Page 213 - Buried Pipe Design

Design of Pressure Pipes 187

A partial listing of some typical causes of water hammer is given
below.
1. Changes in valve settings (accidental or planned)
2. Starting or stopping of pumps
3. Unstable pump or turbine characteristics

The magnitude of water hammer pressures generated by a given
change in velocity depends on (1) the geometry of the system, (2) the
magnitude of the change in velocity, and (3) the speed of the water-
hammer wave for the particular system.
These variables are expressed quantitatively as

a
H V (4.6)
g
where H surge pressure, feet of water
a velocity of the pressure wave, ft/s
2
g acceleration due to gravity (32.17 ft/s )
V change in velocity of fluid, ft/s
The pressure rise, in pounds per square inch, may be determined by
2
multiplying Eq. (4.6) by 0.43 lb/in per feet of water as follows:
a
P V (0.43) (4.7)
g
The wave speed is dependent upon
1. Pipe properties
a. Modulus of elasticity
b. Diameter
c. Thickness
2. Fluid properties
a. Modulus of elasticity
b. Density
c. Amount of air, and so forth
These quantities may be expressed as
12 K/
a (4.8)

1 (K /E) (D/t) C 1
where a pressure wave velocity, ft/s
K bulk modulus of water, lb/in 2
density of water, slug/ft 3