Significant here is that the entire operation by which the friction discs and reaction plates are released, forward motion of the trencher stopped, {HEAD ~ the trencher} moved backwards so as to clear the obstruction, {TAIL ~ the wheel} restarted, and the trencher again placed in forward motion, are all accomplished without the operator having to move the crowd handles, or readjust the ultimate setting of the piston pressure 
Significant here is that the entire operation by which the friction discs and reaction plates are released , forward motion of the trencher stopped , { HEAD ~ the trencher } moved backwards so as to clear the obstruction , { TAIL ~ the wheel } restarted , and the trencher again placed in forward motion , are all accomplished without the operator having to move the crowd handles , or readjust the ultimate setting of the piston pressure
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