▁with ▁the ▁com pressed ▁air . ▁ ▁The ▁tool ▁works ▁in ▁a ▁way ▁very ▁similar ▁to ▁a ▁jack ▁ham mer , ▁inside ▁the ▁cyl inder ▁is ▁a ▁p ist on ▁a ▁val ve ▁opens ▁and ▁the ▁air ▁blow s ▁into ▁the ▁chamber ▁forcing ▁the ▁p ist on ▁forward ▁which ▁in ▁turn ▁prop els ▁the ▁tool ▁forward . ▁ ▁The ▁val ve ▁then ▁sh uts ▁and ▁the ▁p ist on ▁is ▁pushed ▁at ▁a ▁slower ▁speed ▁back ▁in ▁the ▁tool , ▁the ▁val ve ▁re opens ▁the ▁p ist on ▁pounds ▁again ▁and ▁the ▁tools ▁moves ▁forward . ▁ ▁This ▁process ▁is ▁contin ually ▁repeated ▁until ▁the ▁bore ▁has ▁run ▁the ▁intended ▁distance . ▁ ▁Both ▁the ▁l ighter ▁reverse ▁hit ▁of ▁the ▁p ist on ▁and ▁the ▁fr iction ▁of ▁the ▁ground ▁surrounding ▁the ▁tool ▁keep ▁it ▁moving ▁forward ▁instead ▁of ▁stopping . ▁ ▁The ▁speed ▁of ▁the ▁tool ▁can ▁be ▁controlled ▁by ▁a ▁val ve ▁that ▁connect s ▁the ▁tools ▁h ose ▁to ▁the ▁air ▁supply ▁this ▁val ve ▁is ▁outside ▁the ▁tool ▁and ▁remains ▁accessible ▁to ▁the ▁operator . ▁ ▁As ▁the ▁tool ▁pounds ▁through ▁the ▁ground ▁it ▁compress es ▁the ▁soil . ▁This ▁comp action ▁maintain s ▁the ▁same ▁diameter ▁as ▁the ▁tool ▁and ▁leaves ▁the ▁bore ▁hole ▁through ▁which ▁the ▁product ▁is ▁passed . ▁ ▁Perform ing ▁a ▁bore ▁The ▁purpose ▁of ▁the ▁bore ▁is ▁to ▁get ▁from ▁point ▁A ▁to ▁point ▁B ▁under ▁the ▁obst ruction . ▁ ▁First ▁the ▁operator ▁surve ys ▁the ▁area ▁and ▁the ▁obst