MIL-HDBK-1022

Tc

=

2L/a = 22,000/3,692 = 1.08 seconds

From the table of values for "a", the surge pressure

wave velocity (a) is 3,692 fps (1125.3 m/s). The maximum

pressure in any pipeline occurs when the total discharge is

stopped in a period of time equal to or less than the critical

time. Since the valve will theoretically close prior to this,

Equation (2) should be used to determine the pressure rise.

In this case, the final velocity (Vo) will be assumed to be

zero because the critical time is greater than the valve

closure time.

P1 - P = (V1wa)/(144g)

= (6.8151.53,692)/(14432.2) = 279 psig (1925

kPa)

P1 = P+273 = 60+279 = 339 psi (2337 kPa)

Initial velocity (V1) was found by dividing the given

flow rate of 600 gpm (38 L/S) by the cross sectional area of

the 6-inch (150 mm) diameter, Schedule 40 pipe.

Considerations will have to be made for this system to deal

with the maximum predicted pressure.

(4) When the valve closure time is longer than

the critical time, the surge will be less than predicted by

Equation (2). The equation used to calculate surge pressure

rise for this situation is:

EQUATION: P1 - P = [2Lw (V1 - VC)]/(CgT1.3)

(3)

where:

P1 = maximum pressure (psig or Pa)

P = pump shutoff pressure (psig or Pa) (equal to

system static pressure)

L = length of pipe (ft or m)

V1 = initial velocity (fps or m/s)

VC = velocity at TC (fps or m/s)

w = specific weight of the fluid (lbm/ft3 or kg/m3)

g = gravitational constant (32.2 ft/s2 or 9.81 m/s2)

C = unit constant (144 in2/ft2, 0.101 (kg/m2)/Pa

a = surge pressure wave velocity (fps or m/s)

T = valve closure time (sec)

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