52 
BULLETIN 852, IT. S. DEPARTVCEXT OE AGRICULTURE. 
approaches the pipe outlet at a velocity relatively high compared 
with the velocity in the open water below the outlet chamber. This 
total may be expressed by the formula 
H e = Ji v ^Ji € -]-}o f -Ji , v (20) 
where H e has the significance shown in figure 1 and Ji v , Ji e , and ~h f , 
and T\ v ' have the significance defined on page 51. The influence of 
gentle curves was included in the data upon which the formulas 
were based, so that an additional loss for slight bends or curves need 
not be considered in the design of the usual pipe on irrigation systems, 
If sharp bends can not be avoided, then an additional loss of head 
must be anticipated. The results of such tests as have been made 
on bends in pipes are given in standard works on hydraulics. 
VELOCITY AND ENTRY LOSSES. 
In designing pipes of small diameter and great length, the losses 
due to velocity and entry heads, Ti v and ~h c , are so small compared 
with the friction loss that they may be neglected. Otherwise they 
should be included in the allowance for total lost head. 
It is best to consider the water above any intake as at rest. From 
this state of rest velocity must be created and increased to the mean 
velocity, V, existing in the pipe. The head, Ji v , necessary to create a 
given velocity is shown in column 2, Table 5. The entry loss will be 
from 0.5 Ti v where the pipe of standard size begins at a headwall and 
is without bell or taper mouth, to about 0.25 Ti n for a rounded intake, 
and 0.05 ~h v for a bell-mouth intake. In Table 5, column 3, is 
shown the amount of entry loss when taken as half the velocity 
head (column 2), and the sum of the entry and velocity losses is 
shown in column 4. 
Table 5. — Mean velocity in pipe V, in feet per second, and head of elevation lost creating 
this velocity and overcoming entrance conditions, h v and h t . in feet. 
1 
2 
3 
4 
1 
2 
3 
4 
V 
Tiv 
he 
hv+he 
V 
ht, 
h e 
hv+T, e 
Ft 
per sec. 
Feet. 
Feet. 
Feet. 
Ft. per sec. 
Feet. 
Feet. 
Feet. 
1.0 
0.016 
0.008 
0.024 
5.0 
0.3S9 
0.195 
0.584 
.2 
.022 
.011 
.033 
.2 
.420 
.210 
.630 
.4 
.030 
. 015' 
.045 
.4 
. 453 
.227 
-680 
.6 
.040 
.020 
.060 
.6 
.488 
.244 
.732 
.8 
.050 
.025 
.075 
.8 
.523 
.262 
.7S5 
2.0 
.062 
.031 
.093 
6.0 
.560 
.280 
.840 
.2 
.075 
.037 
.112 
.2 
.598 
.299 
.897 
.4 
.090 
.045 
.135 
.4 
.637 
.319 
.956 
.6 
.105 
. 053 
.158 
.6 
.677 
.339 
1.016 
.8 
.122 
.061 
.183 
.8 
.719 
.359 
1.078 
3.0 
.140 
.070 
.210 
7.0 
.762 
.381 
1.143 
.2 
.159 
.080 
.239 
.2 
.806 
.403 
1.209 
.4 
.ISO 
.090 
.270 
.4 
.851 
.426 
1.277 
.6 
.202 
.101 
.303 
.6 
.898 
.449 
1.347 
.8 
.224 
.112 
.336 
.8 
.946 
.473 
1.419 
4.0 
.249 
.125 
.374 
8.0 
.995 
.498 
1.493 
• .2 
.274 
.137 
.411 
.2 
1.045 
.523 
1.568 
.4 
.301 
.151 
.452 
.4 
1.097 
.549 
1.646 
.6 
.329 
.165 
.494 
.6 
1.150 
.575 
1-725 
.8 
.358 
.179 
.537 
.8 
1.204 
.602 
1.806 
