Page 164 - Chemical Process Equipment - Selection and Design

136 FLUID TRANSPORT EQUIPMENT

EXAMPLE Clearly the performance curves are well within the recorn-
7.3
Check of Some Performance Curves with the Concept of mended upper limits of specific speed.
Specific Speed (b) The manufacturer’s recommended NPSH of the pump of Figure
(a) The performance of the pump of Figure 7.7(h) with an Sin. 7.7(c) with an 8 in. impeller will be checked against values from
impeller will be checked by finding its specific speed and Eq. (7.15) with S = 7900:
comparing with the recommended upper limit from Figure
7.6(b). Use Eq. (7.12) for N, Q (gprn) 100 150 200
H (fi) 490 440 300
Q (gpm) 100 200 300 NPSH (rnfgr) 10 18 35
H (ft) 268 255 225 NPSH [Eq. (7.1511 7.4 9.7 11.8
N, (calcd) 528 776 1044
N, [Fig. 7.10(a)l 2050 2150 2500 The manufacturer’s recommended NPSHs are conservative.
NPSH 5 7 13

H total head, f t (first stage) H= total head,ft (first stoge)
(a) (b)
cn
2 4,000
a
0’ 3,500
0
5 3,000
3
- 2,500
.-
m
t
VI
6 2,000
L
1,500
VI
2,
.on.
g g 1,000
BQ 900
.u &
c= 800
XK
700000 0 0 00 000 0 0
gscmg g$ $ma,mon N
H= total heod,ft (first stage) H= total head, ft(first stage)
(C) (d)
Figure 7.6. Upper specific-speed limits for (a) double-suction pumps (shaft through impeller
eye) handling clear water at 85°F at sea level, (b) single-suction pumps (shaft through impeller
eye) handling clear water at 85°F at sea level, (c) single-suction pumps (overhung-impeller
type) handling clear water at 85°F at sea level, (d) single-suction mixed- and axial-flow pumps
(overhung-impeller type) handling clear water at 85°F at sea level. (Hydraulic Institute,
Cleveland, OH, 1957).