, kindly request for yours suggestion and the moc suitable M.Mahendran, Gobichettipalayam, Erode dt., TN
Question relates to handling of cutting fluid with abrasive particles. OEM of such machines, usually selects a pump based on the suitability for the duty.
Replacing a centrifugal pump with a PC pump may sound like a good idea when one reads what a PC pump can do. It will be like a panacea to a customer riddled with recurring parts replacement in a centrifugal pump! Fine ground particles of Zirconia and other abrasives have higher density that the carrier fluid. These particles settle down unless they move a velocity higher than settling velocity. The latter depends on SG of solids, size of the particle, viscosity and density of the carrier fluid.
Usually, solid particles are separated by using a hydrocyclone, remaining fluid passes through a filter pressure before the clean cutting fluid is sent to a grinder post.
Appropriate metallurgy for the key components like casing, impeller and shaft wear sleeve is the key to optimum performance. High Chrome steel, Nihard cast iron, high manganese steel parts are often employed. Pumps must be specifically designed for abrasive duty.
Study the literature of manufactures like Schlamenbeger, Wilfley, GIW (now KSB), Metso and others for such applications.
PC pumps are used when the flow rates and operating speeds permit their usage.
Slow speed generally means reduced wear but in a PC pump this is not always true.
At lower rotor speeds, solids tend to settle down in the stator cavity. Constant rubbing of rotor on these settled particles causes a rapid wear on rotor surfacce while stator will show almost no wear at the 6 O’ clock position!
Replacing a centrifugal pump with a PC pump is not always a good idea. Past issues of Pump India carried articles on slurry handling. If possible, go through them again. For specific recommendations, share the duty conditions, pump used, speed of operation, life of components to see if it is worth considering a PC pump as a replacement.
Process Pumps
What should be considered when designing a piping system for process pumps?
Many pipe specifications have sizing rules to aid in the selection of the optimum pipe diameter. The sizing rules can be based on achieving an optimum average fluid velocity in a pipe run for the design flow rate, or a specific pressure drop per unit pipe length. The pipe run sizing rules are trade-offs by: o Choosing a small pipe diameter to minimize construction cost o Choosing a large pipe diameter to minimize pipe run friction loss and pumping cost The value for the optimum pipe diameter is based on the cost of the piping versus the cost of pumping power. If the pipe diameter is below the optimum diameter, then the cost of the piping is reduced, but the friction loss in the pipe run increases, which results in higher pumping cost. If the pipe diameter is greater than the optimum, then there is less friction loss in the pipe run, resulting in lower pumping cost, but higher construction costs. Determining the optimum pipe diameter requires a cost analysis for the life cycle of the plant. If it’s known for certain that the capacity of the existing system will increase, then it’s possible to compare the additional cost of sizing the pipe run for future loads against the cost of adding parallel pipe runs to the system at a later date to accommodate increased capacity in the future. A trade-off in pump system design elements affects both initial A trade-off in pump system design elements affects both initial and life cycle cost. A number of life cycle costs depend directly on the diameter and the components in the piping system (i.e., initial cost, energy cost, and maintenance cost).
Much of the pressure loss in the system is caused by valves, in particular control valves in throttle-regulated installations. In systems with several pumps, the pump workload is divided between the pumps, which, together and in conjunction with the pipe system, deliver the required flow.
The piping diameter is selected based on the following factors:
o Economy of the whole installation (pumps and system)
o Required lowest flow velocity for the application (e.g., to avoid sedimentation)
o Required minimum internal diameter for the application (e.g., suitable for solids handling)
o Maximum flow velocity to minimize erosion in piping and fittings
o Plant standard pipe diameters
Decreasing the pipe run diameter has the following effects:
o Initial costs of piping and components typically decrease.
o Initial costs of pump increase because of increased flow losses with consequent requirement for higher head pumps and larger motors. Costs for electrical supply systems therefore will increase.
o Energy costs will increase because of higher power usage caused by increased friction losses.
Some costs increase with increasing pipe run size, while other costs decrease. An optimum pipe run size, therefore, may be found based on minimizing costs over the life of the system.
My query is how do we decide when we should go for API pump and when for Non-API pump? If we select a Non-API pump, then there are a large number of design standards available (IS, ISO, ANSI, etc.). Which one to specify and when? Aditya K. Golwalkar Reliance Industries Limited
Myriad of standards makes the choice difficult for anyone.
But with a little help and understanding, we can segregate the wanted from unwanted.
API is one standard that has become fashionable these days. The ironical part is that it is specified for duties that has nothing to do with hydrocarbon processing.
Basically written for use in refineries where the duty is 24 x 7 x 365 keeping reliability and ease of maintenance in mind, this is being used where it has no relevance.
Positive displacement Pumps
What information is available regarding NΡΙΡΑ and NPIPR for rotary pumps?
Net positive inlet pressure available (NPIPA) is the algebraic sum of the inlet and barometric pressure minus the vapor pressure of the liquid at the inlet temperature: This value must be equal to or greater than the net positive inlet pressure required (NPIPR) as established by the pump manufacturer for the speed, pressure and fluid characteristics that exist. Otherwise, the rate of flow will be reduced, and operation may be noisy and rough because of incomplete filling of the pump. This condition may damage the pump and the associated equipment. It must be recognized that many rotary pumps can stably and quietly operate at rate of flow reductions of 20 percent to 3 percent because of low NPIPA with no ill effect. Many services use this reduced rate to operate high-vacuum systems for the extraction of gas or light liquids. NPIPR is the pressure required above liquid vapor pressure to fill each pumping chamber or cavity while open to the inlet chamber. It is expressed in bar (psi). NPIPR is sometimes called NPSH3 for rotodynamic pumps. Many liquids handled by rotary pumps have an unpredictable or very low vapor pressure. Most of these liquids have entrained and dissolved gas (frequently air) as well. The practical effect of dissolved and entrained gas is to increase the NPIPR to suppress the symptoms of cavitation. While true cavitation occurs if the liquid reaches its vapor pressure during the filling of the pumping cavities, most of the cavitation symptoms will be exhibited before reaching liquid vapor pressure. This is largely because the entrained and dissolved gas expands when subjected to reduced pressure. Because the level of dissolved gas is a function of the liquid and its temperature and the level of entrained gas is a function of system design and operation, NPIPR for a rotary pump is difficult to establish with precision. NPIPR tests are normally conducted by the manufacturer in a test environment that minimizes entrained gas using a test liquid of negligible vapor pressure. NPIPR is established at the first indication of the following: A 5-percent reduction in output rate of flow at constant differential pressure and speed A 5-percent reduction in power consumption at constant differential pressure and speed The inability to maintain a stable differential pressure and speed The onset of loud or erratic noise when this criterion is previously agreed upon by all parties
Centrifugal pumps
What is the relation between pressure and velocity? How it function on centrifugal pumps ? Enamuthu Sankaran Techno Pro Traders and Contracters Co WLL. Doha, Qatar
A moving fluid has hydraulic energy, which comprises three components, viz. potential energy, pressure energy and kinetic energy. If flow cross-section changes on a horizontal pipeline, say, if it reduces, the potential energy will remain the same, the kinetic energy (i.e. velocity) will increase and the pressure energy will reduce. Conversely, if the cross-section increases, the kinetic energy reduces and the pressure energy increases. Between two cross sections, there will also be loss of energy due to hydraulic friction. The loss of energy is proportional to square of velocity. So, to contain the loss of energy, it becomes advisable to have low velocities by having broad cross-sections. In pumping systems, this concept advocates use of broad cross-sections of pipes.
In centrifugal pumps, the impeller imparts kinetic energy. For availing the most benefit of the kinetic energy imparted by the impeller, it becomes necessary to convert the kinetic energy into pressure energy. This is achieved in the volute casing or bowl or diffuser of the pump, which has gradually increasing cross-sections. That makes the outline of the cross-sections of the volute around the impeller into an Archimedean spiral Because of this, the volute casing is also called as Spiral Volute Casing.
In an ETP [effluent teatment plant of an industry, in Aeration tank/Equalisation tank to control parameters like BOD, COD etc., we infuse air into the effluent by placing disc diffusers as required @ the bottom of the tank, air being generated by blower. In this tank i place a centrifugal pump with -ve suction, is the air will be sucked by the pump and inturn drop in flowrate ? if its so what should be done., M.Mahendran, Gobichettipalayam, Erode dt.,
Air Diffusion is a common method to control BOD and to some extend COD.
If you have an intake from this tank no matter where you place your intake pipe air is bound to find its way into
pump suction. The pump flow rate will drop sharply as a result. If the pump is not of self venting type eventually it will get air-locked and lose prime.
If you have to place the inlet with in the tank try the following:
Make a compartment in the tank in such a manner so that this section is not directly in the path of rising air bubbles. Further place a wire mesh screen across the width of a tank. The top portion of the screen should be about 2″ above the highest level of water while the lower portion can be at about 6″ from the bottom of the tank. Wire mesh effectively keeps the air from crossing over to the pump intake.
One more unconventional but effective way to reduce the air intake at suction is to reduce the suction velocity.
An inverted funnel attached to intake pipe increases the suction area several folds. The velocity gets reduced in the same ratio. Air bubbles will not travel downwards due to buoyancy unless the suction velocity is high.
What types of pump losses can be expected with the increase of liquid viscosity in a rotodynamic pump?
When the viscosity of the pumped liquid increases, the Reynolds number decreases causing friction factors in the hydraulic passages of the pump to increase just like flow through a pipe. Two examples of pump losses that can be anticipated are mechanical and hydraulic losses. Mechanical losses are essentially independent of the viscosity of the liquid being pumped. Hydraulic losses-similar to pipe friction losses-occur at the inlet, in the impeller, in the volute or diffuser, and in the discharge of a pump. In basic rotodynamic pump theory, the useful head is the difference of the impeller theoretical head minus the hydraulic losses. Viscosity does not generally influence the flow deflection or slip factor of the impeller. As a result, the theoretical head is not affected. Head reduction due to viscous flow is primarily a function of the hydraulic viscous flow losses. These hydraulic losses consist of friction losses, wh are a function of the Reynolds number (pump Q + size, rotor speed and wiscosity effects), surface roughness of the hydraulic passageways, and mixing losses caused by the exchange of flow momentum due to non-uniform velocity distributions. Such non-uniformities or mixing losses are caused by the action of work transfer from the blades, decelerations of the liquid, angle of incidence between liquid flow and blades, and local flow separations.
What is a chopper pump?
Chopper pumps are centrifugal pumps with the capability to handle fluids with a high concentration of solids. Chopper pumps have a cutting attachment added made of hard materials of fixed and rotating elements that macerate solids before entry to the impeller that allows it to handle difficult materials. They cut solids so they pass through the pump more easily and flow out with the rest of the pumped fluid.
A chopper pump’s ability to handle solids gives them more flexibility in what they can pump; this characteristic makes them particularly useful in wastewater treatment plants. Wastewater treatment is split into primary treatment and secondary treatment. Primary treatment is the physical separation of float-able materials and insoluble solids from the wastewater. Secondary treatment is biological treatment of water using microorganisms to remove the remaining solids in the fluid. Both treatments contain solids in the pumped fluid and may require chopper pumps.
Specific steps in the process include pumping scum, mixing the contents of the aeration basin and the anoxic zone, and pumping sludge.
A typical centrifugal pump impeller is more easily clogged by solids, which can halt pumping and cause damage to the system. In particular, stringy materials found in wastewater during the treatment process is especially troublesome to normal centrifugal pumps as the material can tangle the impeller. However, the chopper pump is more effective in dealing with this issue.
Air Operated Diaghphram Pumps
How is the performance of air-operated diaphragm pumps affected by the viscosity and specific gravity of the liquid?
A pump manufacturer’s published data is normally based on testing with water. The supplied air pressure, pump flow rate, the net positive inlet pressure (NPIP)/net positive suction head (NPSH) and the pumping system determine the discharge pressure for a given air-operated diaphragm/bellows pump.
Liquids with viscosity below 500 centipoise do not usually affect manufacturers’ published pump performance data. As viscosity increases above this value, the possibility of liquid cavitation increases, and drops in pressure across pump components-particularly the suction check valves-raise the required NPIP/NPSH significantly. Specific gravity can also affect the pump suction performance.
A liquid with a high specific gravity will reduce the manufacturer’s published data on suction-lift capabilities.
Viscous liquids tend to impede efficient check valve operation, which can result in a reduced flow rate. This condition is caused by delayed check valve seating and reverse liquid flow.
End users should carefully determine the nature of the liquid being pumped. Non-Newtonian or shear-sensitive liquids may have pumping characteristics unrelated to those of Newtonian liquids with similar quiescent viscosity. Apparent viscosity for an application using a non-Newtonian liquid can be adjusted based on flow rate conditions for the application by consulting the material manufacturer’s shear rate versus shear stress diagram for the specific material
Submersible/VT pumps
What is the reason for rubber diaphragm of submersible motor to damage?
Rubber diaphragm of the submersible motor is to provide extra volume, needed for water in the water-filled motor to expand, when water experiences rise in temperature. Frequent fluctuation of the diaphragm is prone to induce hysterisis and cause work-hardening of the rubber. Work-hardening is liable to make the rubber brittle and in turn suffer rupture. If the fluctuation of the rubber between expansion and contraction is at a high frequency, the fatigue of such high frequency will hasten the hysterisis, work-hardening and damage
How can seal leakage be monitored in submersible pumps?
The two principal places for lenkage monitoring are at the bottom of the motor (for vertical shaft motors) or in the seal barrier fluid containment volume. Two sensor types dominate the market: the conductivity probe and the float switch. In order to detect liquid intrusion from all possible areas, it is beneficial to install the leakage sensor in the bottom of the dry motor compartment.
The float switch contains a small floating element. Under normal conditions, it rumains at rest at the bottom, but when liquid enters, it rises. This rise can be detected by several electrical methods. While reliable, float switches are position sensitive, so they are usually not used in submersible equipment that is subject to incline, such as in portable pumps The conductivity probe senses the conductance of an oil-water mixture, beyond a threshold limit, that reaches the sensor In an inner seal of a dual unpressurized seal arrangement, change in the seal reservoir pressure can be detected by either blocking off the reservoir from the vent and noting the increase in pressure or using a pressure transmitter or switch. In an inner seal of a dual pressurized seal arrangement, change in the seal support system pressure can be detected by using a pressure transmitter switch
How can seal leakage be monitored in submersible pumps?
The two principal places for lenkage monitoring are at the bottom of the motor (for vertical shaft motors) or in the seal barrier fluid containment volume. Two sensor types dominate the market: the conductivity probe and the float switch. In order to detect liquid intrusion from all possible areas, it is beneficial to install the leakage sensor in the bottom of the dry motor compartment.
The float switch contains a small floating element. Under normal conditions, it rumains at rest at the bottom, but when liquid enters, it rises. This rise can be detected by several electrical methods. While reliable, float switches are position sensitive, so they are usually not used in submersible equipment that is subject to incline, such as in portable pumps The conductivity probe senses the conductance of an oil-water mixture, beyond a threshold limit, that reaches the sensor In an inner seal of a dual unpressurized seal arrangement, change in the seal reservoir pressure can be detected by either blocking off the reservoir from the vent and noting the increase in pressure or using a pressure transmitter or switch. In an inner seal of a dual pressurized seal arrangement, change in the seal support system pressure can be detected by using a pressure transmitter switch
How can we determine the proper size for the intake sump to accommodate several vertical turbine pumps taking input from a river?
The basic design requirements for satisfactory hydraulic performance of rectangular intake structures include adequate depth of flow to limit velocities in the pump bays, reduction of the potential formulation of surface vortices, and adequate pump bay width to limit the maximum pump approach velocities. The pump bay width should be narrow and long enough to channel uniform flow toward the pumps The minimum submergence (S) required to prevent strong air core vortices is based in part on the Froude number-a dimensionless flow parameter with consistent units-defined as:
FD-V/(gD)0.5
Where:
FD-Froude number (dimensionless)
V Velocity at suction inlet equals the flow per unit area based on D
D-Outside diameter of bell or pipe inlet
g-Gravitational acceleration
The minimum submergence with units consistent with the outside diameter of the bell or pipe inlet can be calculated using the formula:
S-D(1+2.3FD)
There is some variation in bell velocity among pump types and manufacturers. However, variations in bell inlet velocity are secondary in maintaining acceleration of flow and converging streamlines into the pump bell.
The effectiveness of the recommended pump bay dimensions depends on the characteristics of the flow approaching the structure and the geometry of hydraulic boundaries in the immediate vicinity of the structure.
What are the applications of vertical turbine pumps?
Vertical turbine pumps are a type of rotodynamic pump that use radial or modified radial flow impellers in a vertical configuration. Vertical turbine pumps are typically multistage pumps with several levels of impellers encased in a bowl assembly. Vertical turbine pumps can further be classified as deep well turbine pumps, barrel or can pumps, and short set pumps.
A deep well turbine is usually installed in a drilled well with the first stage impeller laying below the water level of the pump. These pumps are self-priming, typically a multistage assembly, and are primarily used to transport water. The multistage
assembly of a deep well turbine pump can be seen in Figure 1 (below). Transporting water from deep wells to the surface is the primary application of these pumps. These pumps transport water to treatment plants, irrigation sprinklers, and to the faucets in our homes. Short set pumps operate very similarly to deep well pumps. Short set pumps will often operate in water pits and typically have a maximum length of 40 ft.
Barrel or can pumps are pumps that are mounted to enclosed containers such as barrels, cans, etc. These pumps operate as booster pumps and are used in situations where inadequate suction is present. These pumps have a similar assembly to the other vertical turbine pumps using a multistage bowl assembly. Additional Net Positive Suction Head (NPSH) is created by these pumps by extending their shaft further into the fluid increasing suction head.
Another unique application of vertical turbine pumps is that the pumps can be run in reverse and be used as hydraulic turbines to generate power. When used in this application the suction nozzle becomes the outlet of the turbine and the discharge nozzle becomes the inlet of the turbine. The efficiency of the pump as a turbine is also comparable to the efficiency of the pump.
Booster Pumps
Sir, in an industry the cooling liquid is fed by a pump to the finishing machine for fine tuning the finished moulds. The cooling liquid contains zirconia, alumina, silica, soda, the centrifugal pump self priming type wetted parts in cast iron is used which gets eroded quickly, and client been trying alternate of aodd type with body in aluminium which also gets eroded and invites constant spares replacement in dedicating manpower exclusively for the work. Theoccurance leads to downtime, and financially consumes a part of the maintenance allotment.is peristaltic pump is suitable ?, kindly request for yours suggestion and the moc suitable M.Mahendran, Gobichettipalayam, Erode dt., TN
Question relates to handling of cutting fluid with abrasive particles. OEM of such machines, usually selects a pump based on the suitability for the duty.
Replacing a centrifugal pump with a PC pump may sound like a good idea when one reads what a PC pump can do. It will be like a panacea to a customer riddled with recurring parts replacement in a centrifugal pump! Fine ground particles of Zirconia and other abrasives have higher density that the carrier fluid. These particles settle down unless they move a velocity higher than settling velocity. The latter depends on SG of solids, size of the particle, viscosity and density of the carrier fluid.
Usually, solid particles are separated by using a hydrocyclone, remaining fluid passes through a filter pressure before the clean cutting fluid is sent to a grinder post.
Appropriate metallurgy for the key components like casing, impeller and shaft wear sleeve is the key to optimum performance. High Chrome steel, Nihard cast iron, high manganese steel parts are often employed. Pumps must be specifically designed for abrasive duty.
Study the literature of manufactures like Schlamenbeger, Wilfley, GIW (now KSB), Metso and others for such applications.
PC pumps are used when the flow rates and operating speeds permit their usage.
Slow speed generally means reduced wear but in a PC pump this is not always true.
At lower rotor speeds, solids tend to settle down in the stator cavity. Constant rubbing of rotor on these settled particles causes a rapid wear on rotor surfacce while stator will show almost no wear at the 6 O’ clock position!
Replacing a centrifugal pump with a PC pump is not always a good idea. Past issues of Pump India carried articles on slurry handling. If possible, go through them again. For specific recommendations, share the duty conditions, pump used, speed of operation, life of components to see if it is worth considering a PC pump as a replacement.
Waste water/ SewagePumps
What is the estimated time between repairs for common wastewater pumps?
The optimal performance or life of pumping equipment will be achieved when the equipment is correctly designed, sized and selected for a given application and the units are operated (and maintained) at the specified conditions.
The design life can be different for varying services and equipment types. In any application, different shareholders in the overall outcome will influence the type of equipment selected and the way it is applied and maintained. Main shareholders and influencers in the design, selection, application and maintenance of the equipment include the following:
Project engineers: minimize capital expenditures
Maintenance engineers: minimize repair hours
Shareholders/owners/GM: maximize dividends and/or share price
Production personnel: maximize uptime hours
Reliability engineers: maximize equipment reliability to avoid failures
▸ Accounting staff: maximize project net present value
In order to obtain maximum reliability and mean time between repairs (MTBR), pump equipment must be properly designed and selected for the intended application, and it must be operated according to the manufacturer’s recommendations. Actual equipment life may not match the predicted value, which depends on the different ways of measuring and analyzing reliability.
Comon pump types for wastewater processes are vertical sump pumps or submersible pumps. In a controlled process, the estimated or mean time between repairs is typically two to eight years, depending on the severity of service for both types of pumps. For pumps that require pressures up to 285 pounds per square inch gauge (psig) and temperatures up to 450 F and are exposed to a harsh abrasive environment, the estimated or mean time between repairs is typically two to four years. If in practice the equipment life falls short of the industry averages, then a thorough review should be conducted.
How is cleaning conducted for wastewater and storm water wet wells?
Organic solids accumulations in wet wells will become septic, causing odors, increasing corrosion, and releasing hazardous gasses. The design of a solids-bearing wet well must both provide for proper approach flow to the pumps, and prevent the accumulation of sediments and surface scum in the sump. The main principle is to minimize horizontal surfaces in the wet well anywhere but directly within the influence of the pump inlets, thereby directing all solids to a location where they may be removed by the pumping oquipment. Vertical or steeply sloped sides are provided for the transition from upstream conduits or channels to pump inlets
Trench-type wet wells are designed to provide for cleaning with the periodic operation of the pumping equipment using a special procedure. The standard ANSI/HI 9.8 Rotodynamic Pumps for Pump Intake Design provides guidance on the geometry necessary to induce scouring velocities during the cleaning procedure. Experience has shown that trench-type wet wells with an ogee transition between the entrance conduit and the trench floor provides optimum geometry for efficient cleaning operations.
Trench-type wet wells for solids-bearing liquids em be quickly cleaned by choosing a time when the inflow is about half of the capseily of the last purtmp. If that pump, operating at full speed, takes more than about a minute to lower the liquid level to the mickle of the trench, two pumps can be activated. The liquid flowing down the ramp reaches supercritical velocity and forms a hydraulic jump that, taking all solids with it. moves to the last pump. The hydraulic jump should move from the toe of the ramp to the last pump in no more than 30 seconds, because operation at low intake submergence is severe service for the pump. As the hydraulic jump passes under each upstream pump inlet, the pump loses prime and should be stopped, and will need to be re-primed prior to the next start.
What pump selection considerations are needed to handle wastewater?
The type of material in the fluid needs to be considered when selecting a proper pump for wastewater treatment. Fluid streams within a wastewater treatment plant are characterized by their properties, as follows:
Large solids
Gint
Sludge
Scum
Flocculated materials The wastewater fluid stream may contain one or more of these characteristics. These properties will create different. considerations that need to be addressed when selecting a pump for the intended service; therefore, the user should identify and communicate to the pump manufacturer the nature of the fluid for each specific application.
Generally wastewater pumps are required to handle solids.
Rotodynamic pumps that are specifically designed to deal with solids and minimize clogging are referred to as solids-handling pumps. Solids may include household and commercial solids, large solids, stringy material (such as rags and hair), sanitary waste, plastic scraps, food waste, sticks, leaves, abrasive materials (such as sand, grit, stones, and pieces of metal), and other inorganic and organic solids. Solid materials that have recently become more prevalent in wastewater flows are: personal wipes, towels, cleaning cloths, and household cleaning materials that are marketed to be discarded through the sewer system. These materials, in addition to the stringy materials and rags, can bind together to create a large mass that can lead to clogging issues in the pump and associated piping.
Grit pump applications require that the pump materials and pump speed to be selected to resist abrasion from grit. To limit the effect of grit on downstream equipment, grit-removal equipment is normally installed at the head of the plant.
Sludge pumping applications can contain stringy material, grit, and grease, and may be viscous in consistency. Some sludge can also contain a significant volume of entrained gases, such as hydrogen sulfide, due to organic bacterial action. The pumps need to be able to address these characteristics and minimize the potential for clogging and gas binding.
Scum is commonly present in storm water pumping and similar applications. Scum consists of all of the floatable materials that are skimmed off the surface of primary and secondary clarifiers. This can consist of any materials that are light enough to float on the water surface. Scum normally consists of oils, grease, fats, wax, soaps, food wastes, hair, and light plastic materials. The scum is removed from the clarifiers and sent to the digester or dewatering system.
Finally Pumps need to be able to handle Flocculated materials.
Pumps that transfer flocculated materials (smaller particles that have agglomerated into larger particles) need to keep the material in the flocculated state and not shear it. Flocculated materials are normally associated with clarifiers where the lighter solids have been flocculated to aid in their removal from the process.
(Courtesy- Hydraulic Institute)
How is cleaning conducted for wastewater and storm water wet wells?
Organic solids accumulations in wet wells will become septic, causing odors, increasing corrosion, and releasing hazardous gasses. The design of a solids-bearing wet well must both provide for proper approach flow to the pumps, and prevent the accumulation of sediments and surface scum in the sump. The main principle is to minimize horizontal surfaces in the wet well anywhere but directly within the influence of the pump inlets, thereby directing all solids to a location where they may be removed by the pumping oquipment. Vertical or steeply sloped sides are provided for the transition from upstream conduits or channels to pump inlets
Trench-type wet wells are designed to provide for cleaning with the periodic operation of the pumping equipment using a special procedure. The standard ANSI/HI 9.8 Rotodynamic Pumps for Pump Intake Design provides guidance on the geometry necessary to induce scouring velocities during the cleaning procedure. Experience has shown that trench-type wet wells with an ogee transition between the entrance conduit and the trench floor provides optimum geometry for efficient cleaning operations.
Trench-type wet wells for solids-bearing liquids em be quickly cleaned by choosing a time when the inflow is about half of the capseily of the last purtmp. If that pump, operating at full speed, takes more than about a minute to lower the liquid level to the mickle of the trench, two pumps can be activated. The liquid flowing down the ramp reaches supercritical velocity and forms a hydraulic jump that, taking all solids with it. moves to the last pump. The hydraulic jump should move from the toe of the ramp to the last pump in no more than 30 seconds, because operation at low intake submergence is severe service for the pump. As the hydraulic jump passes under each upstream pump inlet, the pump loses prime and should be stopped, and will need to be re-primed prior to the next start.
Metering / dosing pumps
What procedures should be followed to ensure proper testing of controlled-volume metering pumps?
Uniform procedures for the setup and testing of controlled-volume metering pumps and for recording the test result data are available in ANSI/HI 7.6 Controlled-Volume Metering Pumps for Test.
The test procedures cover the following:
▸ functional testing of production units
▸mechanical integrity test at rated speed and specified pressure
▸rate of flow and mechanical integrity at rated speed and specified pressure
▸verification of performance to the manufacturer’s specifications
Optional testing for consideration (based on specific application or criticality of service) includes:
▸steady-state accuracy
▸linearity
▸repeatability
▸ net positive suction head or net positive inlet pressure
The items the pump test may use include, but are not limited to, the following:
▸Factory or purchaser furnished driver
▸Drive motor of proper voltage or appropriate design to operate metering pump
▸Safety relief valve to protect the pump from overpressure
▸Closed tank or open sump, properly sized for the pump being tested
▸A discharge pressure gauge suitable for measuring not more than two times the complete range of pressures being tested, located as close as possible
downstream of or near the pulsation dampener
▸If required, dampening devices, such as pulsation dampeners, needle valves or capillary tubes may be used to dampen out the pressure pulsations at the discharge pressure gauge.
For variable speed applications, a means for measuring input speed to the pump should be provided and should be suitable for measuring the complete range of speed over the turndown range.
▸A means for measuring pump rate of flow in liters/hour (gallons/hour), or other agreed-upon units
Test setups that do not conform with respect to intake structure, piping and measuring equipment may not duplicate test facility results.
How are chemical metering pumps used in combined-cycle power plant applications?
Numerous applications in a combined-cycle power plant require the delivery of precisely metered quantities of chemicals. Chemical metering pumps are positive-displacement types and are designed for continuous operation.
One of the key applications is to deliver chemical solutions to control the amount of emissions. Natural-gas fired, combined-cycle power plants produce approximately one half of the CO² emissions and one third of the nitrogen oxides (NOx) produced by conventional power plants. They also eliminate sulfur dioxide emissions.
The combustion turbines in a combined-cycle plant produce low NOx and CO2 emissions. The heat recovery steam generator then uses a selective catalytic reduction scrubber system to reduce the NOx to a very low level (approximately 30 percent of a simple-cycle combustion turbine’s NOx emission using similar technology). Some are as low as 10 percent of the simple-cycle emissions.
The scrubber system is engineered to treat a specific cubic feet per minute range of gas, within a specific temperature range. Further, the system is engineered to reduce the level of contaminants from a specific inlet concentration to a specific outlet concentration. Other typical metering pump applications include boiler feed, cooling tower feed, wastewater treatment, condensate treatment and feeding the makeup water system.
How are chemical metering pumps used in combined-cycle power plant applications?
Numerous applications in a combined-cycle power plant require the delivery of precisely metered quantities of chemicals. Chemical metering pumps are positive-displacement types (see Figure 6.16) and are designed for continuous operation.
One of the key applications is to deliver chemical solutions to control the amount of emissions. Natural-gas fired, combined-cycle power plants produce approximately one half of the CO2 emissions and one third of the nitrogen oxides (NOx) produced by conventional power plants. They also eliminate sulfur dioxide emissions.
The combustion turbines in a combined-cycle plant produce low NOx and CO2 emissions. The heat recovery steam generator then uses a selective catalytic reduction scrubber system to reduce the NOx to a very low level (approximately 30 percent of a simple-cycle combustion turbine’s NOx emission using similar technology). Some are as low as 10 percent of the simple-cycle emissions.
The scrubber system is engineered to treat a specific cubic feet per minute range of gas, within a specific temperature range. Further, the system is engineered to reduce the level of contaminants from a specific inlet concentration to a specific outlet concentration. Other typical metering pump applications include boiler feed, cooling tower feed, wastewater treatment, condensate treatment and feeding the makeup water system.
based on D
D= Outside diameter of bell or pipe inlet
g-Gravitational acceleration
The minimum submergence with units consistent with the outside diameter of the bell or pipe inlet can be calculated using the formula:
S=D(1+2.3FD)
There is some variation in bell velocity among pump types and manufacturers. However, variations in bell inlet velocity are secondary in maintaining acceleration of flow and converging streamlines into the pump bell.
The effectiveness of the recommended pump bay dimensions depends on the characteristics of the flow approaching the structure and the geometry of hydraulic boundaries in the immediate vicinity of the structure.
Multistage pumps
Variable Frequency Drive for Boiler feed Pump? Is it feasible to install a Variable Speed Drive for Boiler Feed Pump? What should be the control for operator while installing VFD for boiler feed pumps?
Is it feasible to install a Variable Speed Drive for Boiler Feed Pump? What should be the control for operator while installing VFD for boiler feed pumps?
N Murali DCM Shriram Consolidated Limited, New Delhi
VFD is a variable frequency drive, which helps to modulate the frequency of the electric power supply to the motor driving the pump. Variation of frequency changes the speed of the motor, because the synchronous speed of an electric motor is governed by the formula 120*f/p where f frequency of supply and p number of poles. So, for a 2-pole motor with 50 supply, the synchronous speed becomes 3000 rpm. An induction motor will have slip, making the actual speed being less than synchronous. For example, a motor with 3.33% slip the actual speed will be 96.67% of the synchronous speed, i.e. 2900 rpm.
VFD can hence help to modulate the speed of any motor, irrespective of the equipment being driven. But changing the speed of the driver i.e. the motor would cause a change in the characteristics of the driven equipment like a pump. So use of VFD has to take into account what change in the characteristics of the driven equipment would be useful and/or acceptable.
VFD can both increase and decrease the speed. Increasing the speed by using VFD can prove hazardous for an equipment like Boiler Feed Pump, because at higher speed the power input required by the pump would be higher. If VFD would increase the speed of the motor, it does not enhance the power rating of the motor. But increase in power input required by the pump when its speed would be higher due to VFD may overload the motor.
On the other hand reducing the speed of the motor would reduce the head and discharge characteristics of pump. If reduction in head of a boiler feed pump would not be adequate to put the pumped water into the boiler, the purpose of the pump would itself be defeated.
What are the benefits of multistage pumps?
Multistage pumps use multiple impellers plus diffusing element stages for developing higher head through the series addition of head from one stage to the next. Types of multistage pumps include the between bearing types, which consist of the axially split BB3 and the radially split BB4 and BB5. These pumps are typically used in applications for boiler feed, reverse osmosis, and other high pressure and temperature applications. Overhung impeller multistage pumps such as the OH7j, the OHlj and the OH13j are useful in low-flow, high-pressure applications and control hydraulic radial load through the use of diffusers.
For multistage pumps, a low NPSH required (NPSHr) first stage can be added to supply the second stage. This is especially applicable when the second stage has a higher NPSHr than the first stage. Vertical and horizontal multistage pumps behave similarly to multiple single-stage pumps operating in series. This should be considered when designing a pumping system that has higher head requirements.
Multistage pumps may also be useful for noise reduction. For pumps of the same power, an increase in the number of stages lowers noise levels compared to a single stage.