Ancient and Modern Engineering and the Isthmian Canal

Table XVII

TABLE OF VALUES OF f AND c.

LEGEND:

(A) = Diameter, Inches.

(B) = Hydraulic Radius r, Inches.

(C) = Velocity, Feet per Second.

(D) = Coefficient c.

(E) = Coefficient f.

Authority.	Pipe-line	(A)	(B)	(C)	(D)	(E)
Darcy	New Pipe	3.22	.8	0.29	78.5	.0418
				10.71	100.0	.0257
Darcy	Old cast-iron pipe	9.63	2.41	1.00	72.5	.0489
	lined with deposit			12.42	74.0	.0468
Darcy	Pipe above cleaned	9.63	2.41	0.91	90.0	.0316
				14.75	98.0	.0269
Brush	Cast-iron pipe tar-coated	20	5	2.00	114.0	.0197
	and in service 5 years.			3.00	110.0	.0214
Darrach	Cast-iron pipe in service	20	5	2.71	67.5	.0568
	11 years			5.11	83.0	.0376
Darrach	Cast-iron pipe in service	36	9	1.58	60.0	.0716
	7 years			2.37	66.0	.0586

Obviously it is not possible to clean the smaller pipes of a distribution system, but large cast-iron conduits may be emptied at suitable periods and have their interior surfaces cleaned of tubercles or other accumulations. At the same time, if necessary, a new coal-tar coating can be applied.

Table XVIII exhibits the values of the coefficient c to be used in Chezy’s formula for new and clean coated cast-iron pipes. It represents the results of actual hydraulic experience and is taken from Hamilton Smith’s “Hydraulics.” A comparison between this table and that which precedes will show how serious the effect of tubercles may be on the discharging capacity of a cast-iron pipe.

In using Chezy’s formula, v = c√rs, in connection with either Table XVII or XVIII, the slope or sine of inclination s of the hydraulic gradient may be readily computed by equation (10), which gives the head lost by friction in a closed circular pipe as

h = f -	l	=	v²	.
	d		2g

It is only necessary in a straight pipe or one nearly straight to compute the quantity

s =	h	=	f		v²	.
	l		d		2g