| CPC E21B 7/06 (2013.01) [E21B 17/1014 (2013.01)] | 33 Claims |

|
1. A piston and cylinder assembly of a downhole tool, comprising:
a piston and a cylinder,
the piston having an outer wall which is in direct sliding contact with a wall of the cylinder, the piston being slidable along a cylinder axis, the cylinder having a retainer for the piston, the retainer having at least one retaining part, the piston having at least one retained part, the at least one retaining part and the at least one retained part cooperating to retain the piston in the cylinder, the at least one retained part being separate from the outer wall, in which the at least one retaining part and the at least one retained part are moved into and out of alignment by rotation of the piston around the cylinder axis relative to the cylinder.
|