JOHN PARMAKIAN
8.91
SECTION 8.3
WATERHAMMER
Waterhammer is a very destructive force that exists in any pumping installation where
the rate of flow changes abruptly for various reasons. Most engineers recognize the exis-
tence of waterhammer, but few realize its destructive force. Much time and expense have
been spent repairing pipelines and pumps damaged by waterhammer. It is thus essential
for an engineer to be able to know when to expect waterhammer, how to estimate the pos-
sible maximum pressure rise, and, if possible, how to provide means to reduce the maxi-
mum pressure rise to a safe limit.
The computational procedures used for the analysis of waterhammer in pump dis-
charge lines with electric-motor-driven pumps have been known for many years, begin-
ning with the basic waterhammer contributions by Joukousky and Allievi. This work was
followed in later years by many applications of numeric, graphic, and computer tech-
niques. Although the theory and mechanics of computing waterhammer in pump dis-
charge lines have advanced rapidly in recent years, there are many practical aspects of
this subject that are still confusing to engineers. It is the purpose of this section to bring
these to the reader's attention. The first and major portion of the section contains a dis-
cussion of some practical aspects of waterhammer control devices used in pumping plants;
the second indicates the source of various charts that provide ready waterhammer solu-
tions for a variety of these control devices.
NOMENCLATURE ____________________________________________________
The following is a list of variables commonly used in waterhammer computations. The SI
conversion factors for these terms are to be found in Table 1.
a velocity of pressure wave, ft/s
D inside diameter of conduit, ft
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CHAPTER EIGHT
TABLE 1 SI conversions
To convert
To
Multiply by
GD2 (kg m2)
WR2 (lb ft2)
23.73
kg/m2
lb/ft2
0.2048
kg/m3
lb/ft3
0.06243
m
ft
3.281
m/s
ft/s
3.281
m/s2
ft/s2
3.281
m3/s
ft3/s
35.32
mm
ft
3.281 103
e thickness of pipe