maximum and minimum; delivery pressure, maximum and minimum; system

temperature, maximum and minimum; flow-control requirements. The preliminary

fluid flow calculations are based on estimates of piping size and component

location. The use of simplified fluid flow calculations is described in this

section. (Detailed flow calculations, made after design information is more

complete, are described in Section 5, Paragraph 4.)

NOTE:

The designer should note that Section 5, Paragraph 4,

provides a reference for making detailed flow calculations.

The designer should review that reference so

he will not be misled by the brevity of the section

into thinking the procedure in itself is short or simple.

(1) Fluid Flow Approximations. The piping configuration must

initially be approximated for each system to provide the required flow rate.

This requires an estimate of the piping arrangements and of the locations and

types of valves and fittings. The basic problem becomes one of selecting the

smallest pipe size for each system that does not cause an excessive pressure

drop. Excessive pressure drop in piping containing a liquid can result in

cavitation as well as require excessive pumping pressure (requiring an

expensive pump or high-strength pipe), while excessive pressure drop in

piping containing a gas can result in excessive noise or insufficient

capacity if sonic flow is encountered. (Thus, "excessive" will be defined by

the designer within the context of the system.) Using a larger pipe size

will reduce the noise of the fluid flow. The Piping Handbook by Crocker and

King (Reference 14) and the Crane Company Technical Paper No. 410, Flow of

Fluids Through Valves, Fittings, and Pipe (Reference 15), as well as other

sources of the designer's choice, provide guidance for making fluid flow

calculations. The initial sizing of a fluid system can be accomplished

through the use of Darcy's formula (Reference 15) and the use of selected

tables and simplified calculations.

(2) Darcy's Formula. Darcy's formula expresses the pressure drop

resulting from fluid friction in a pipe. In use of this formula, pressure

drop through valves and fittings is expressed in terms of pipe length. One

form of this formula is the following equation:

fL

[rho]V2

[DELTA]P = --

---------

(1)

D

2g144

where:

[DELTA]P

=

pressure drop, psi

f

=

Moody friction factor

L

=

length of pipe, feet

[rho]

=

fluid weight density, pounds/feet3

V

=

mean flow velocity, feet/second

g

=

acceleration of gravity, 32.2 feet/second

D

=

pipe diameter inches.

(a) Friction factor. The friction factor, f, in Equation

(1) is an experimentally determined value which varies in accordance with

several fluid properties. For approximation purposes it is convenient and

conservative to assume that complete turbulence exists in the fluid system.

For this condition, f can be obtained from Figure 5-1 using only the

appropriate inside pipe diameter. Values for f will normally range from

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