452 



HYDRAULICS AND ITS APPLICATIONS 



behind the relay piston and forcing the spear rod into the nozzle. This 

 spear rod is connected with the dashpot C, which itself works in the outer 

 fixed casing K, by a series of links and a bell-crank lever not shown in the 

 sketch, and as the spear rod moves to the right the dashpot is lifted, 

 raising at the same time the fulcrum A. During this portion of the 

 motion, there is a slight downward motion of the dashpot plunger and 

 fulcrum relative to the cylinder. As the motion of the latter ceases, how- 

 ever, the plunger is gradually lifted by the weighted lever W, bringing 



FIG. 203. Twin Pelton Wheel with Hydraulic Relay GoverDor. 



down the pin at B, and returning the valve to its central position with the 

 governor lever also in its central position. 



Any further motion of the spear rod is thus stopped until the wheel 

 has had time to readjust itself to the changed conditions, when the whole 

 arrangement is again ready to adjust itself to any fresh change of speed. 



Water ram on closing the nozzle may, if necessary, be prevented by a 

 special automatic device of the makers. In this the spear rod is directly 

 connected through a link with a dashpot plunger, the cylinder of which is 

 vertical, is capable of axial movement, and which is itself connected to a 

 small needle valve which is opened by any upward motion of the 

 cylinder, The. main relief valve is slightly overbalanced hydraulically SQ 



