Specifications, centrifugal pumps

You must chose a centrifugal pump to pump a coal slurry. You have determined that the pump must deliver 200 gpm at a pressure of at least 35 psi. Given the pump characteristic curves in Appendix H, tell which pump you would specify (give pump size, speed, and impeller diameter) and why What is the efficiency of this pump at its operating point, what horsepower motor would be required to drive the pump, and what is the required NPSH of the pump The specific gravity of the slurry is 1.35. 

All types of equipment, exposed to fluids in motion, are subject to the erosion-corrosion phenomena. This can include pipeline networks (particularly curves, elbows and T-squares), floodgates, pumps, centrifugal fans, helixes, wheels of turbine, tubes of intersections of heat exchangers and measuring devices. In many cases, failures due to erosion-corrosion occur in a relatively short time.16 Most metals are susceptible to erosion-corrosion in the liquid phase under specific conditions. Resistance of metals depends on the physical and chemical properties of the corrosion product and/or the... 

Related Calculations. Use this procedure for any liquid-water, oil, chemical, sludge, etc.—whose specific gravity is known. When liquids other than water are being pumped, the specific gravity and viscosity of the liquid must be taken into consideration. The procedure given here can be used for any class of pump—centrifugal, rotary, or reciprocating. 

The pump (3) is directly coupled to a 5.5 kW-AC motor (2), A conventional centrifugal pump, having specifications di=l34.5 mm, d2=210 mm, bi=31 mm, b2=l9 mm, (31=40, 2=34, 2=7 (backward curved), was used in the experiments. Both closed and open impellers, which have the same specifications, were employed in the tests. A Siemens motor driver (1)... 

From the relationship of the flow ratio to the efficiency ratio, it is established that the flow ratio for this efficiency ratio is 5.3 indicating that an increase of less than 20 per cent in flow through the mainstage is required to achieve the operation of this system with the vented tank. This particular example shows the importance of the concept of the jet pump-centrifugal pump combination when specifications of the type herein considered are encountered. 

Production and Shipment. Estimated adiponitrile production capacities in the U.S. in 1992 were about 625 thousand metric tons and worldwide capacity was in excess of lO metric tons. The DOT/IMO classification for adiponitrile is class 6.1 hazard, UN No. 2205. It requires a POISON label on all containers and is in packing group III. Approved materials of constmction for shipping, storage, and associated transportation equipment are carbon steel and type 316 stainless steel. Either centrifugal or positive displacement pumps may be used. Carbon dioxide or chemical-foam fire extinguishers should be used. There are no specifications for commercial adiponitrile. The typical composition is 99.5 wt % adiponitrile. Impurities that may be present depend on the method of manufacture, and thus, vary depending on the source. 

Selection of pump for a given appHcation is not a trivial task. Often more than one pump type can accomplish the required job. Thus a final choice on a pump type is often a result of personal experience and usage history. As a rule of thumb, the choice of a kinetic, such as centrifugal, or a positive displacement pump is made on the basis of the specific speed. Whereas specific speed is appHcable primarily for centrifugal but not positive displacement pumps, the US value can be used as a guide. Generally, for calculated values of specific speed, eg, nS > 10 [NS > 500), kinetic-type pumps are usually selected. For nS < 10 [NS < 500), positive displacement pumps are typically appHed. 

From the definition of specific speed (eqs. 9 and 10), it follows that reciprocating pumps operate at high pressures and low flow rates. Conversely, centrifugal pumps are appHed at lower pressures and higher flow rates. Many rotary pumps are selected for viscous Hquids having pressures equal to or less than, and capacities lower than, centrifugal pumps. However, these limits are relative and a gray area exists as some pump types cross boundaries into the domain of other types. 

Specification for Hori2ontal End Suction Centrifugal Pumps for Chemical Process," ASME B73.1M, Washington, D.C., 1991. 

R. Hart, Best Practice Centrifugal Pumps. NPSH Definitions and Specifications, Du Pont Internal Specification, Wilmington, Del., May 18,1992. 

This specification covers horizontal, end suction, vertically split, single-stage centrifugal pumps with top centerline discharge and hack pullout feature. 

Development The following discussion relates specifically to the use of what could be called radial-inflow, centrifugal-pump power-recovery turbines. It does not apply to the type of unit nurtured by the hydroelecti ic industry for the 1 ge-horsepower, large-flow, low- to medium-pressure differential area of hydraulic water turbines of the Felton or Francis runner type. There seems to have been little direct transfer of design concepts between these two fields the major manufacturers in the hydroelectric field have thus far made no effort to sell to the process industries, and the physical arrangement of their units, developed from the requirements of the hydroelectric field, is not suitable to most process-plant applications. 

Textile motors Crane motors Determining the size of motor Sugar centrifuge motors Motors for deep-well pumps Motors for agricultural application Surface-cooled motors Torque motors or actuator motors Vibration and noise level Service factors Motors for hazardous locations Specification of motors for Zone 0 locations Specification of motors for Zone I locations Motors for Zone 2 locations Motors for mines, collieries and quarries Intrinsically safe circuits, type Ex. f Testing and certifying authorities Additional requirements for ciritical installations Motors for thermal power station auxiliaries Selection of a special-purpose motor... 

The majority of centrifugal pumps have performance curves with the aforementioned profiles. Of course, special design pumps have curves with variations. Eor example, positive displacement pumps, multi-stage pumps, regenerative turbine type pumps, and pumps with a high specific speed (Ns) fall outside the norm. But you ll find that the standard pump curve profiles are applicable to about 95% of all pumps in the majority of industrial plants. The important thing is to become familiar with pump curves and know how to interpret the information. 

API mandates that the pressure drop across a clean filter element be no more than 15% of the allowable pressure drop when dirty. An upper limit of 5 psi drop is set for clean filters. This is a reasonable criterion. If a little arithmetic is performed, the head rise for a centrifugal pump may be calculated. The specifications on both of these items must be coordinated and made compatible. 

Cavitation of a centrifugal pump, or any pump, develops when there is insufficient NPSH for the liquid to flow into the inlet of the pump, allowing flashing or bubble formation in the suction system and entrance to the pump. Each pump design or family of dimensional features related to the inlet and impeller eye area and entrance pattern requires a specific minimum value of NPSH to operate satisfactorily without flashing, cavitating, and loss of suction flowt... 

The specific speed of a centrifugal pump correlates the basic impeller types as shown in Figure 3-47. 

Figure 3-48. Upper limits of specific speeds for single suction overhung impeller pumps handling dear water at 85°F at sea level. (By permission, Hydraulic Institute Standards for Centrifugal, Rotary, and Reciprocating Pumps, Hydrauiic Institute, 13th ed., 1975.)...

Figure 3-50. Typical centrifugal pump characteristic curve vrith auxiliary specific speed curve. Double-suction, single-stage, 6-in. pump, operating at 1760 rpm constant speed. (By permission, Karassik, I. and Carter, B., Centrifugal Pumps, McGraw-Hill Book Co., inc., 1360, p. 197.)...

Hallam,J. L., Centrifugal Pumps Which Suction Specific Speeds are Acceptable , Hydrocarbon. Processing, 61, No. 4, 1982. 

Application. (Very necessary for special motors and desirable for all others especially large motors driving centrifugal and reciprocating pumps and compressors. Advise whether these start under load. If a replacement and previous motor have failed frequently, give all details and reconsideration of electrical specifications as in order)... 

Figure 3-65 gives the upper limits of specific speeds of single-stage, single and double-suction centrifugal pumps handling clear water at 85°F at sea level [22]. 

Figure 3-67 gives the approximate relative impeller shapes and efficiency variations for various specific speeds of centrifugal pumps. 

Table 3-26 gives the specific speeds for various centrifugal pump types. Table 3-27 gives the suction specific speed ratings for single-suction and double-suction centrifugal pumps. These tables are for pumps handling clear water. 

For the centrifugal pump, two terms are in common use, the Thoma cavitation number cr and the suction specific speed Sn ... 

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