the apparatus starting with the apparatus in retracted condition as shown in the drawings increased pressure in passage 56 causes ball valve 30 to be closed and causes sleeves 24 and 72 to be moved downwardly pin 95 being moved from position a in barrel cam groove 98 to position b in the groove the lands of sleeve 72 moving beneath the lands of the stabilizer blades forces the stabilizer blades out to their expanded positions shown in fig4 when pressure in passage 56 is sufficiently reduced valve 30 opens and spring 61 forces sleeves 24 and 72 up and pin 95 moves to position c of groove 98 wherein the blades remain expanded because sleeve 72 is not moved far enough upwardly to move lands 72 79 off of lands 84a 84b 84c when pressure in passage 56 is again increased valve 30 again closes and sleeves 24 72 are moved down pin 95 moving to position d in groove 98 the blades remaining expanded on the next reduction in passage 56 pressure pin 95 moves to position e of groove 98 and sleeves 24 and 72 move fully up the blades 66 69 being retracted further alternate increases and decreases in drill string pressure in passage 56 moves pin 95 serially to positions f l of groove 98 etc the pin traverse along groove 98 being repeated cyclically for repeated operations of the.