MIL-HDBK-1022

b) Most systems designed in accordance with this

manual will have ANSI Class 150 flanges and a maximum

allowable working pressure of 285 psig (2000 kPa) at 100

degrees F (38 degrees C) for carbon steel and 275 psig (1900

kPa) at 100 degrees F (38 degrees C) for stainless steel

systems. This means that the total pressure including surge,

pump shutoff pressure, and static pressure in any part of the

system should never exceed those maximum allowable working

pressures. Other equipment items such as tank trucks,

aircraft fuel tanks, or shipboard fuel tanks which may be

damaged by shock pressures may require lower maximum surge

pressure. Assume a near instantaneous shut-off by the

aircraft in the design of aircraft hydrant systems.

c) Do not use manual calculations instead of

computer modeling when system surge pressures are crucial and

the piping system is complex. However, for simple piping

systems that operate under 80 psi (550 kPa), use the following

calculations to ascertain if surge is a problem:

(1) Determine the critical time of the system.

This is defined as the time it takes for the first increment

of the pressure wave to travel upstream, reflect, and return

to the valve. Use the following equation:

EQUATION: Tc = 2L/a

(1)

where:

Tc =

critical closure time of system(s)

L=

length of pipe (ft or m)

a=

surge pressure wave velocity (fps or m/s)

Values for "a" for liquid petroleum in schedule 40

steel pipe are as follows. These values are based on

hydrocarbons with a specific gravity of 0.8 at a temperature

of 68 degrees F (20 degrees C):

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