radial ports 73 sealing unit 21 disengages from the inside of valve mandrel 40 exposing radial ports 72 to the inside of valve housing 17 as shown in fig3 a relatively high pressure chamber 60 defined by o ring 46 and sealing unit 25 is open to work string 96 by ports 24 26 27 and 93 see fig6 pressure in chamber 60 applies a force on valve sleeve 16 in the downward direction to further push knife sub 18 into engagement with knife seal 70 with return spring 20 in a generally compressed condition it generates a force on steel balls 36 radially inward onto plunger 80 sufficient to hold the plunger in the position shown in fig3 in this position steel balls 36 prevent piston 29 from moving upward and lock flow control valve 10 in the injecting position thus delivery of pressurized fluid from the work string 96 through the plunger 80 the aligned radial ports 72 73 and the axial ports 35 in the valve housing 17 is cut off when the piston 19 is moved downwardly allowing the balls 36 to move outwardly into the annular recesses 65 in the piston thus freeing the plunger 80 to move downwardly and cut off communication between the radial ports 72 and 73 as explained such downwards movement of the piston 29 is in response to the differential pressure which acts thereacross namely the downwards force generated by pressure in the chamber 57 acting on the upper end of the piston 29 less the.