IMPACT OF JETS 381 



[he effective pressure = 2U? . "CA Ibs. and the work per second 



= ir ^.Cl .!JC ft. Ibs. 



g 



By producing A II to K (Fig. 171 a) and dropping perpendiculars 

 K A', (7 X, on to A H, we can prove that 



~BA 1 - KH* = TT^L (HA + 2 1H). 



Also, since C3 represents the initial relative velocity of jet and vane 

 and ~CH their final relative velocity, we have neglecting friction 



.'. K A + A' // = H A + 2 K II = 2 (7v 77 + // X) 

 .'. HA+2KH = 2KX 



2KX_LM 

 A1S ^WC ~ AH 

 .'. II A (II A + 2 K H) = 2 (L M . J5 C) 



/. Work done = T - F^ 2 - ~ 



where vj and r 2 are the initial and final absolute velocities of the water. 



Work done on vane 



/. Efficiency = rn z =-i --:- per second 



Total energy of ]et r 



Centre of Pressure on Vane. The position of the centre of pressure on 

 any vane receiving a jet tangentially may be determined as follows. 

 Consider any small arc P Q (Fig. 172 a) of the vane. If the velocity is 

 supposed unaltered by friction, P A and A Q, tangents at P and Q 

 represent to some scale the (equal) velocities at P and Q, while E Q, 

 perpendicular to the chord P Q, represents to the same scale the change 

 of velocity between P and (^ Normals P C and Q C to the curve inter- 



sect in (7, the centre of curvature of the arc, and -r-~ TTT^ so ^ na ^ ^ 

 P C represent the velocity v at P, the chord P Q represents the change of 



