Civil Engineering Reference
In-Depth Information
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
2
3
0.1
K
90
O
13
1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Flow ratio,
Q /Q
3
1
Fig. 26-21.
Combining flow—branch angle 90
—loss coefficient
K
13
(
Source:
Reference 7; cour-
tesy of the BHR Group Limited)
To avoid cavitation, the cavitation index, should exceed the values in Table 26-5
(page 930) or Table 26-6 (page 931). For example, consider a single-seated globe
valve and the following conditions:
Fluid:
Water
Temperature:
70
F
Vapor Pressure,
P
v
:
0.363 psi
Upstream Pressure,
P
U
:
180 psi
Downstream Pressure,
P
D
:
50 psi
The value for
is
P
P
50
0.36
v
D
0.38
P
P
180
50
U
D
The value attained indicates that cavitation may be a problem and the use of an alter-
nate valve may be necessary. These values provide only a general guideline based on
earlier work for potential cavitation problems and should be used with caution. The
