Patent Number: 050251589
Section: claims

1. A stepping apparatus for advancing a hydroball detector string having a plurality of spaced apart balls on a cable and being movable in a direction of a counter through a tube under fluid pressure, comprising: first and second gate means operably coupled to the tube upstream of the counter, for blocking movement of the spring without blocking fluid flow through the tube; and  actuator means for moving the first and second gate means in steps into and out of blocking positions in the tube to thereby advance the string one ball at a time to the counter.  (a) blocking a first ball of the detector string by abutment with a first gate movable into a blocking position in the tube;  (b) moving a second gate between an adjacent ball and the first ball into a blocking position within the tube;  (c) withdrawing the first gate from a blocking position, whereby fluid pressure advances the detector string towards the counter until the adjacent ball abuts the second gate, thereby completing a first step;  (d) moving the first gate between the first ball and the adjacent ball; and  (e) withdrawing the second gate from a blocking position, whereby fluid pressure advances the detector string towards the counter until the adjacent ball abuts the first gate, thereby completing a second step. 2. A stepping apparatus as recited in claim 1, wherein each of the first and second gate means comprises a gate element movable transversely into the tube. 3. A stepping apparatus as recited in claim 1, further comprising a body member having an axial bore, the opposite ends of which are sealingly coupled to the counter tube, and through which the detector string travels, the first and second gate means being mounted in the body member. 4. A stepping apparatus as recited in claim 3, wherein the body member has first and second transverse bores intersecting the axial bore and slidably receiving the first and second gate members, respectively. 5. A stepping apparatus as recited in claim 4, wherein the actuator means comprises first and second solenoid actuators coupled to the first and second gate members, respectively. 6. A stepping apparatus as recited in claim 5, wherein each of the first and second gate members has a first passage through which balls of the detector string freely pass, and a second passage through which only the cable of the detector string freely passes while providing an abutment against which the balls are blocked. 7. A stepping apparatus as recited in claim 6, further comprising means for stopping the first and second gate members when extended to an open position in which the balls of the detector string freely pass through the first passage of the respective gate member. 8. A stepping apparatus as recited in claim 1, wherein the actuator means comprises first and second solenoid actuators coupled to the first and second gate means, respectively. 9. A stepping apparatus as recited in claim 1, wherein the first and second gate means are spaced apart by a distance corresponding to a distance between two adjacent balls of the detector string. 10. A method of advancing a hydroball detector string having a plurality of spaced apart balls on a cable and being movable in a direction of a counter through a tube under fluid pressure, the method comprising: 11. A method as recited in claim 10, further comprising sequentially repeating steps (b)-(e) to further advance next adjacent balls of the detector string towards the counter. 12. A method as recited in claim 10, wherein the moving steps (b) and (d) and the withdrawing steps (c) and (e) comprise selectively energizing and de-energizing first and second solenoid actuators coupled respectively to the first and second gates.