Surge Calculations
Surge Calculations
Surge Calculations
Computations
What is a Surge
A pressure surge or a water
hammer is a pressure wave caused
by a sudden change in water
velocity.
The word water hammer
originates from the hammering
sound which plumbing makes
inside a house when faucets are
turned on or off quickly.
Critical time
Critical time = 2L/a
Valve or pump closure should be
greater than critical
The last 20% of valve closure most
critical. Very dependent on type of
valve.
Simple Valve
Closure
4720
k D
1 * *(1u 2 )
E e
L
L1 L2
Ln
.....
a1 a1 a2
an
Ln
a
n
Branching Pipelines
P3
P1(2a1a2 A1)
(a2a3 A1 a1a3 A2 a1a2 A3)
Pressure Rating
Pressure rating can changed
based on hoop stress and number
of cycles
10000
1000
1000
10000
100000
540000
Cycles to Failure
10000000
100000000
Example
Compute the head increase due to
instantaneous stoppage of water initially
flowing at 5.0 fps in an 10 inch, 80 psi, PIP
pieline, a = 860
If the static head at the point of stoppage is
55.0 psi, what is the total pressure acting on
the pipe at the moment of stoppage?
What is the hoop stress developed at the
moment of stoppage?
Hs=P*D/2*t
If this Hoop stress will occur twice each day,
and at each occurrence there are 8 stress
cycles of this approximate magnitude, and if
the irrigation season is 90 days long, how
Summary
Actual surge analysis is generally much
more complicated than the simple
example.
The most practical method of solutions
is to understand the available protection
hardware and to install that equipment
at enough locations and with reasonable
settings.
A fact of life which makes this approach
almost necessary is that irrigation
systems tend to be added to or changed