Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)
Specific Speed and Modeling Laws 15 GPM 0 113 226 337 452 565 678 732 Table 2-4 Tabulated Performance at 4,000 RPM H(ft) 445 443 438 427 412 381 330 298 Eff. % bhp 0 37 28 45 48 52 52 60 70 66 74 73 73 77 72 76 the pump specific speed. To obtain suction specific speed continue from the rotating speed to NPSHR and vertically to the suction specific speed. Pump specific speed is the same for either single-suction or double-suction designs. For estimating the expected pump efficiencies at the best efficiency points, many textbooks have plotted charts showing efficiency as a function of specific speed (N s ) and capacity (GPM). We have prepared similar charts, but ours are based on test results of many different types of pumps and many years of experience. Figure 2-3 shows efficiencies vs. specific speed as applied to end-suction process pumps (API-types). Figure 2-4 shows them as applied to single-stage double-suction pumps, and Figure 2-5 shows them as applied to double-volute-type horizontally split multi-stage pumps. Figure 2-5 is based on competitive data. It is interesting to note that although the specific speed of multi-stage pumps stays within a rather narrow range, the pump efficiencies are very high, equal almost to those of the double-suction pumps. The data shown are based on pumps having six stages or less and operating at 3,560 RPM. For additional stages or higher speed, horsepower requirements may dictate an increase in shaft size. This has a negative effect on pump performance and the efficiency shown will be reduced. As can be seen, efficiency increases very rapidly up to N s 2,000, stays reasonably constant up to N s 3,500, and after that begins to fall off slowly. The drop at high specific speeds is explained by the fact that hydraulic friction and shock losses for high specific speed (low head) pumps contribute a greater percentage of total head than for low specific speed (high head) pumps. The drop at low specific speeds is explained by the fact that pump mechanical losses do not vary much over the range of specific speeds and are therefore a greater percentage of total power consumption at the lower specific speeds.
R0are 2-2. Specific speed and suction specific nomograph.
- Page 2 and 3: CENTRIFIUGAL PUMPS Design & applica
- Page 4 and 5: CENTRIFUGAL PUMPS Design & Applicat
- Page 6 and 7: Contents Preface —..... —......
- Page 8 and 9: ern Pumps, Mine Dewatering Pumps. W
- Page 10 and 11: Stage Pumps. Single-Suction Single-
- Page 12 and 13: Preface When Val and I decided to c
- Page 14 and 15: CENTRIFUGAL PUMPS Design & applicat
- Page 16 and 17: Part 1 Elements of Pump Design
- Page 18 and 19: 1 Introduction System Analysis for
- Page 20 and 21: Introduction 5 Figure 1-2. The syst
- Page 22 and 23: Introduction 7 mate responsibility
- Page 24 and 25: Introduction 9 Figure 1-6. Maximum
- Page 26 and 27: 2 Specific Speed and Modeling Laws
- Page 28 and 29: Specific Speed and Modeling Laws 13
- Page 32 and 33: Specific Speed and Modeling Laws 17
- Page 34 and 35: Specific Speed and Modeling Laws 19
- Page 36 and 37: Specific Speed and Modeling Laws 21
- Page 38 and 39: Figyre 2-7, New pump from model pum
- Page 40 and 41: Specific Speed and Modeling Laws 25
- Page 42 and 43: Specific Speed and Modeling Laws 27
- Page 44 and 45: Impeller Design 29 Figure 3-1. Requ
- Page 46 and 47: Impeller Design 31 Figure 3-4. Capa
- Page 48 and 49: Impeller Design 33 Step 8: Estimate
- Page 50 and 51: Impeller Design 35 Figure 3-7. Volu
- Page 52 and 53: impeller Design 37 (2) 5 , as final
- Page 54 and 55: Impeller Design 39 The vane develop
- Page 56 and 57: Impeller Design 41 Figure 3-12. Are
- Page 58 and 59: impeller Design 43 Figure 3-16. Inf
- Page 60 and 61: 4 General Pump Design It is not a d
- Page 62 and 63: General Pump Design 4? Figure 4-1.
- Page 64 and 65: General Pump Design 49 designed and
- Page 66 and 67: Volute Design 51 Figure 5-1. Volute
- Page 68 and 69: Volute Design 53 Figure 5-2. Radial
- Page 70 and 71: Volute Design 55
- Page 72 and 73: Volute Design 57 Figure 5-4. Effici
- Page 74 and 75: Volute Design 59 Figure 5-5. Typica
- Page 76 and 77: Volute Design 61 Figure 5-8. Univer
- Page 78 and 79: Volute Design S3 Manufacturing Cons
Specific Spe<strong>ed</strong> <strong>and</strong> Modeling Laws 15<br />
GPM<br />
0<br />
113<br />
226<br />
337<br />
452<br />
565<br />
678<br />
732<br />
Table 2-4<br />
Tabulat<strong>ed</strong> Performance at 4,000 RPM<br />
H(ft)<br />
445<br />
443<br />
438<br />
427<br />
412<br />
381<br />
330<br />
298<br />
Eff. %<br />
bhp<br />
0<br />
37<br />
28<br />
45<br />
48<br />
52<br />
52<br />
60<br />
70<br />
66<br />
74<br />
73<br />
73<br />
77<br />
72 76<br />
the pump specific spe<strong>ed</strong>. To obtain suction specific spe<strong>ed</strong> continue from<br />
the rotating spe<strong>ed</strong> to NPSHR <strong>and</strong> vertically to the suction specific spe<strong>ed</strong>.<br />
Pump specific spe<strong>ed</strong> is the same for either single-suction or double-suction<br />
designs.<br />
For estimating the expect<strong>ed</strong> pump efficiencies at the best efficiency<br />
points, many textbooks have plott<strong>ed</strong> charts showing efficiency as a function<br />
of specific spe<strong>ed</strong> (N s ) <strong>and</strong> capacity (GPM). We have prepar<strong>ed</strong> similar<br />
charts, but ours are bas<strong>ed</strong> on test results of many different types of pumps<br />
<strong>and</strong> many years of experience.<br />
Figure 2-3 shows efficiencies vs. specific spe<strong>ed</strong> as appli<strong>ed</strong> to end-suction<br />
process pumps (API-types). Figure 2-4 shows them as appli<strong>ed</strong> to single-stage<br />
double-suction pumps, <strong>and</strong> Figure 2-5 shows them as appli<strong>ed</strong> to<br />
double-volute-type horizontally split multi-stage pumps.<br />
Figure 2-5 is bas<strong>ed</strong> on competitive data. It is interesting to note that<br />
although the specific spe<strong>ed</strong> of multi-stage pumps stays within a rather<br />
narrow range, the pump efficiencies are very high, equal almost to those<br />
of the double-suction pumps. The data shown are bas<strong>ed</strong> on pumps having<br />
six stages or less <strong>and</strong> operating at 3,560 RPM. For additional stages or<br />
higher spe<strong>ed</strong>, horsepower requirements may dictate an increase in shaft<br />
size. This has a negative effect on pump performance <strong>and</strong> the efficiency<br />
shown will be r<strong>ed</strong>uc<strong>ed</strong>.<br />
As can be seen, efficiency increases very rapidly up to N s 2,000, stays<br />
reasonably constant up to N s 3,500, <strong>and</strong> after that begins to fall off<br />
slowly. The drop at high specific spe<strong>ed</strong>s is explain<strong>ed</strong> by the fact that hydraulic<br />
friction <strong>and</strong> shock losses for high specific spe<strong>ed</strong> (low head)<br />
pumps contribute a greater percentage of total head than for low specific<br />
spe<strong>ed</strong> (high head) pumps. The drop at low specific spe<strong>ed</strong>s is explain<strong>ed</strong> by<br />
the fact that pump mechanical losses do not vary much over the range of<br />
specific spe<strong>ed</strong>s <strong>and</strong> are therefore a greater percentage of total power consumption<br />
at the lower specific spe<strong>ed</strong>s.