A velocity as low as 0. There shall be no flow disturbing fittings such as partially open valves, tees, short radius elbows, etc. Fully open, non-flow disturbing valves, vaned elbows, long radius elbows and reducers are not considered flow disturbing fittings refer to Figures 9.
In such cases, a concentric or eccentric reducer is fitted to accommodate the difference in pipe size. For horizontal suction piping, the flat side of an eccentric reducer shall be located on the top. For vertical piping without bends near the pump, a concentric reducer is recommended.
Take-offs directly opposite each other are not allowed. The maximum velocity allowed in the suction header is 2. If the ratio of the take-off diameter to the header diameter is equal to or greater than 0.
If that same ratio is less than 0. Considering the cost for a model study, an evaluation Figure 9. HI Pump Intake Design — is needed to determine if a model study is required.
When evaluating the indirect impacts of inadequate performance or pump failures, the probability of failure may be considered, such as by comparing the proposed intake design to other intakes of essentially identical design and approach flow which operate successfully. The model study shall be conducted by a hydraulic laboratory using personnel that have experience in modeling pump intakes.
Free-surface vortices are detrimental when their core is strong enough to cause a localized low pressure at the impeller and because a vortex core implies a rotating rather than a radial flow pattern. Sub-surface vortices also have low core pressures and are closer to the impeller. Strong vortex cores may induce fluctuating forces on the impeller and cavitation.
Sub-surface vortices with a dry-pit suction inlet are not of concern if the vortex core and the associated swirling flow dissipate well before reaching the pump suction flange.
Pre-swirl in the flow entering the pump exists if a tangential component of velocity is present in addition to the axial component. Swirl alters the inlet velocity vector at the impeller vanes, resulting in undesired changes in pump performance characteristics, including potential vibration.
HI Pump Intake Design — A reasonably uniform axial velocity distribution in the suction flow approaching the impeller is assumed in the pump design, and non-uniformity of the axial velocity may cause uneven loading of the impeller and bearings. A properly conducted physical model study can be used to derive remedial measures, if necessary, to alleviate these undesirable flow conditions due to the approach upstream from the pump impeller. The typical hydraulic model study is not intended to investigate flow patterns induced by the pump itself or the flow patterns within the pump.
The objective of a model study is to ensure that the final sump or piping design generates favorable flow conditions at the inlet to the pump. Also, the model shall be large enough to allow visual observations of flow patterns, accurate measurements of swirl and velocity distribution, and sufficient dimensional control.
Realizing that larger models, though more accurate and reliable, are more expensive, a balancing of these factors is used in selecting a model scale.
However, the scale selection based on vortex similitude considerations, discussed below, is a requirement to avoid scale effects and unreliable test results. Fluid motions involving vortex formation have been studied by several investigators Anwar, H. No specific geometric scale ratio is recommended, but the resulting dimensionless numbers must meet these minimum values. For practicality in observing flow patterns and obtaining accurate measurements, the model scale shall yield a bay width of at least mm 12 inches , a minimum liquid depth of at least mm 6 inches , and a pump throat or suction diameter of at least 80 mm 3 inches in the model.
By this procedure, the circulation contributing to vortices would presumably be increased, resulting in a conservative prediction of stronger vortices. Tests at prototype velocities are not recommended, as this will distort approach flow patterns and unduly exaggerate flow disturbances e.
As the approach flow non-uniformities contribute significantly to the circulation causing pre-swirl and vortices, a sufficient area of the approach geometry or length of piping has to be modeled, including any channel or piping transitions, bends, bottom slope changes, control gates, expansions and any significant cross-flow past the intake.
All pertinent sump structures or piping features affecting the flow, such as screens and blockage due to their structural features, trash racks, dividing walls, columns, curtain walls, flow distributors, and piping transitions must be modeled. Special care should be taken in modeling screens; the screen head loss coefficient in the model shall be the same as in the prototype. The head loss coefficient is a function of the screen Reynolds number, the percent open area, and the screen wire geometry.
Scaling of the prototype screen wire diameter and mesh size to the selected model geometric scale may be impractical and improper due to the resulting low model Reynolds number. In some cases, a model could use the same screen as the prototype to allow equal loss coefficients. Scaling of trash racks bars may also be impractical and lead to insufficient model bar Reynolds number.
Fewer bars producing the same total blockage and the same flow guidance effect bar to space aspect ratio may be more appropriate. The inside geometry of the bell up to the bell throat section of maximum velocity shall be scaled, including any hub located between the bell entrance and the throat. The bell should be modeled of clear plastic or smooth fiberglass, the former being preferred for flow visualization.
The outside shape of the bell may be approximated except in the case of multi-stage pumps, in which case the external shape may affect flow patterns approaching the inlet bell. The impeller is not included in hydraulic models, as the objective is to evaluate the effect of the intake design on flow patterns approaching the impeller. A straight pipe equal to the throat diameter or pump suction diameter shall extend at least five diameters downstream from the throat or pump suction.
For free surface intakes, the model shall provide up to 1. The extent of the measurements is summarized in Section 9. Flow: The outflow from each simulated pump shall be measured with flow meters.
If an orifice or venturi meter conforming to ASME standards is used, the meter need not be calibrated. Liquid Level: Liquid surface elevations shall be measured using any type of liquid level indicator accurate to at least 3 mm 0.
Vortex Type Vortex Type Surface swirl 1 Dye core to intake: coherent swirl throughout water column 3 Free Surface Vortices: To evaluate the strength of vortices at pump intakes systematically, the vortex strength scale varying from a surface swirl or dimple to an air core vortex, shown in Figure 9. Vortex types are identified in the model by visual observations with the help of dye and artificial debris, and identification of a coherent dye core to the pump bell or pump suction flange is important.
Vortices are usually unsteady in strength and intermittent in occurrence. Hence, an indication of the persistence of varying vortex strengths types shall be obtained through observations made at short intervals in the model e. Such detailed vortex observations are needed only if coherent dye core or stronger vortices exist for any test. Photographic or video documentation of vortices is recommended.
HI Pump Intake Design — Sub-surface Vortices: Sub-surface vortices usually terminate at the sump floor and walls, and may be visible only when dye is injected near the vortex core. The classification of sub-surface vortices, given in Figure 9. The possible existence of subsurface vortices must be explored by dye injection at all locations on the wall and floor around the suction bell where a vortex may form, and documentation of persistence shall be made, as for free surface vortices.
Pre-Swirl: Visual observations of the orientation of eight or more equally spaced yarns mounted to form a circle equal to the outer bell diameter and originating about one half the bell floor clearance are useful but not required to evaluate qualitatively any pre-swirl at the bell entrance.
The yarns shall be one half the bellto-floor clearance in length. Swirl in the Suction Pipe: The intensity of flow rotation shall be measured using a swirl meter, see Figure 9.
The swirl meter shall consist of a straight vaned propeller with four vanes mounted on a shaft with low friction bearings. Therefore, swirl meter readings shall be obtained continuously; for example, readings during consecutive intervals of 10 to 30 seconds, covering a period of at least 10 minutes in the model.
Swirl meter rotation direction shall also be noted for each short duration. The maximum short duration swirl angle and an average swirl angle shall be calculated from the swirl meter rotations see Acceptance Criteria below. Swirl at a dry-pit suction inlet is not of concern if the swirl dissipates before reaching the pump suction flange.
Velocity Profiles: Cross-sectional velocity profiles of the approach flow may be obtained using a propeller meter or other suitable device at a sufficient number of measuring points to define any practical skewness in the approach flow.
The cross section location shall be selected to be representative of the approaching flow prior to being influenced by the pump, such as at a distance of two intake widths upstream from the pump centerline. Such measurements are in themselves not critical or required, but allow a better understanding of how the approach flow may be contributing to other flow irregularities and what type of remedial devices may be effective.
To allow velocity fluctuations to be properly measured and recorded versus time, care should be taken that no unnecessary physical or electronic damping is introduced. The angularity of the actual velocity vector relative to the axis of the pump or suction piping shall be observed at three or more locations with dye or strings to ensure that there are no large deviations from axial flow.
The swirl meter rotation should be reasonably steady, with no abrupt changes in direction when rotating near the maximum allowable rate angle. If there are multiple pumps, all possible combinations of operating conditions should be included. Even though vortices are probably most severe at maximum flows and minimum submergence, there are instances where stronger vortices may occur at higher liquid levels and lower flows, perhaps due to less turbulence. Vortex observations and swirl measurements shall be made for all tests.
Axial velocity measurements at the bell throat or suction inlet for each pump in the model are recommended at least for the one test indicating the maximum swirl angle for the final design. Still- photographic documentation of typical tests showing vortexing or other flow problems shall be made.
The initial design shall be tested first to identify any hydraulic problems. If any objectionable flow problems are indicated, modifications to the intake or piping shall be made to obtain satisfactory hydraulic performance. Modifications may be derived using one or two selected test conditions indicating the most objectionable performance.
Practical aspects of installing the modifications should be considered. The performance of the final modified design shall be documented for all operating conditions. If any of the tests show unfavorable flow conditions, further revisions to the remedial devices shall be made.
For intakes with a free surface, most tests shall be at Froude scaled flows; however, a few selected tests for the final design shall be repeated at 1. No velocity measurements shall be conducted at higher than Froude-scaled flows.
It is recommended that representative tests of the final design be witnessed by the user, the pump manufacturer, and the station designer. The report shall contain photographs of the model showing the initial and final designs, drawings of any recommended modifications, and photographs of relevant flow conditions identified with dye or other tracers.
A brief video tape of typical flow problems observed during the tests is recommended. For example, the clearance from the bell to the sump floor and side walls and the distance to various upstream intake features is controlled in these standards by expressing such distances in multiples of the pump or inlet bell diameter. Such standardization of conditions leading to, and around, the inlet bell reduces the probability that strong submerged vortices or excessive pre-swirl will occur.
Also, the required minimum submergence to prevent strong free-surface vortices is related to the inlet bell or pipe diameter see Section 9. HI Pump Intake Design — If the pump or pipe suction inlet diameter D has been selected prior to designing the sump, then the sump design process see Table 9. However, only the use of inlet sizes within the guidelines provided in this section will produce sump dimensions that comply with these standards. Use of bell or inlet diameters outside the range recommended herein will also comply with these standards if a hydraulic study is conducted in accordance with Section 9.
If the pump or pipe suction inlet has not been selected, it is recommended that the inlet bell diameter be chosen based on achieving the bell inlet velocity that experience indicates provides acceptable inflow conditions to the pump. The bell inlet velocity is defined as the flow through the bell i. Information on acceptable average bell inlet diameter velocities is provided in Figure 9. The solid line represents the average pump bell diameter from the survey, corresponding to a bell inlet velocity of 1.
These permissible ranges in inlet bell velocity are given in Table 9. Although the survey indicated that pumps with bells outside this range may be proposed, experience indicates that inlet bell or inlet pipe velocities higher than the recommended range are likely to cause hydraulic problems.
Use of lower velocities would produce unnecessarily large pump bells or inlet pipes and, therefore, sumps. For sump design prior to pump selection, the recommended inlet bell diameter shown on Figure 9.
This recommended bell diameter is based on an inlet velocity of 1. This process will allow the sump design to proceed. An inlet bell diameter within this range will produce a sump geometry that complies with these standards on minimum submergence and sump dimensions, without changing the sump design based on the recommended inlet bell diameter.
Submerged vortices are not believed to be related to submergence and are not considered in this section. If a submergence greater than recommended herein is needed to provide the required NPSH for the pump, that greater submergence would govern and must be used. Approach-flow skewness and the resulting circulation have a controlling influence on free-surface vortices in spite of adequate submergence. Due to the inability to predict and quantify approach flow characteristics for each particular case without resorting to hydraulic model studies, and the lack of available correlation between such characteristics and vortex strength, the recommended minimum submergence given herein is for a reasonably uniform approach flow to the pump suction bell or pipe inlet.
Highly non-uniform skewed approach flows will require the application of vortex suppression devices not part of this standard such as those offered for information in Appendix A. Such devices can be more practical in suppressing vortices than increased submergence. Even for constant flows, vortices are not steady in position or strength, usually forming and dissipating sporadically.
This is due to the random nature by which eddies merge to form coherent circulation around a filament and by which turbulence becomes sufficient in intensity to disrupt the flow pattern. HI Pump Intake Design — given conditions, and this process is enhanced by defining a measure of vortex strength, as illustrated in Figure 9. HI Pump Intake Design — For a given geometry and approach flow pattern, the vortex strength would only vary with the remaining parameters, that is range of inlet bell diameters and velocities at a given flow recommended in Section 9.
Thus, Equation 9. FD would contain a family of curves, each representing different values of vortex strength, VT refer to Figure 9. Application considerations For a given flow, Q, an inlet diameter may be selected in accordance with Section 9. This is reasonable, since the inlet velocity flow provides the energy to cause a potentially greater vortex strength if the relative submergence were not increased.
The relative submergence would only be constant if the Froude number for various inlets were constant. Information collected by the Hydraulic Institute not included herein shows that the average inlet Froude number for bells of typical pump applications is not constant, and that a range of Froude numbers would be possible at a given design flow. The above illustrates that the actual submergence depends on the selection of D for a given flow.
As D increases, the first term causes an increase in submergence, whereas the second term causes a decrease. These opposing trends imply a minimum value of S at some D for a given flow, and differentiating S with respect to D, allows determining that value. However, for the range of recommended bell diameters in Section 9. For the inlet bell design diameter recommended in Section 9. This figure also shows the recommended minimum submergence for the limits of the bell diameter that comply with these standards, see Figure 9.
HI Pump Intake Design — 6. HI Pump Intake Design — diameter is needed, as long as the final selected bell diameter is within the limits that comply with these standards. Terms 9. Air Core Vortex A vortex strong enough to form an elongated core of air see type 6, Figure 9. Anti-Rotation Baffle Device used to inhibit the rotation of fluid at or near the suction. Approach Channel A structure that directs the flow to the pump. Approach pipe A pipe laid at a gradient sufficient to cause super-critical flow and used to contain a portion of the active storage requirement for a constant speed pump.
Backwall A vertical surface behind the inlet to a suction fitting. Backwall Clearance The distance between the backwall and the point of closest approach of the suction fitting. Backwall Splitter A device formed or fabricated and attached to the backwall that guides the movement of flow at or near a suction. Baffles Obstructions that are arranged to provide a more uniform flow at the approach to a pump or suction inlet.
Bay A portion of an intake structure configured for the installation of one pump. Bell The entrance to an axial flow pump or the flared opening leading to pump inlet piping.
Benching A type of fillet used to minimize stagnant zones by creating a sloping transition between vertical and horizontal surfaces. Benching is applied between sump walls and the sump bottom, or between the back wall and the sump bottom. Cell A structure intended to confine the liquid approaching the intake to a pump see Bay.
Check Valve Piping component used to prevent reverse flow. Circular Well A suction chamber circular in shape in plan. Curtain Wall A near vertical plate or wall located in an intake that extends below the normal low liquid level to suppress vortices. Double Suction Impeller An impeller provided with a single suction connection that separates and conveys the fluid to two suction areas.
Dry-Pit Suction Suction from a well that conveys fluid to a pump located in a non-wetted environment. Dual Flow Screens Screening that provides two flow paths for liquid, not in-line with the main flow. Eddy A local rotational flow pattern disturbing regular streamlines a vortex. End Suction Pump A pump that has a suction flange coaxial to the impeller shaft and the pump volute is usually not submerged in the sump.
Fillet A triangular element at the vertex of two surfaces to guide the flow. Floor Clearance The distance between the floor and the suction bell or opening. Floor Cone A conical fixture placed below the suction between the floor and the suction bell. Flow Straighter Any device installed to provide more uniform flow. Forebay The region of an intake before individual partitioning of flow into individual suctions or intake bays. Formed Suction Intake A shaped suction inlet that directs the flow in a particular pattern into the pump suction.
Free Surface Flow Open channel or unconfined flow. Froude Number A dimensionless grouping of parameters used in flow analysis and modeling that indicates the relative influence of inertial compared to gravitational forces see Equation 9. Guide Vanes Devices used in the suction approach that directs the flow in an optimal manner.
Hydraulic Jump A turbulent sudden increase in liquid depth as the flow decelerates from super-critical to sub-critical flow. Intake Velocity The average or bulk velocity of the flow in an intake. Mixer A mechanical device that produces an axial propeller jet, often used for maintaining suspension of solids-bearing liquids in wet wells and tanks. Mixing Nozzles Nozzles attached to the pump volute or the discharge pipe designed to mix solids in a wet well.
Multiplex Pumping Pump installations where sets of pumps are used, such as duplex two or triplex three. Physical Hydraulic Model A reduced-scale replicate of the geometry that controls approach flow patterns operated according to certain similitude laws for flow, velocity and time. Piping Reducer Any change in pipe size, or line area, that results in either an increase or decrease in velocity. Pre-swirl Rotation of the flow at the pump suction due to the approach flow patterns. Pump A device used to convey fluid from a low-energy level to a higher one.
Pump Column Part of the pump assembly that both connects the pump to the discharge head and nozzle and conveys fluid into the system. Pump Suction Bell A part of the pump that provides an opening to convey flow into the suction eye of the impeller. Rectangular Wet Well Any wet well in which pumps are arranged along a wall opposite the influent conduit. The shape may be square, rectangular or trapezoidal. Reynolds Number A dimensionless grouping of parameters used in flow analysis and modeling that indicates the relative influence of inertial compared to viscous forces see Section 9.
Scale Effect The impact of reduced scale on the applicability of test results to a full-scale prototype. Sediment Settleable materials suspended in the flow. Septicity A condition in which stagnant domestic sewage turns septic due to a lack of oxygen.
Snoring refers to the gurgling sound associated with continuous air entrainment. Solids Material suspended in the liquid. Specific Energy Pressure head plus velocity head referenced to the invert of a conduit.
Specific Speed Equivalent to a dimensionless number, a high value denotes a high-flow — low-head pump while a low value denotes a low-flow — high-head pump. Soffit Inside top of a pipe. Sequent Depth The depth of liquid following a hydraulic jump. Submergence The height of liquid level over the suction bell or pipe inlet. Submersible Pump A close coupled pump and drive unit designed for operation while immersed in the pumped liquid. Suction Head Pressure available at the pump suction, usually positive if the liquid level is at a higher elevation than the pump suction.
Suction Lift Negative pressure at the pump suction, usually a result of the liquid level being at a lower elevation than the pump suction. Suction Scoop A device added to the suction to change the direction of flow. Refer to Formed Suction Intake. Suction Strainer A device located at the inlet to either protect the pump or provide flow stability at the suction.
Sump A pump intake basin or wet well. See Forebay. Swirl Rotation of fluid around its mean, axial flow direction. Swirl Angle The angle formed by the axial and tangential circumferential components of a velocity vector see Equation 9.
Swirl Meter A device with four flat vanes of zero pitch used to determine the extent of rotation in otherwise axial flow. Trench Intake An intake design that aligns the pump suctions in-line with, but below, the inflow. A type of forebay. Turning Vanes Devices applied to the suction to alter the direction of flow.
Unitized Intake A multiple pump intake with partitioned pump bays. Vane See Floor Vane. Volute The pump casing for a centrifugal type of pump, generally spiral or circular in shape. Vortex A well-defined swirling flow core from either the free surface or from a solid boundary to the pump inlet see Figure 9. Vortex, Free Surface A vortex that terminates at the free surface of a flow field. Vortex, Subsurface A vortex that terminates on the floor or side walls of an intake.
Wall Clearance Dimensional distance between the suction and the nearest vertical surface. HI Pump Intake Design — Terms Definition Wastewater Description of fluid that typically carries suspended waste material from domestic or industrial sources. Weber Number A dimensionless grouping of parameters used in flow analysis and modeling that indicates the relative influence of inertial compared to surface tension forces see Section 9.
Wet-Pit Suction A suction with the pump fully wetted. Wet Well A pump intake basin or sump having a confined liquid volume with a free water surface designed to hold liquid in temporary storage to even out variations between inflow and outflow. Definition A Distance from the pump inlet centerline to the intake structure entrance Fig. B-1 Flow scale in model Eq. B-1, Eq. B-2, Eq. B-3 Flow rate for pump no. B-2, Fig. B-2, B-3 Time scale of model Eq. B-1 Vol1 Vol2 Active sump volume for pump no.
B-2, B-3 Active sump volume for pump no. HI Pump Intake Design — Appendix A Remedial Measures for Problem Intakes This appendix is not part of this standard, but is presented to help the user in considering factors beyond the standard sump design.
A-1 Introduction The material presented in Appendix A is provided for the convenience of the intake design engineer in correcting unfavorable hydraulic conditions of existing intakes. None of the remedial measures described herein are part of the standard intake design recommendations provided in Section 9. A portion of the material in Appendix A transmits general experience and knowledge gained over many years of improving the hydraulics of intake structures, and such educational material may not include the specific recommendations appropriate for a standard.
Corrections described herein have been effective in the past, but may or may not result in a significant improvement in performance characteristics for a given set of sitespecific conditions. Other remedial fixes not provided herein may also be effective, and a hydraulic model test is needed to verify whether a given remedial design feature results in acceptable flow conditions. This is particularly true because adding a remedial feature to solve one flow problem may have detrimental effects on other flow phenomena of concern.
Appendix A concentrates on rectangular intakes for clear liquids, but the basic principles can be applied to other types of intakes. The material is organized by the general type of hydraulic problem in an upstream to downstream direction, since proper upstream flow conditions minimize downstream remedial changes. A-2 Approach flow patterns The characteristics of the flow approaching an intake structure is one of the foremost considerations for the designer.
Unfortunately, local ambient flow patterns are often difficult and expensive to characterize. Even if known, conditions are generally unique, frequently complex, so it is difficult to predict the effects of a given set of flow conditions upstream from an intake structure on flow patterns in the immediate vicinity of a pump suction.
Several typical approach flow conditions are shown in Figure A. Figure A. The ideal conditions, and the assumptions upon which the geometry and dimensions recommended for rectangular intake structures in this section are based, are that the structure draws flow so that there are negligible ambient currents cross-flows in the vicinity of the intake structure that create asymmetrical flow patterns approaching any of the pumps, and the structure is oriented so that the boundary is symmetrical with respect to the centerline of the structure.
Recommendations based on a physical hydraulic model study for analyzing departures from the ideal condition are given in Section 9. HI Pump Intake Design — more favorable flow conditions than found in open sumps. Open sumps, with no dividing walls, have been used with varying levels of success, but adverse flow patterns can frequently occur if dividing walls are not used. The trench-type intake structure, described in Section 9. Open sumps are particularly susceptible to cross-currents and non-uniform approach flow patterns.
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PDF Price. Not a Member? This standard is not included in any packages. We have no document history for this standard. Appendix E Index. Post on Nov 1. Category: Documents download. Tags: standards developer americannational standard hydraulic instituteall design objectives19 substantial agreement sylvan wayparsippany title page inlet bell design diameter. This page intentionally blank. Sections 9. ANSI Yes ANSI N2. The Breeze 9.
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