64 BULLETIN 376, U. S. DEPARTMENT OF AGRICULTURE. 
the water surface at the intake, gave the loss of head between the 
intake and gauge No. 1. These losses are shown in column 4. 
Column 7 gives the friction loss between a point 3 diameters down 
the pipe from the intake and gauge No. 1. This column is based 
upon the friction loss per foot within the pipe (column 5) multiplied 
by the number of feet (column 6) back from gauge No. 1 to the 
3-diameter point. Column 4 less column 7 gives the computed loss 
of head (column 8) due to velocity and entry heads combined be- 
tween the intake and the 3-diameter point. Theoretically column 8 
should approximate column 11, which is the sum of columns 9 and 
10, but in most cases the velocity of approach was sufficient to make 
the entries in column 8 much smaller than those in column 11. 
Referring to these two columns: Tests 1 and 2 were conducted on 
a concrete pipe where the water entered a 16-inch standpipe from an 
8-inch pipe and left the opposite side in an 8-inch pipe. The obser- 
vations show that no head was lost within the standpipe. Tests 3 
and 4 were on pipes in an installation similar except that the water 
left the standpipe in a 12-inch pipe at right angles to an 8-inch pipe 
through which it entered. Tests 5 and 6 were on the pipe shown in 
Plate XII, figure 3. Here the velocity of approach in the canal 
acted directly on the intake opening, greatly reducing the loss of 
head. Tests 7 and 8 were on a similar pipe, but in this instance the 
canal turned an abrupt right angle just before entering the pipe, 
causing a violently turbulent condition which probably introduced a 
large error in the observed head at the intake. 
AIR IN PIPE. 
In speaking of a pipe that did not show sufficient carrying capacity 
Moritz states : * 
Examination showed that air imprisoned in the pipe was causing the difficulty. 
This was overcome by inserting a J-inch wrought-iron standpipe in the top of the pipe 
about 15 feet below the intake. In this way the air was, to all appearances, entirely 
removed, and the carrying capacity was raised to 1.54 cubic feet per second, an 
increase of about 60 per cent. 
Pipes taking water directly from reservoirs are, of course, not sub- 
ject to these troubles, the depth above the intake being, as a rule, 
sufficient to insure filling of the pipe with water alone. 
Siphon pipes and, in even greater degree, pipe chutes are often 
reduced in carrying capacity by entrained air. In his investigations 
on wood-stave pipes the writer has observed that air troubles are 
minimized under the following conditions: (a) Low velocity in 
channel approaching inlet; (b) inlet end set well below the hy- 
draulic gradient, as a rule with top of pipe at about same elevation 
as bottom of the canal above the inlet; (c) intake chamber designed 
to minimize eddies. 
i Trans. Amer. Soc. Civ. Engin., 74 (1911), p. 435. 
