whereby each of said front and rear face portions draws {HEAD ~ an exterior fluid} into said front gap portions of said front and rear face portions at forwardly directed movements of said piston shoes and into {TAIL ~ said rear gap portions} of said front and rear face portions at rearwardly directed movements of said piston shoes, 
into
whereby each of said front and rear face portions draws { HEAD ~ an exterior fluid } into said front gap portions of said front and rear face portions at forwardly directed movements of said piston shoes and into { TAIL ~ said rear gap portions } of said front and rear face portions at rearwardly directed movements of said piston shoes ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH