approach the field of centrifugal pumps, and more experienced people .. QI1Joss~li Pdf are also part of the hydraulic losses, and are induced by the rotational. Grundfos has developed the Pump handbook, which in a simple manner deals with various Characteristics of the centrifugal pump. 'The Centrifugal Pump' is primarily meant as an inter- nal book and is aimed at technicians who work with development and construction of pump components.
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decreased centrifugal pump performance and increased power requirements. Consideration of the pump suction-side line losses need to be calculated. This tutorial is intended for anyone that has an interest in centrifugal pumps. How to verify that your centrifugal pump is providing the rated pressure or head?. Centrifugal Pumps Handbook - Ebook download as PDF File .pdf), Text File .txt) or read book online.
Inlet velocity in suction bell range 1. Guidelines for Inlet Pipelines 99 Figure 4. Guidelines for Inlet Pipelines As already mentioned, flow disturbances in the form of unequal velocity distribution and vortex at the pump inlet are detrimental to pump performance, cavitation behavior and smooth pump running.
Attention should therefore be given to the reasoning and guidelines below for avoiding such troubles. The approach flow pipe should be engineered so that sources of disturbance like bends, branches or valves are as few as possible. Such components may cause uneven velocity distribution and vortex formation. If bends are arranged in short succession, the velocity pattern will be worsened further. Consequently, all influences leading to asymmetrical approach flow must be avoided.
Any bends upstream of the pump inlet nozzle should, if possible, be placed only in the plane of symmetry of the pump. If the approach flow symmetry is disturbed, appropriate precau- tions must be taken to minimize such disturbances. Flow acceleration. In critical cases a flow straightener may be required.
Bends with ribs The data given below are minimum requirements which should be adhered to. The distribution of the flow rate between the two impeller halves is disturbed. Performance is impaired, pressure pulsations may increase and the hydraulic axial forces are no longer balanced.
In general, attention should always by given to the hydraulically proper fitting of valves, especially in suction or inlet pipes. Inlet pipe connection to the suction reservoir Hydraulic disturbances in the operational behavior of pumps see also section 4. This may lead to vortices in the approach flow, and hence disturb the smooth operation of the pump.
Guidelines for Inlet Pipelines Figure 4. The velocity at the branch connection must not exceed about 2. The inlet cross in Fig. It supports the guide plate at the same time.
This inlet cross ought to be provided whenever possible, to prevent vortices and swirl. The inlet pipeline is connected to the feedwater tank via a cone, to keep the inlet velocity as low as possible. The inlet has four axial vanes to prevent vortex formation. The rounding on the inside of the tank is intended to avoid sludge from being drawn into the pump.
Above the inlet cross is a perforated plate, enabling vapor bubbles to be separated in the tank in the event of sudden pressure drop load change. The actual submergence S is not taken into account here but is regarded as an additional safety margin. Water transport and supply systems are often extremely varied in nature, so that it is impossible to find by approximation procedures a solution that will reliably preclude overstressing of components in any system.
In steady operation, the flow velocity is constant in time and space. By contrast, in transient flow, the velocity varies in time and location.
Transient flows occur at every change from an existing steady operating state to a new one. Pressure surges result from transient flows. Consequently the following operation modes in pumping stations are associated with surging problems: With the exceptions of power failure and inexpert operation, all of them are deliberate actions which can be performed properly.
On the other hand, power failures are unintentional and generally constitute the most severe case. Additional safety devices must be provided against power failure in particular. For a sudden change in the flow velocity, Joukowsky found that the maximum pressure change amounts to: From its point of origin the disturbance travels through the pipeline system at the propagation speed.
In the example shown in Fig. Here the disturbance is reflected. The pressure at the time t and the point x in the system is always the sum of all pressure waves that have passed the point x at the time t. Using the example in Fig.
It is assumed that Figure 4. Consequently for this theoretical consideration there is a sudden speed change from the steady-state value c to 0. The pipe friction is taken as zero as well. In the steady state Fig. According to the Joukowsky equation there is a pressure drop of DH: Ahead of the pressure wave the original velocity still prevails, whereas the velocity behind the pressure wave is zero.
Behind the pressure wave the pressure has dropped by DH: In the entire pipe there is now zero velocity and a pressure reduced by DH.
The pressure drop DH cannot maintain itself, consequently there is a pressure rise and a flow velocity c emerges: The entire pipe is now under the original pressure H but the velocity is directed towards the pump. Reflection at the closed end of the pipe now causes a pressure rise. The cycle described above is repeated, though this time with a pressure increase: Pressure Surges in Pipeline Systems Figure 4.
The application limits must be borne in mind, otherwise false conclusions may be drawn. Computer-aided calculation This method yields accurate results for any system in a short time. It is often employed with simple tools, as a complement to approximation. If the calculation is to supply meaningful results, the system data used as inputs must also be defined precisely.
Table 4. If calculations are carried out in the project planning stage, the fol- lowing variables must be known as a minimum: The purpose of every pressure surge investigation is to determine the size of a protective device so that no limits are exceeded anywhere in the plant, even in the most extreme transient case this is usually power failure. The limiting factors are as follows: Minimum pipeline pressure. The pressure in the pipe must not be allowed to drop to an extent that the vapor pressure is reached, other- wise water column separation must be expected, with a subsequent extreme pressure rise.
In many cases it is not permissible for the atmo- spheric pressure to be undershot by more than a few meters if the pipe is not to be crushed by the external pressure. With drinking water pipelines the atmospheric pressure must not, as a rule, be undershot. Otherwise there is a risk of impurities getting into the system.
With plastic pipes, special attention must be given to the admissible external pressure. Type of pump, number, maximum number in parallel operation 2. Maximum flow rate 5. Maximum flywheel admissible for motor mass, J 6. Pipe diameters, material and wall thicknesses Boundary conditions: Maximum pipe pressure admissible Minimum pipe pressure admissible Type and closing law of the valves Maximum pipeline pressure.
The nominal pressure rating of the pipes and the design pressure of the components must not be exceeded. Maximum reverse speed. This is important in pumping installations with controlled valves and also in turbine installations, on account of mechanical stressing of the pump, motor or turbine.
Pipeline profile. In order to correctly assess the extreme pipe pres- sures this must be known exactly. The pressure surge investigation often reveals that a better pipeline profile will allow much smaller protective devices.
However, this advan- tage can be exploited only if the transients have already been examined at the project planning stage. This may be achieved by the following measures. Pressure Surges in Pipeline Systems The speed change is reduced by: A flywheel. This prolongs the pump rundown time. The limits for employing a flywheel are systems up to about 2 km pipeline length. For special versions with separate intermediate flywheel bearings, only the acceleration is of importance. A surge tank installation.
This takes over full pipeline flow surge with virtually no time lag. With a suitable surge tank, the minimum admis- sible pressure is maintained in most systems. Low-pressure systems are frequent exceptions to this. Figures 4. The water level is monitored automatically. If the level in the surge tank exceeds a maximum due to leakage or defective compressor , the installation must be taken out of service till the level can be kept normal again. Reducing the active length of the system. This results in one or more additional boundary conditions reflection points: Surge tank or standpipe.
Both options have the great advantage of being effective even with the smallest pressure wave. Standpipes up to 82 m in height have been built. One-way surge tank. If the use of a standpipe is ruled out, a one-way surge tank is often provided Fig. However, this takes effect only when the pressure in the pipe drops to the level in the tank.
All dis- turbances that have passed the junction up to that time cannot be influenced. Air valves. These too are effective only from the moment when atmo- spheric pressure is reached in the pipe at the point where the valve is fitted. Substantial volumes of air may be drawn into the system; con- sequently air valves are ruled out for water supply systems. Problems may arise in operation if greater quantities of air remain trapped in the system unstable operation, higher pressure losses.
Good venting must therefore be assured. If only the maximum pressure is important, or if it cannot be reduced sufficiently by primary protection measures, the following secondary protective devices may be considered: Pressure relief valve Fig. This must operate with minimum inertia and sufficient damping, otherwise pressure pulsations may be excited. When a certain pressure is exceeded, the valve opens to atmosphere, allowing water to escape from the system through slots in the valve cylinder.
Optimizing the closing law of controlled stop valves. This effects a controlled reduction of reverse flow in the system to zero. Usually a compromise must be found by calculation between pressure surge and reverse speed. Check valve in main pipe. In the event of reverse flow, this divides the pipe system into sections with different maximum pressures. Lower- level pipe sections can then be built for a lower nominal pressure.
The higher the pressure in the system, the shorter the pump rundown time tA i. If the check valve of the pump is still partly open at the time tA, reverse flow begins. This reverse flow causes rapid closing of the check valve. The result is a considerable pressure peak, accompanied by a very loud noise in extreme cases a report. The condition for preventing flap ham- mer is: Flap hammer can be prevented in the following ways: Selection of a check valve with a closing time conforming to the specified tS.
Increasing the mass moment of inertia of the revolving parts with a flywheel, so that the pump rundown time is prolonged. Installing the surge tank at some distance from the pump. Limits to this are set by the building, unless a separate building is provided for the surge tank installation, which must, however, remain within the control range of the pumping station.
Example 1 Figures 4. A total capacity of 1. The minimum pressures are plotted against the pipeline profile in Fig. Without protection and with a flywheel, the flow curve is very steep, causing an extremely steep pressure drop. Only with the surge tank is a slow, steady change of flow rate possible, resulting in a sufficiently flat pressure curve. The necessary surge tank size is 50 m3, with an air volume of 20 m3 under operating conditions. Example 2 This example shows the results of measurements on a system with m pipe length, m geodetic head and 0.
Without additional protection the admissible pipe pressure of m is seriously exceeded Fig. An attempt was made to prevent column separation in the critical part of the pipe by means of air admission valves. As Fig.
Only the provision of a surge tank brought success Fig. At the beginning of the pipe the maximum pipe pressure is now only m. To confirm fulfillment of the guarantee, shutdown tests are to be performed with the data on which the calculation was based, not later than at the conclusion of commissioning. All data of relevance to steady- state operation must be recorded.
During the shutdown test the approach flow pressure, pressure on the discharge side, pump speed and stop valve opening must be recorded with electronic instruments. The basic rule is: Additional devices by no means enhance reliability.
On the contrary, they clutter the instal- lation and increase the number of possible trouble sources. Partial or full automation should be justifiably economical. Minimum attendance and maintenance costs should be aimed at.
Only a small selection of the possible measuring and monitoring instru- ments for protecting centrifugal pumps can be listed here see exam- ples in Fig.
Additional external conditions for assuring pump protection are: Determining the minimum flow rate. Operational reliability is paramount. When choosing instruments the ability of the suppliers to render service on-site must be verified. Noise Emission from Centrifugal Pumps Figure 4.
A clearly defined functional description of the entire pumping unit pump, motor, control system, protective devices and power supply must be available prior to commissioning. For instruments the constraints affecting three-phase motors men- tioned in section 7. As far as the installation allows, whenever possible the pumps should be arranged so that they are always under inlet pressure, i. This makes for simple starting and higher reliability. Depending on the medium, a distinction is drawn between airborne, structure-borne and liquid-borne sound: Sound pressure is the quantity perceived by the human ear.
Sound power is the acoustic power emitted by a sound source. Sound intensity is the sound power per unit area. Structure-borne sound is the sound propagated in a solid medium or at its surface. Vibrations on the surface may radiate airborne sound. The various levels are defined as: Typical sound pressure levels are: Depending on the kind of frequency filter, distinctions are drawn as follows: Its maximum sensitivity is around 4 kHz, falling off steeply towards low frequencies below Hz especially.
In order to adapt sound mea- surements to hearing sensitivity, various frequency weightings for acoustic signals have been introduced. Weighted sound pressure levels A, B or C are then referred to.
Weighting A allows for aural sensitivity to moderate sound pressure levels, weighting B for medium and weighting C for high sound pressure levels.
Weighting curves A, B and C are shown in Fig. Nowadays the A-weighted sound level LPA is used almost exclusively for defining the magnitude of industrial noise. This is the total level of the A-weighted frequency spectrum. A sound level increase of 3 dB is just perceptible subjectively. A 10 dB increase is perceived as a doubling of the loudness.
The following equation holds: These simple equations hold true because the reference levels are selected appropriately. Hydraulic Two different mechanisms are distinguished in hydraulic noises: Turbulent flow causes a broad-band noise.
The velocity profile at the impeller exit is not uniform around the cir- cumference. This results in periodic excitation through impingement on the diffuser vanes or volute cutwaters.
Narrow-band tones are set up with the frequency of the blade passing at the diffuser. These are called blade passing frequencies: The blade passing frequency due to the number of impeller blades predominates mostly. Most important are the 1st, 2nd and 3rd harmonics. Further noises may result from operating the pump in unfavorable conditions, e.
Generally, the noise is lowest near the best efficiency point. The pump maker considers only the pump itself, with pump body, suction and discharge nozzles and baseplate pads.
The user, however, is interested in the overall noise level of the pump installation. This includes additionally the noise from the motor and any gearing plus emissions from pipes and surfaces excited by structure-borne noise. Because the latter depend on the particular installation, they cannot be included in the noise data for a given pump type.
The following methods may be used for measuring pump noise: Sound pressure measurement, prescribed surface method; 2. Sound pressure measurement, reverberation room method; 3. Structure-borne noise measurement; 5. Sound intensity measurement. All these measuring procedures are standardized. Standards in force are tabulated in section 4. For sound pressure measurements, limiting the extraneous noise often requires considerable expense.
A sound-absorbing enclosure for the electric motor and the discharge pipe for sound measurement may be needed on the pump test stand. The structure-borne noise method is insensitive to extraneous noise. However, problems arise from the inexactly known radiation efficiency and from radiating openings where no transducers e. Intensity measurement is the latest method and measures directly the required physical quantity, i.
Extensive sound power measurements have been made on Sulzer pumps, so that sound emission values based on measurements as described below can be quoted for a number of pump types. Note that compared with the sound power levels the sound pressure levels are reduced by the measuring surface see equa- tion 6. A typical frequency pattern is shown by the octave spectrum in Fig. Besides data measured in a Sulzer laboratory a curve from Tourret is plotted. Finally, Fig.
It is clear from this that the noise generation is lowest in the vicinity of the best efficiency point Q Generally speaking, hydraulically well-designed pumps tend to behave well with regard to noise also.
Otherwise it must be remembered that the pump itself often generates relatively little sound power. Other major noise sources are: Water-cooled motors are generally much quieter than air-cooled machines.
Elastic mounting would be best, but this is usually not possible. In any case light structures thin sheets which are not part of the pump fixing should not be joined to foundation supports or via other elements to the pump or driving machinery. As a secondary measure sound-absorbent insulation of the pipes may be considered. Such insulation can reduce noise from pump pipelines by 5 to 15 dB Fig. Sound-absorbent cladding of the pump possibly providing thermal insulation at the same time.
Attainable level reduction up to about 5 dB. Encapsulation sound hoods. Sound hoods bring abatements up to 30 dB and more, depending on their design. It must be borne in mind that the level reduction attainable in the machine room depends also on the radiation from the components mentioned previously pipelines, structure-borne noise.
To ensure the safety of the pump and associated plant components the vibration must be kept within specific limits. If the mechanical state of the pump and its drive are good, the approach flow conditions are reasonably uniform and the duty point is within the allowable range, these limits can be observed without difficulty.
However, if these limits are exceeded or if vibrations markedly increase in the course of time, problems of a mechanical or hydraulic nature may be suspected. Measuring vibrations is therefore a very good way of checking conditions of a pump. On smaller pumps such checking is mostly performed with portable instru- ments. The causes of aggravated vibration are manifold. Detailed measure- ments and analyses carried out by a specialist are often needed for a reliable diagnosis.
Frequency analysis and evaluation is an important step in this diagnostic work. A distinction must be drawn between system- related and pure pump problems.
Typical system-related problems: Unfavorable dynamic behavior of foundations, supporting structures or pipelines e.
Excitation from a component in the pipeline valve, filter, etc. Excitations from the coupling, especially due to misalignment;. Excitations from the drive motor, steam turbine, gearing ;. Unfavorable approach flow conditions like insufficient suction pres- sure cavitation , swirling intake vortex, suction pipe with bends in more than one plane ;.
High-pressure pulsations due to hydraulic instability of the entire system. Typical problems of the pump itself: Mechanical imbalance of the rotating parts due to inexpert balancing, careless assembly or operational influences cavitation erosion, deposits, corrosion, damaged impellers, jammed parts, abrasion ;. Unfavorable dynamic behavior of the rotor due to excessive seal or bearing clearances;.
Increased hydraulic forces when the pump is operated outside of the admissible operation range some increase in vibration is normal when departing from the optimum flow rate ;. Mechanically defective bearings. Vibration on Centrifugal Pumps Figure 4. ISO specifies bearing housing velocity limits for all pumps regardless of bearing type. The relations for a sine-wave signal are given in Fig. Many instruments display the RMS vibration velocity directly, but there are also instruments showing the peak value vp , though its deter- mination is not standardized.
Conversion from vp to vRMS is possible only Figure 4. When documenting a measurement it is therefore very important to state the characteristics of the measuring instrument e. Usually vibrations are measured at both bearing housings in the horizon- tal vertical and axial directions.
On larger pumps with hydrodynamic bearings it is a common practice to measure shaft vibrations, i. The displacement is stated in mm thou- sandths of a millimeter or mils thousandths of an inch. Such measure- ments usually enable the dynamic behavior of the rotor to be judged more directly than by measuring on the bearing housing.
However, shaft vibration measurements can be falsified by shaft non-cylindricality as well as material inhomogeneities. For correct assessment of the mea- sured results, these defaults called mechanical or electrical runout must be known or have only small values.
Often, each bearing is fitted with two transducers at right angles to each other. The orbit of the shaft center can then be plotted Fig. For assessment purposes, therefore, a distinction must be drawn between measured values for individual directions S1, S2 and measured values for the orbit Smax.
The magnitude Smax cannot be calculated from S1 and S2 alone. It is difficult to measure Smax directly but a suitable approximation can be made using one of the methods described in ISO The method most commonly used is to take the maximum value of peak-to-peak displacement measured in two orthogonal direc- tions, X and Y. However, usually vibration standards are applied. The ISO series of standards are widely used to evaluate mechanical vibrations of machines.
Vibration limits for pumps with multi-vane impellers and separate drives i. Table A.
The limits are applicable for each discrete frequency mentioned. Table B. Ratings according to ISO The vibration values are stated for pumps with multi-vane impeller and with separate driver centrifugal, mixed flow or axial flow with rated power above 1 kW.
Sometimes the vibration velocity at the bearing housing is dominated by high-frequency vibration, often corresponding to the number of impel- ler vanes multiplied by the rotation frequency.
In order to judge the rotor behavior it is helpful to filter out these high frequencies. Such high- frequency vibrations may also be falsified by transducer resonances.
Af, 0. See Fig.
There are: Rigid couplings are of the shell or flange type. These are used chiefly where no journal or thrust bearing is provided for the pump or the motor shafts, as is often the case with vertical pumps Fig. The motor bearing at the coupling end then takes over radial guidance of the pump shaft. The axial thrust is also transmitted to the motor shaft, and must be accommodated by the motor bearings.
Flexible couplings are employed in all cases where the drive and pump shafts are supported independently by journal and thrust bearings. These couplings must be capable of accommodating axial, radial and angular misalignments Fig.
For simple cases, i. They also possess a certain torsional elasticity and damping. On pumps with higher speed and power ratings such as boiler feed pumps, gear, flexible membrane and diaphragm couplings are mainly employed Figs 5.
Gear type couplings require lubrication, either by a permanent grease filling or by oil through continuous spray lubrication. The coupling type depends on a large number of factors and needs careful consideration. It must be noted that all couplings transmit axial forces from one shaft to the other if there is relative axial displacement between the two.
Axial forces are transmitted: By forces dependent on torque: With couplings having elastic elements of plastic or rubber Fig.
With gear couplings, by the friction forces on the tooth flanks. With couplings as in Fig. Additional mutual displacement of the shafts alters this axial preload as a function of the axial stiffness of the transmission element. By the axial stiffness of the transmission elements: With diaphragm couplings, by the stiffness of the diaphragm assemblies. On couplings as in Fig. Where there is misalignment as in Fig. Couplings fitted with spacer sleeves are installed to allow for disas- sembly of the shaft seal of the pump, or in case of single-stage pumps to remove the pull-out unit, without removing the driver.
Elastic couplings with appropriate damping elements are used above all where cyclic torsional loading of the shafts due to heavily fluctuating Figure 5.
In such cases careful matching of the coupling characteristic is necessary, entailing calculation of the forced torsional vibration of the entire shaft string. Owing to their mass, shaft couplings affect the rotor dynamic behav- ior. Careful selection of the coupling type and size is therefore extremely important.
Coupling size is normally selected with the maximum torque at normal operation: The choice of coupling is then based on these data. Shaft alignment is vital to the reliability of the coupling.
Accuracy is commensurate with the speed and power rating of the drive and with the type of coupling. In simple cases, alignment with rule and feeler gauge is sufficient Fig. With high-speed machines optical alignment instru- ments must be used to check the mating surfaces and centers for true radial and axial alignment Fig.
On pumps operating at elevated temperatures, allowance for hori- zontal and vertical misalignment is made due to differential thermal expansion of the coupled components e. It is advis- able to check alignment during commissioning, especially, again, for pumps with higher operating temperatures. Bearings Figure 5. Figure 5. Such bearings provide both radial and axial guidance of the shaft. To accommodate larger axial forces, self-aligning roller thrust bearings are often used Fig. Lubrication is with oil or grease, depending on service conditions.
All these sliding contact bearings are hydrodynamic types, deriving their load-bearing capacity from the viscosity of the lubricant.
In nor- mal operation oil-lubricated bearings run with pure fluid friction, i. Sliding contact bearings provide stiffness and damping to the rotor and there- fore are important elements for the rotor dynamic behavior of the pump.
On the other hand, bearings lubricated with the pumped medium frequently operate in the mixed friction range, involving partial contact between the two surfaces.
This calls for a judicious pairing of materi- als if seizure or excessive wear in service is to be avoided. The corrosive properties of the pumped medium must also be taken into account. Oil-lubricated journal bearings are mainly employed in the following types see Fig. Cylindrical bearings are the simplest type of journal bearings and are employed often in multistage pumps running at lower speeds and low to high bearing loads.
Offset halves bearings are cylindrical bearings with shifted bearing halves in the horizontal plane. Multilobe bearings are typically used in high-speed pumps with low bearing loads. Tilting-pad bearings are partial arc types. The pad can tilt on the pivot point to conform with the dynamic loads from the lubricant and shaft.
Such combustion driven pumps directly transmit the impulse from a combustion event through the actuation membrane to the pump fluid. In order to allow this direct transmission, the pump needs to be almost entirely made of an elastomer e.
Hence, the combustion causes the membrane to expand and thereby pumps the fluid out of the adjacent pumping chamber. The first combustion-driven soft pump was developed by ETH Zurich.
The device uses the water hammer effect to develop pressure that lifts a portion of the input water that powers the pump to a point higher than where the water started. The hydraulic ram is sometimes used in remote areas, where there is both a source of low-head hydropower, and a need for pumping water to a destination higher in elevation than the source.
In this situation, the ram is often useful, since it requires no outside source of power other than the kinetic energy of flowing water. A centrifugal pump uses an impeller with backward-swept arms Rotodynamic pumps or dynamic pumps are a type of velocity pump in which kinetic energy is added to the fluid by increasing the flow velocity. This increase in energy is converted to a gain in potential energy pressure when the velocity is reduced prior to or as the flow exits the pump into the discharge pipe.
This conversion of kinetic energy to pressure is explained by the First law of thermodynamics , or more specifically by Bernoulli's principle. Dynamic pumps can be further subdivided according to the means in which the velocity gain is achieved. Positive displacement pumps physically displace fluid, so closing a valve downstream of a positive displacement pump produces a continual pressure build up that can cause mechanical failure of pipeline or pump.
Dynamic pumps differ in that they can be safely operated under closed valve conditions for short periods of time. Radial-flow pumps[ edit ] Such a pump is also referred to as a centrifugal pump. Another type of radial-flow pump is a vortex pump. The liquid in them moves in tangential direction around the working wheel. The conversion from the mechanical energy of motor into the potential energy of flow comes by means of multiple whirls, which are excited by the impeller in the working channel of the pump.
Generally, a radial-flow pump operates at higher pressures and lower flow rates than an axial- or a mixed-flow pump. Main article: Axial-flow pump These are also referred to as All fluid pumps. The fluid is pushed outward or inward and move fluid axially. They operate at much lower pressures and higher flow rates than radial-flow centrifugal pumps. Axial-flow pumps cannot be run up to speed without special precaution. If at a low flow rate, the total head rise and high torque associated with this pipe would mean that the starting torque would have to become a function of acceleration for the whole mass of liquid in the pipe system.
If there is a large amount of fluid in the system, accelerate the pump slowly. The fluid experiences both radial acceleration and lift and exits the impeller somewhere between 0 and 90 degrees from the axial direction. As a consequence mixed-flow pumps operate at higher pressures than axial-flow pumps while delivering higher discharges than radial-flow pumps.
The exit angle of the flow dictates the pressure head-discharge characteristic in relation to radial and mixed-flow. Main article: Eductor-jet pump This uses a jet, often of steam, to create a low pressure. This low pressure sucks in fluid and propels it into a higher pressure region. Gravity pumps[ edit ] Gravity pumps include the syphon and Heron's fountain.
The hydraulic ram is also sometimes called a gravity pump; in a gravity pump the water is lifted by gravitational force and so called gravity pump Steam pumps[ edit ] Steam pumps have been for a long time mainly of historical interest.
They include any type of pump powered by a steam engine and also pistonless pumps such as Thomas Savery 's or the Pulsometer steam pump.
Recently there has been a resurgence of interest in low power solar steam pumps for use in smallholder irrigation in developing countries. Previously small steam engines have not been viable because of escalating inefficiencies as vapour engines decrease in size. However the use of modern engineering materials coupled with alternative engine configurations has meant that these types of system are now a cost effective opportunity. Valveless pumps[ edit ] Valveless pumping assists in fluid transport in various biomedical and engineering systems.
In a valveless pumping system, no valves or physical occlusions are present to regulate the flow direction. The fluid pumping efficiency of a valveless system, however, is not necessarily lower than that having valves. In fact, many fluid-dynamical systems in nature and engineering more or less rely upon valveless pumping to transport the working fluids therein. Meanwhile, the embryonic vertebrate heart begins pumping blood long before the development of discernible chambers and valves.
References Addie, G. Google Scholar Addie, G. Application and construction of centrifugal solids-handling pumps, pp. Google Scholar Agostinelli, A. Google Scholar Biheller, H. Journal of Engineering for Power, July, pp.
Google Scholar British Standards Institution British Standards Institution, London. Google Scholar Carstens, M. Water hammer resulting from cavitating pumps. Civil Engrs. HY6, pp. Google Scholar Cooper, P.
Centrifugal pump theory.