4 BULLETIISr 376, U. S. DEPARTMENT OF AGEICULTURE. 



m=K d=^. — The equation for the variation in m for a saries of pipes of various sizes 

 but with the same characteristics; K is the intercept on the vertical axis, 

 and X is the slope of the line, when values of m are plotted as ordinates 

 and values of d as abscissse. (See equation 19, p. 49.) 

 m'' — The special values of m found for each series of pipes, by drawing lines from the 

 centers of gravity for the observations in each series, at a constant slope, to an 

 intersection with the vertical axis. 

 No. — . — ^Wherever a pipe number is given, the reference is to the corresponding 

 number in Tables 2 and 3, to Plate VII, ahd to the description of the pipe 

 under that number. 



FORMULAS FOR FLOW OF WATER IN WOOD-STAVE PIPE. 



Water is caused to flow and velocity created by the force of gravity. 

 Thus the flow follows the general law of falHng bodies, and the 

 velocity tends to become constantly accelerated. This tendency is 

 just balanced by the influences retarding the flow. For a pipe carry- 

 ing flowing water under pressure, the difference in elevation, Hj. 



Fig. 1. — Hydraulic elements for loss of head in siphon pipe. 



(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 fol- 

 lows (fig. 1) : 



Y2 



Velocity head = l^v = o^* ( 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 

 intake. 



As a rule, httle or none of this velocity head is recovered at the 

 outlet of the pipe. The conditions under which recovery may be 

 expected are discussed on page 61. 



Entry head, he = -^ (approximately) , 



(2) 



