Once Vulcan got past designs such as this, the slide bar (the cam which turned the valve during operation) was retained in a ram using a key driven though the base of the slide bar. The slide bar interfaced with the ram using a spherical block to allow rotation of the bar, necessary to compensate for alignment changes. This worked until the advent of nylon slide bars, which became de rigeur for offshore hammer during the 1960’s and onshore a little while later. These were more prone to split with driving the key.
The problem was solved by moving the key under the slide bar and using a gripper to hold the slide bar to the key interface. It was invented by Campbell V. Adams, Vulcan’s long time chief engineer, and he was granted a patent on it in 1967 (it was Adams’ last patent for Vulcan.)