Pump Handbook, Fourth Edition. by: Igor J. Karassik, Joseph P. Messina, Paul Cooper, Charles C. Heald. Abstract: The classic pump handbook updated. Pump. Handbook. EDITED BY. Igor J. Karassik. Joseph P. Messina. Paul Cooper. Charles C. Heald. THIRD EDITION. McGRAW-HILL. New York San Francisco. PUMP USERS HANDBOOK 4th Edition This Page Intentionally Left Blank PUMP USERS HANDBOOK 4th EditionR. Rayner ISB.
|Language:||English, Portuguese, German|
|ePub File Size:||20.58 MB|
|PDF File Size:||9.32 MB|
|Distribution:||Free* [*Registration needed]|
MCGRAW HILL PUMP HANDBOOK 4TH EDITION PDF. Save As PDF Ebook mcgraw hill pump handbook 4th edition today. And You can Read Online mcgraw. you to see guide pump handbook 4th edition as you such as. By searching the 4th edition as PDF for free at The Biggest ebook library in the world. MCGRAW. mcgraw hill pump handbook 4th edition | Get Read & Download Ebook mcgraw hill pump handbook. 4th edition as PDF for free at The Biggest ebook library in.
Fire Pumps Chemical Process Pumps Food, Beverage and Pharmaceutical Pumps Petroleum Production, Pipeline and Product Pumps P u l p and Paper Pumps Solids and Slurry Pumps Trade Names Index Advertisers' Names, Addresses and Contact Numbers Editorial Index Advertisers Index This chapter covers those principles that are independent of the type of pump and essential to a thorough understanding of the criteria that govern the performance of flow systems.
They will be referenced throughout the text. The reader is encouraged to refer to them freely unless there is a full understanding of their meaning and use. Definitions: Fluid: A liquid that may contain or be mixed with solids, vapours, or gases. Liquid: A pure fluid that contains no solids, vapours or gases. Mass: M , kgm Ibm is a measure of the amount of matter in an object. It may be considered as that property of an object by which it exhibits inertia. An international standard prototype mass exists and all mass measurements can be done on an equal arm balance, traceable to that prototype.
Weight: W , kg lbf is a measure of the gravitational pull on a body. Karassik held senior positions at the Worthington Pump and Machinery Corporation.
Paul Cooper served as director of research and development for Ingersoll-Rand Research. Charles Heald is former chief engineer and manager of engineering with Ingersoll-Dresser Pump Company. Joseph P. Messina also one of the original editors, has spent his entire career in the pump industry, and his past contributions on pump and systems engineering continue to be presented in their entirety in this edition. He assisted in updating the Hydraulic Institute Standards and taught centrifugal pump courses.
He has been a contributor to the technical journals and holds pump-related patents.
It has proven satisfactory in the bulk of cases on catalogue type pumps of low to medium specific speed. In the case of large boiler feed and large irrigation pumps and any of the high energy engineered type pumps the NPSHR criterion might better be lowered.
The effect of this cavitation on pump damage is non-existent on some pumps whereas on others it can be profound. Hydraulic designers are slowly gaining more insight into this area. They can control the length of the bubble to avoid cavitation damage with their blade design and then test with a strobe to measure the bubble size and confirm their calculations. See chapter on testing. Much more expense and capital costs, in terms of sophisticated instrumentation, are involved in tests when a lower pressure drop criterion is required.
Cavitation inception is most likely going to start when some localized pressure drops to a point that vaporization takes place. This may be much sooner than would be justified by looking at the mean or average flow conditions. Suction piping is a major consideration, especially if it results in asymmetrical flow conditions entering the pump.
Refer to the section on suction piping later on in this chapter. The BEP point is the design point of the complete pump. He points out that "It is inherent in the dynamics of the pressure field that every impeller design must recirculate at some point-it cannot be avoided". He further states that discharge recirculation can be reduced in design but, only with an accompanying reduction in the rated efficiency of the pump; suction recirculation could likewise be reduced with an accompanying increase in NPSHR and that optimization of efficiency requires a reduction in the safety margin between the rated capacity and the discharge recirculation capacity.
Since that time these points of incipiency have been found to be conservative on many pumps, especially so on the catalogue types. In addition designers of engineered type pumps have found ways to significantly lower these incipiency points and still maintain good pump efficiency.
The result has been recommendations not to exceed certain suction specific speeds. These recommendations while appropriate for the particular pumps and existing conditions in the respective surveys, have been inappropriately used on a more universal basis.
As defined suction specific speed is an appropriate index for impellers of the geometrically similar inlets. Moreover, the units in these surveys were high energy units, used in refineries and utilities respectively. Other applications are not be as severe.
The Hydraulic Institute set up a pilot survey on double suction, horizontal split case catalogue pumps of low to moderate energy because experience of its members on catalog pumps seemed to be in the order of magnitude of less than 1 suction recirculation failure in , whereas on engineered pumps in the two surveys reported the failure rate was of the order of magnitude of 1 in Pumps with suction specific speeds up to 15, ran without cavitation failure except for the 13 mentioned above.
There are those who believe that Suction Specific Speed, S should have been defined at the shockless flow capacity of the impeller rather than the bep of the pump which includes the performance of the easing, wear ring leakage. Suffice it to say here that S alone is not a sufficient basis to determine the limits of pump operation. If it is to be used, then its own limitations must be recognized. There is a connection between discharge and suction recirculation when the vane overlap is low.
Discharge and suction recirculation can combine and both start at the discharge incipiency point. The Pump manufacturers minimum capacity limitation is the limiting flow that a pump manufacturer will show on his curves and documentation based on experience as to a safe minimum flow limit based on failures or in some cases vibration limit.
Cavitation surge: Surging at the inlet is associated with low flows and reduced NPSH. A large spinning cavity in the inlet pipe grows and collapses. This is a high amplitude, low frequency phenomena in the Hz range with accompanying cavitation. One blade will stall then the next and so on.
Centrifugal Pump Handbook
Minimum allowable flow due to temperature rise occurs in the recirculation mode when the heat added to the fluid being pumped due to pump losses is greater than the amount of heat being carried away.
Temperature rise, AT can be calculated from the total head and efficiency as follows: Plot the Temperature rise. H and 11 are obtained from the characteristic curve for various capacities. One can see in Fig 5. However this pump is a relatively low head pump.
Look at another one with about twice the head and lower part load efficiencies and see what the effect is. Example 2 Redo based on the pump whose characteristics are shown in Fig 5. The results are plotted in Fig. One can see that the higher head lower specific speed and lower efficiency unit is more sensitive to temperature rise at low flows, with the increase starting to accelerate as the flow dropped below 40 gpm.
This is also an appropriate time to point out that this temperature rise can have an adverse affect on NPSHA. This is especially true on units with specific speed of 19 or less, and this could cause localized flashing. Other low flow considerations Power characteristic curves on high specific speed units rise with reduction in flow. Therefore care must be taken on such units that the motor is not overloaded.
When the pumpage has entrained air, the ability of the pump to handle it is reduced at lower flows, and the result could be a choking condition alternate pumping and no pumping. P a r a l l e l - Series O p e r a t i o n Parallel - Series Operation are common requirements but each has certain considerations that must not be overlooked.
Parallel operation of two or more pumps requires consideration of adequate inlet piping sizing and take-off design See Chapter on Sumps and Inlets, as well as adequate steepness of the characteristic curves for stability. The steepness of the curves and the magnitude of the static head component are two of the major variables. Generally, pumps on systems that have high static head components would give better performance in parallel.
System curves made up by a high percentage of friction losses will show higher flows through two pumps in series than two in parallel. Parallel curves. However, series operation where parallel operation would meet the head requirements means giving up the benefits of having one or two pumps on depending on the load requirements. In series both pumps must be left on unless the head drops to less than half of the rated head. Series and parallel curves for two identical A units and then two identical B units are superimposed on each, illustrating some of the points that have been made.
Had the power curves been given, the question of which pump combination was expected to draw the most power could have been resolved. Add the heads of each pump at different capacities to obtain the parallel operation curve and the capacities at different heads to obtain the series operation curve. It is not necessary to stick with identical pumps for series and parallel operation.
In the first case, the second pump in series should have approximately the same capacity as the first, but could have a different head. In the case of parallel operation it is desirable that the second pump has approximately the same head as the first, but the capacity could be different. Intake Design: Sumps, Tanks and Suction Piping The main source of hydraulic problems in pumps arises from improper design of the suction side of the system or intake.
The function of an intake design is to supply an evenly distributed, non-rotating flow, free of entrained air and foreign- material with adequate submergence to the pump impeller. Definitions Intake: The structures into which liquid to be pumped is directed. A wetted chamber with a free surface which receives liquid to be pumped and from which it is pumped. Wet Pit, Wet Well: A sump having its bottom below the bottom elevation of its inlet, ground level or some other reference elevation.
Dry Pit: A non-wetted chamber housing pumping equipment located adjacent to a wetpit. A rotation of a portion of the fluid. In the case of sumps and tanks the leading statement in this intake design section means that their inlet should be below the minimum liquid level to avoid entraining air and as reasonably far away from the pump as possible to keep the flow as uniform as possible.
Inlets with free-falling discharge to the sump or tank liquid level should be avoided as they cause entrapped air bubbles which can affect pump performance. The influent should not impinge against the pump, jet directly into the pump inlet or enter the sump or tank in such a way as to cause rotation of the liquid in the containment area.
The latter depending on the motor winding's temperature limitations and ability to dissipate the energy absorbed in the form of heat from the starting acceleration period during the running and shut down periods between startups and still leave the minimum liquid level at the end of the run period. Once the volume of a sump or tank is ascertained, the next criterion is the dimensions.
The Hydraulic Institute 17has set up e. In the case of a single pump, the dimension S, a minimum dimension determines the width. Ideally, the dimension would be as deep as possible, but economics is the deciding factor. An average dimension is dependent on the type of pump. The pump manufacturers recommendations should be sought here.
The edge of the suction bell should be close to the back wall. In those cases where this may not otherwise be possible a false wall should be installed. The shape and additions to sumps for multiple pumps are complicated. If at all possible the design should not have water flowing past one pump to get to the next unless certain criteria are me Note that sumps for solids bearing processes require some special considerations. The sump velocities, for example must be higher to keep the solids in suspension.
The sidewalls should be shaped to avoid solids settling in the corners. Model Tests If the sump design is not a relatively simple one that can clearly meet the guidelines shown here and in the attached references, it may be necessary to conduct a sump model test to assure adequate design.
Tanks including process vessels It is common to take the suction line off the bottom or side of a process or suction tank. General rules for sound intake design apply to suction tanks. In particular adequate submergence must be provided to prevent vortexing. One foot of submergence for each foot per second of velocity at the suction pipe inlet is recommended.
A maximum velocity of 6 fps is suggested. Bellmouth or rounded inlets are recommended. If the recommended submergence cannot be obtained, the inlet pipe diameter should be increased or vortex breakers installed.
Recommended breaker designs are shown in Fig. Baffles should be placed between the inlet and outlet connections to prevent short circuiting. Suction Piping The function of good suction piping design is to provide uniform, non-rotating flow to the impeller avoiding air entrainment with a minimum of friction loss. In general, all piping should slope upward to the pump. On double suction pumps the elbows should only be installed in a plane perpendicular to the pump shaft and concentric reducers should be avoided in favour of eccentric reducers with the horizontal side on top.
Long radius elbows and a larger pipe diameter than the pump suction with a reducer are recommended ways of increasing the NPSHA. Care must be taken with flange gaskets so as to avoid any protrusions into the suction pipe. This has resulted in problems of catastrophic proportion in numerous cases, especially in low NPSHR situations and flanges near or at the suction of the pump. S and Robert, R. Bailey, Editor, Copyright Sweeney and G.
Pump does not deliver liquid. Impeller rotating in wrong direction. Pump not properly primed - air or vapour lock in suction line. Reverse direction of rotation. Stop pump and reprime. Inlet of suction pipe insufficiently submerged. Air leaks in suction line or gland arrangement. Pump not up to rated speed. Ensureadequate supply of liquid. Makegood any leaks or repack gland. Increase speed. Air or vapour lock in suction line. Foot valve or suction strainer choked.
Restriction in delivery pipework or pipework incorrect, Makegood any leaks or repack gland. Clean foot valve or strainer. Clear obstruction or rectify error in pipework. Pump does not deliver rated quantity. Head underestimated. Check head losses in delivery pipes, bends and valves, reduce losses as required. Unobserved leak in delivery. Examine pipework and repair leak.
Blockage in impeller or casing. Remove half casing and clear obstruction. Excessive wear at neck rings or wearing plates. Dismantle pump and restore clearances to original dimensions. Impeller damaged. Dismantle pumpand renew impeller. Pump gaskets leaking. Renew direction of rotation. Pump does not generate its rated delivery pressure Impeller rotating in wrong direction.
Impeller neck rings worn excessively. Dismantle pump and renew impeller or clear blockage. Renew defective gaskets. Impeller damaged or choked. Pump loses liquid after starting. Suction line not full primed - air or vapour lock in suction line. Ensureadequate supply of liquid at suction pipe inlet.
Make good leaks or renew gland packing. Clean out liquid seal supply. Liquid seal to gland arrangement logging ring if fitted choked. Logging ring not properly located. Unpack gland and relocate logging ring under supply orifice. Serious leak in delivery line, pump delivering more than its rated quantity.
Excessive vibration Renew defective gaskets. Repair leak. Reduce speed.
Gland packing too tight. Stop pump, close delivery valve to relieve internal pressure on packing, slacken back the gland nuts and retighten to finger tightness.
Karassik I.J., Messina J.P., Cooper P., Heald C.C. (ed.). Pump handbook
Mechanical tightness at pump internal components. Pipework exerting strain on pump. Dismantle pump and renew impeller. Dismantle pump, check internal clearances and adjust as necessary. Air or vapour lock in suction. Pump and driving unit incorrectly aligned. Worn or loose bearings. Impeller choked or damaged. Dismantle pump and straighten or renew shaft.
Remove pump, strengthen the foundation and reinstall pump. Foundation not rigid. Bearing overheating Action Ensureadequate supply of liquid at suction pipe inlet. Coupling damaged. Renew coupling. Disconnect pipework and realign to pump. Pump and driving unit out of alignment. Disconnect coupling and realign pump and driving unit. Replenish with correct grade of oil or drain down to correct level. Oil level too low or too high. Wrong grade of oil. Dirt in bearings. Moisture in oil.
Bearings too tight. Drain out bearing, flush through bearings; refill with correct grade of oil. Dismantle, clean out and flush through bearings; refill with correct grade of oil. Drain out bearing, flush through with correct grade of oil. Determine cause of contamination and rectify.
Ensure that bearings are correctly bedded to their journals with the correct amount of oil clearance. Renew bearings if necessary. Probable Cause. Bearings wear. Too much grease in bearing. Clean out old grease and repack with correct grade and amount of grease. Dismantle pump, straighten or renew shaft. Rotating element shaft bent. Ensure that only clean oil is used to lubricate bearings.
Refill with clean oil. Lack of lubrication. Ensure that oil is maintained at its correct level or that oil system is functioning correctly. Bearing badly installed. Ensure that pipework is correctly aligned to pump. Irregular delivery Excessive vibration Refer to excessive vibration symptom. Fault in driving unit. Examine driving unit and make good any defects.
Make good any leaks and repack gland. Excessive noise level Inlet of suction pipe insufficiently immersed in liquid. Ensure adequate supply of liquid at suction pipe inlet. Make good any leaks or repack gland.
Dismantle and renew bearings. Remove pump and driving unit, strengthen foundation. Figure 2. The end suction configuration is shown in Figs. Its suction and discharge nozzles are perpendicular to each other, with the flow in the suction being along the centreline of the shaft for some distance. There is generally no shaft extension into the incoming flow. The in-line pump configurations see Europump Terminology or Hydraulic Institute Standards have radial inlets as opposed to the end suction inlet.
Radial inlet means the flow comes into the pump inlet perpendicularly and has to make a fight angle turn coincident with the shaft before it enters the impeller. The between bearing unit configuration is the counterpart to the overhung configuration.
Figs 6. A submersible pump is one whose driver is submerged along with the pump.. A close coupled pump is one which has the impeller mounted on the motor shaft, as opposed to a separately coupled unit that has its own shaft separate from the motor' s and connected with a rigid or flexible coupling. Some pumps have centreline support. This configuration is used where large temperature changes are expected and special provisions are required to maintain alignment.
These large temperature swings do not necessarily have to be in the process fluid itself, but could be in the difference between shutdown and operating conditions with a high temperature process fluid. Refinery processes are a good example of this.
Some pumps have special features that give them a special designation, irrespective of application: The liquid entrains air within the impeller. The air-free liquid returns to the impeller through the bypass opening for reentrainment.
The air re-entrainment and removal cycle continues to reduce the pressure in the suction line. The liquid rises in the suction pipe until the pipe is flooded. The pump then functions much like any end suction centrifugal pump.
Once primed, the increased pressure in the volute reverses the flow through the bypass opening. Even the regenerative turbine pump requires enough liquid to form a seal between the suction and discharge sections. Some types have an internal trap on the suction side that can be provided on an optional basis to perform this function.
None of these pumps, however, can perform the function of a vacuum pump and expel enough air to let the water be drawn into the impeller. Adaptations are made internally to the pump or externally to purge the air out of the suction side. A pump using external means such as a vacuum pump is not considered a self-primer. If internally provided eductors are used or the pump is shaped to perform the air removal the pump is considered to be self-priming. With the exception of the regenerative turbine this is accomplished by entrapment of air in the impeller or at its exit, the separation of this air in the stilling chamber requiring a large free surface and the return of the air free liquid to the exit of the impeller or the impeller itself where the cycle repeats itself until enough air is removed from the suction to allow normal pumping.
In the process, the liquid is continually being recirculated in the discharge of the pump. Suction and discharge recirculation have been used in the past, but today' s pumps rely on discharge recirculation and no liquid is returned to the suction. In all of these cases some residual liquid must exist in the pump for the priming cycle to be effective, but designs generally hold enough liquid after the first charge that additional charges are not necessary under normal operating conditions.
Vortex pumps Also called torque pumps are pumps with recessed impellers see Figs 5. They are able to handle relatively large amounts of entrained gas and solids and stringy materials. The severity of the abrasiveness of the solids that can be handled is a function of the ruggedness of the design, the materials and the use of sacrificial wear plates. They are found in use in waste water, mining, pulp and paper, chemical, food, industrial and agricultural applications. Vertical radially split bowl, turbine, pumps Also called bore hole and diffuser pumps, were originally developed for deep well applications.
The depth of the water in the well was accommodated by lowering the pump into the well until the suction was adequately covered by water.
The head was determined by the depth of this first stage, the losses pumping the water to the ground level and any FIGURE 6. Enough pairs of impellers and bowls stages were then added to meet the head requirements and a segmented shaft connected the rotating assembly with the driver at ground level.
A segmented column pipe carried its weight along with that of the bowls, inlet bell or suction pipe and strainer, line bearings etc. The limit in depth is determined by the maximum allowable elongation of the column relative to its original length, due to its weight and the down thrust. Below this limit a submersible configuration of deep-well submersible turbine pump is used.
They are also used for pumping from open bodies of water such as ponds, lakes, rivers and oceans, as well as mine dewatering, sumps and caverns, power plants and oil field repressuring. They are especially well suited to low NPSH applications and since the first stage is submerged they are inherently selfpriming. This type ofpump lends itself to a fine tuned solution of a specific application need. Not only can stages be added as required, but hydraulic designs can be selected over the range of specific speeds from 10 to 12 and the maximum efficiency obtained.
As in volute type pumps, the lower specific speed impellers radial are used for the higher heads; the mid-range specific speeds mixed flow for medium heads medium flows and the highest specific speeds, axial-propeller for high flow, low head applications. Their range of speeds is generally below rpm.
An outer casing is applied for discharge pressures above kPa psi. Other advantages of this type of pump are the small footprint at floor or ground level and the ability to customize mechanical and metallurgical design options to the customer' s needs. Disadvantages are submerged bearing system, remoteness that results in neglect 6.
Open and closed impellers are used with the latter preferred. Open impeller wear can result in the need replacement, whereas this is not generally the case with closed impellers. Also, open impellers require setting adjustment, that can be tricky, to optimize efficiency. The barrel or can pump as shown in Fig. This pump with its own sump can be sunk into a floor with minimal relative expense. Vertical turbine pumps are driven by induction or synchronous solid or hollow shaft motors or internal combustion engines through right-angle gear drives.
It is common with variable speed drives to pass through a pump system natural frequency. This need not be a problem as long as provision is made to prevent continuous operation in this area. Submersible pumps Submersible pumps are pumps with connected motors that can be submerged into the sump, pit or well. In some cases the submerged, hermetically sealed motors are filled with oil and in other cases they are filled with air along with separate water cooling of the motor FIGURE 6.
The smaller size pumps are furnished with air cooled motors requiringno coolant flow through the pump motor casing. The larger pumps are cooled with pumpage most frequently, utilizing the impeller back vanes as the pumping means.
Seal chambers filled with oil separate the motor from the pump on some units. A submersible slurry pump with liner is shown in Fig.
These four pumps have a combined flow rate of 78 MGD. Diffuser and volute pumps of many types have been furnished in submersible configurations. Submersible pumps can be portable and are commonly used as contractors pumps for utility cleanup. Further coverage of these pumps is included in Chapters 24 and They need and have no packing or mechanical seals and are sometimes called glandless pumps.
Four Flygt submersible propeller pumps handle the flow at a combined rate of 78 MGD. Centrifugals are the most efficient of the hermetic types. They are available in two basic variations: Magnetic Drive and Canned Motor. The latter has been around since the twenties but has built up most of its usage in the last 40 years. The main difference between the two types is in the way the rotor is driven.
The magmeticdrive rotor, see Figs 6. In the case of the canned-motor pump, the stator with its windings is isolated from the rotor by a sheet metal shell, or can, that is located in the air-gap of the motor. Canned motor unit units have been improved substantially. The hermetic magnetic-drive pump Figs. Today a customer finds that he has a choice of many pump manufacturers to supply his needs in this area.
It can also be said that the seal manufacturers at the same time have had a major development program of their own which has provided a magnitude improvement in seal reliability and reduced leakage rates to a point where zero leakage can be approached with conventional pumps. The seal less designs presently have a first cost of approximately two times that of a conventional pump and their failures can literally destroy the pump, but the new designs have a secondary containment that will avoid any catastrophic leakage for a period of several days.
Condition monitoring equipment can also be furnished so that impending failures can be avoided. In the case of many plants, where the total amount of emission has to be determined and reduced to the limit set by the new regulations, the solution is often a mixed one of retro-fitting some existing pumps with new seals and replacing others with new seal less pumps.
Maintenance capabilities and costs can also be a deciding factor in the user' s decision. The canned pump, see Figs. A main consideration with this pump is the expected life of the liner with a corrosive process fluid once the best material option has been selected.
Advantages and disadvantages of the two are as follows: No heavy bed plate required Thin supports allow unit to move as an entity without creating internal distortation No special foundation requirements No alignment required. Low maintenance Less parts Experience with bearing monitors using power consumption monitors as backup has been excellent.
Secondary does not require a mechanical seal. Lowest failure rate Special motor must be serviced by mfr. Explosion-Proof applications require a testing agency U. Motor heat must be dissipated to prevent flashing of pumpage Whole pump replaced if windings fail Capability for secondary containment Thin can 0. Special instrumentation required to determine rotation. Low tolerance to solids in pumpage due to close clearances between can and rotor or stator.
Maximum viscosity is cp. Limit could be as low as 20 cp. Higher temperature pumpage require isolation and external cooling of the stator cavity to prevent winding failure. Cannot handle high temperatures as easily as magnetic drives. Pumped fluid must provide adequate bearing lubrication.
More tolerance to solids than canned motor pumps. Possibility of misalignment of motor and magnetic-drive shafts Three sets of bearings: Does not contain bearing monitors. Cannot handle the pressures of canned rotor pumps.
Decoupling can be serious Alignment can be tricky and costly. Sealless pumps eliminate leakage across seal faces 6.
One user 8of many canned and magnetic-drive units found that they even had to go back to conventional pumps on one application because they were too overzealous in applying hermetics.
If they are not properly applied and maintained, they will fail, sometimes drastically. Training is something you will have to commit to immediately because these pumps are sensitive to human error and improper operation or maintenance. To decide if a pump is right for your application, you need to understand their design, their weaknesses and be ready to provide the vendor with complete necessary information on design and off design conditions and the properties of the pumpage.
Users point out that reliability is as important a factor as emission elimination, especially with difficult to seal liquids such as those that harden when exposed to air or water. Special designs are called for if the pumpage has poor lubricating qualities common , poor heat absorption, is corrosive, has low vapour pressure or low or high viscosity.
If you have an application where the sealed pumps are failing repeatedly, you must determine if the problem is in the pump or system.
Users have replaced sealed pumps with hermetics only to find that they failed too. Hermetic units generally use the pumpage as a lubricant and coolant to take away motor heat and eddy current losses: In the case of the canned motor pump and magnetic-drives with metallic cans; the eddy current losses and lastly, friction losses in the bearings of both types as well as impeller disc friction losses.
Any system condition that will cause the the pumpage being circulated to boil can result in a failure. Bearing failures and running dry are two of the main causes of failures in hermetic pumps.
Viscosities that are too high even 30 cp could require special considerations for the small clearances and conduits to handle can cause the coolant to boil.
Viscosities that are too low can cause bearing failures due to inadequate hydrodynamic film in the sliding bearings of either type. Suspended solids, fluids that polymerize and cavitation can also result in failures. Most of these failures are caused by misapplication or operator errors. Most users see a reduction in failures as their staff get used to the differences of operating these pumps vs the sealed types they have been used to.If internally provided eductors are used or the pump is shaped to perform the air removal the pump is considered to be self-priming.
H and 11 are obtained from the characteristic curve for various capacities. The single suction impeller can be any of the above except Fig. Regenerative Turbine Pumps Randtke, Ph. Datum is the horizontal plane of a pump which serves as the reference point for Elevation Head measurements.