PART I. FLOW IN PRESSURE PIPES. 
FORMULAS FOR FLOW OF WATER IN CONCRETE PRESSURE PIPE. 
Water is caused to flow and velocity created by the force of gravity. 
Thus the flow follows the general law of falling bodies, and the velocity 
tends to become constantly accelerated. This tendency is just bal- 
anced by the influences retarding the flow. 
For a pipe carrying flowing water under pressure, the difference in 
elevation H E (fig. 1), between the surfaces of the water at the intake 
and outlet is the effective head through which the force of gravity 
acts. The effective or lost head is made up of several individual 
losses as follows (fig. 1): 
V 2 
Velocity head = Ji v = -x~ (1) 
This is the head absorbed in creating the mean velocity V, at which 
the water is conveyed through the pipe. This loss occurs at the 
Elevat/on £ 
//C 9 r *Je /^^i*4;B4 
Dai urn--' 
Fig. 1. — Hydraulic elements for loss of head in siphon pipe. 
intake. As a rule, little or none of this velocity head is recov- 
ered at the outlet of the pipe. 
Entry head, Ji e = 7^ (approximately) 
(2) 
The amount of loss at the entry, due to the effect of contraction 
eddies and other retarding influences, is variable and uncertain, but 
most authorities agree that it should be taken as half the velocity head, 
unless the inlet structure is especially designed to minimize this loss. 
For further discussion see page 52. 
Friction head, Ji f , is that lost in overcoming the retarding influences 
within a reasonably straight pipe. In pipes of great length, the 
amount of this loss so far exceeds the two losses first mentioned that 
they often may be neglected, especially in small pipes. This is the 
loss upon which the experiments described in this paper were con- 
centrated. 
5 
