CKANE VALVES 



761 



The valve stem // is raised by a cam surface cut in the upper side of 

 , rock-shaft G. The stem does not directly open the main valve ; the 

 upper end of a stem passes through main valve L in a clearance hole as 

 shown, and when raised, it strikes against the bottom of pilot valve 

 K, which it lifts against the pressure of the spring above and against 

 the pressure of the water in chamber B. Chamber B is filled with water 

 leaking from inlet space A , past the easy fit of the piston portion of valve L. 

 As soon as K is raised, the pressure in B drops to that in service 



Sectional Elevation. 

 FIG. 375. Slide Valve for Heavy Hydraulic Machinery. 



connection D, since the outlet through the centre of the main valve is 

 much larger than the area through which the leakage escapes from A. 

 Under these circumstances there is an unbalanced pressure on valve L 

 from the water in A, which forces it from its seat on ring C, this 

 unbalanced pressure being due to the fact that the piston portion of main 

 valve L is much larger in diameter than the seat on which it rests 

 in ring C. 



In closing, the reverse of this action takes place. Handle F being 

 brought back to its central position, valve stem H, and with it pilot valve 

 K, are lowered until the latter reaches its seat in valve L. Connection 



