CIVIL ENGINEERING FORMULAS

336 CHAPTER TWELVE

ECONOMICAL SIZING OF
DISTRIBUTION PIPING

An equation for the most economical pipe diameter for a distribution system for
water is

(12.138)

whereDpipe diameter, ft (m)
fDarcy–Weisbach friction factor
bvalue of power, $/hp per year ($/kW per year)
Qaaverage discharge, ft^3 /s (m^3 /s)
Sallowable unit stress in pipe, lb/in^2 (MPa)
ain-place cost of pipe, $/lb ($/kg)
iyearly fixed charges for pipeline (expressed as a fraction of total
capital cost)
Haaverage head on pipe, ft (m)

VENTURI METER FLOW COMPUTATION

Flow through a venturi meter (Fig. 12.27) is given by

(12.139)

K (12.140)

4

B

2 g

1 (d 2 d 1 )^2

QcKd^222 h 1 h 2

D0.215

fbQ^3 aS

aiHa 

1/ 7

Throat

Throat connection

Main connection Flow-rate scale

Main section

21 °

5

5 °–7°

4

3

2

1

h 1 – h 2

FIGURE 12.27 Standard venturi meter.