LOSSES AT BENDS 

 indicated in the following table : 



251 



This loss due to alteration in area and shape of section is serious in 

 all hydraulic machinery when working at high velocities, and especially 

 in machines of the piston type, Here, for efficiency of working, it is 



FIG. 113. 



above all things important that the velocities should be kept as low as 

 possible. 



(4) Losses at Bends and Elbows. Whenever the direction of motion of 

 a stream is abruptly changed, as at a sharp bend or elbow, a loss of head 

 is experienced which appears to be due to the formation of a vena con- 

 tracta 011 passing the elbow and to the subsequent re-enlargement and 

 shock which then takes place (Fig. 113). With an easy bend, recent 

 experiments 1 by Dr. Brightmore show that the state of affairs is very 

 different, the water flowing round the bend with a motion approxi- 

 mating to that in a free vortex, its velocity being greatest at the inside 

 and least at the outside of the bend. In these experiments it was 

 shown that in such a case the loss due to the bend does not occur so 



1 " Proceedings Institute Civil Engineers," 1906-7, vol. 169, p. 315. 



