792 HYDRAULICS AND ITS APPLICATIONS 



The solution of this equation is 



c ~ bx 



F 2 = r + D e where D is a constant, 



Putting V = Vi when x = we have Fi 2 = - -f- 7>, 



giving the velocity after a piston displacement x foot. 

 This may be written 



or x = 



bx 



e = 



c 



J,'2 C 



6 



b 2-302 



feet. 



y<2 C 



b 



giving the position of the piston when the velocity has been reduced from 

 FI to V feet per second. 



Fig. 398 indicates the variation of pressure intensity inside the cylinder 

 with piston displacement in the cases (a) where the resistance is uniform ; 

 (b) where a compression buffer without tail rod, having passages of 

 uniform area and with air compression is used ; and (c) with a tension 

 buffer with passages of uniform area. 



With constant pressure and resistance, the maximum pressure attained 

 is about one-third that in the case of the tension buffer with passages of 

 uniform area. 



ART. 210. THE HYDRAULIC DYNAMOMETER 



is certainly the most perfect of all mechanical devices for measuring and 

 absorbing the energy developed by a prime mover at a rotating shaft. 



In its modern form it owes its conception in all but one essential to 

 the late Mr. William Froude ; but the addition of the one detail which 

 made the brake a practical success was due to Professor Osborne 

 Reynolds. 



The Reynolds or Mather-Reynolds Dynamometer shown in Fig. 399 

 consists of a double disc D, fixed to the power shaft by set screws or 

 keys and carrying on its outer faces a series of narrow pockets. 



These latter are semicircular in section, their plane is inclined at 45 

 to the axis of the shaft, and they face forwards in the direction of motion. 



