The invention 2 further comprising control means for accurately setting, conveniently adjusting and immediately releasing the fluid pressure applied to said piston, said means comprising a fluid pressure control device attached to the trenching apparatus for regulating {HEAD ~ the fluid pressure} in said {TAIL ~ piston chamber} and a release value attached to the trencher for relieving the fluid pressure in said piston chamber 
The invention 2 further comprising control means for accurately setting , conveniently adjusting and immediately releasing the fluid pressure applied to said piston , said means comprising a fluid pressure control device attached to the trenching apparatus for regulating { HEAD ~ the fluid pressure } in said { TAIL ~ piston chamber } and a release value attached to the trencher for relieving the fluid pressure in said piston chamber
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