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 _l v²_ _h_ = _f_ - --- ----. _d_ 2_g_ It is only necessary in a straight pipe or one nearly straight to compute the quantity _h f v²_ _s_ = --- = --- ------. _l d_ 2_g_ TABLE XVIII. ____ VALUES OF _c_ IN FORMULA: _v_ = _c__√_rs_. --------+------+-------+-------+-------+-------+-------+------- Velocity| Diameters in Feet (_d_ = 4_r_). _v_, | Feet per|------+-------+-------+-------+-------+-------+------- Second.| .05 | .1 | 1 | 1.5 | 2 | 2.5 | 3 --------+------+-------+-------+-------+-------+-------+------- 1 | | 80.0 | 96.1 | 102.8 | 108.8 | 112.7 | 116.7 2 | 77.8 | 88.9 | 104.0 | 110.9 | 116.2 | 120.3 | 123.8 3 | 82.4 | 93.7 | 108.7 | 115.6 | 120.8 | 124.8 | 128.3 4 | 85.6 | 97.0 | 112.0 | 118.9 | 124.0 | 128.1 | 131.5 5 | 87.6 | 99.3 | 114.4 | 121.3 | 126.5 | 130.6 | 134.1 6 | 89.1 | 101.0 | 116.3 | 123.2 | 128.6 | 132.6 | 136.3 7 | 90.0 | 102.4 | 118.0 | 125.0 | 130.4 | 134.6 | 138.2 8 | 90.0 | 103.3 | 119.3 | 126.4 | 132.0 | 136.3 | 140.0 9 | 90.7 | 104.0 | 120.4 | 127.7 | 133.3 | 137.7 | 141.6 10 | 90.8 | 104.5 | 121.4 | 128.8 | 134.5 | 139.0 | 142.9 11 | 90.9 | 104.7 | 122.0 | 129.7 | 135.6 | 140.2 | 144.2 12 | 91.0 | 104.8 | 122.5 | 130.4 | 136.4 | 141.1 | 145.2 13 | 91.0 | 105.0 | 122.9 | 131.0 | 137.1 | 141.9 | 146.1 14 | 91.0 | 105.0 | 123.2 | 131.5 | 137.6 | 142.5 | 146.7 15 | 91.0 | 105.0 | 123.6 | 131.8 | 138.0 | 142.9 | 147.2 20(?)| | | 123.9 | 132.9 | | |