Piston retention apparatus and method

A piston and rod assembly for use with an actuating device, comprising:

• a piston member having a piston bore extending between a first end and a second end, the piston bore having a threaded segment;
• a rod member having a first threaded region threadably engaged with the threaded segment, an end region extending beyond the second end of the piston member, where the end region comprises a second threaded region;
• and
• a retaining member having a retaining bore extending therein, the retaining bore having a threaded portion threadably engaged with the second threaded region,
• wherein an external thread of each of the threaded segment and the first threaded region has a pitch and is formed with a root radius in the range of about 0.15 pitch to about 0.18 pitch, wherein the piston bore comprises an inner seat and the rod member comprises an outer shoulder, the inner seat and the outer shoulder engage one another to form an interface, the piston bore comprises an inner seal groove disposed adjacent the inner seat to include a seal member, the interface and the inner seal groove disposed closer to the first end of the piston member than the threaded segment.

A method of coupling a piston member having a piston bore with a rod member, comprising:

• threadably engaging a first portion of the rod member with the piston bore at a torque until an inner seat of the piston bore and an outer shoulder of the rod member engage with one another, wherein an external thread of each of a threaded segment of the piston bore and a first threaded region of the first portion of the rod member has a pitch and is formed with a root radius of greater than 0.125 pitch;
• threadably engaging a second portion of the rod member into a retaining bore of a retaining member;
• and
• threadably engaging at least one setscrew through a corresponding setscrew bore formed in the retaining member so that a tip of the setscrew engages the rod member.