▁one ▁direction ▁from ▁supply ▁to ▁dis charge . ▁When ▁the ▁boost er ▁is ▁in active , ▁and ▁the ▁p ist on ▁is ▁station ary , ▁gas ▁will ▁flow ▁from ▁the ▁in let ▁h ose , ▁through ▁the ▁in let ▁val ve ▁into ▁the ▁space ▁between ▁the ▁cyl inder ▁head ▁and ▁the ▁p ist on . ▁If ▁the ▁pressure ▁in ▁the ▁out let ▁h ose ▁is ▁lower , ▁it ▁will ▁then ▁flow ▁out ▁and ▁to ▁whatever ▁the ▁out let ▁h ose ▁is ▁connected ▁to . ▁This ▁flow ▁will ▁stop ▁when ▁the ▁pressure ▁is ▁equal ized , ▁taking ▁val ve ▁opening ▁press ures ▁into ▁account . ▁ ▁Once ▁the ▁flow ▁has ▁stopped , ▁the ▁boost er ▁is ▁started , ▁and ▁as ▁the ▁p ist on ▁withdraw s ▁along ▁the ▁cyl inder , ▁increasing ▁the ▁volume ▁between ▁the ▁cyl inder ▁head ▁and ▁the ▁p ist on ▁crown , ▁the ▁pressure ▁in ▁the ▁cyl inder ▁will ▁drop , ▁and ▁gas ▁will ▁flow ▁in ▁from ▁the ▁in let ▁port . ▁On ▁the ▁return ▁cycle , ▁the ▁p ist on ▁moves ▁toward ▁the ▁cyl inder ▁head , ▁decre asing ▁the ▁volume ▁of ▁the ▁space ▁and ▁compress ing ▁the ▁gas ▁until ▁the ▁pressure ▁is ▁sufficient ▁to ▁overcome ▁the ▁pressure ▁in ▁the ▁out let ▁line ▁and ▁the ▁opening ▁pressure ▁of ▁the ▁out let ▁val ve . ▁At ▁that ▁point , ▁the ▁gas ▁will ▁flow ▁out ▁of ▁the ▁cyl inder ▁via ▁the ▁out let ▁val ve ▁and ▁port . ▁▁ ▁There ▁will ▁always ▁be ▁some ▁com pressed ▁gas ▁remaining ▁in ▁the ▁cyl