fluid pressure in the axial flow passage 24 exceeding the fluid pressure in the annulus external to the apparatus 10 by an amount sufficient to overcome the upwardly biasing force exerted by the spring 92 as shown in fig2 a 2c the mandrel 30 has been axially downwardly displaced relative to the upper slip 56 since the upper slip 56 prevents upward displacement of the mandrel 30 as more fully described hereinabove this downward displacement of the a mandrel 30 may not be reversed thus each time the mandrel 30 is downwardly displaced such displacement is incremental and is added to any prior downward displacement of the mandrel 30 relative to the lower housing 36 the piston 72 lower slip 58 retainer 88 wavy spring 90 and washer 91 may be returned to their positions as shown in fig1 b wherein the piston 72 axially contacts the upper housing 22 by reducing the pressure differential between the axial flow passage 24 and the annulus external to the apparatus 10 when the pressure differential has been reduced sufficiently the upwardly biasing force exerted by spring 92 on the retainer 88 will overcome the downwardly biasing force exerted by the pressure differential acting on the differential piston area between.