Abstract: An apparatus for measuring the rate of movement of one object with respect to another, such as a drilling rate recorder used to measure the rate of penetration of a drill bit during drilling operations. One embodiment of the invention includes a frame, a motion imparting means for imparting motion from a drill string; a first arm having one end pivotally mounted on the frame, a second arm pivotally mounted on the first arm, a first cam attached to the motion imparting means and adapted to cause the second arm to pivot about the first arm, and a recording means.

Abstract: A back pressure control choke operates to automatically control and maintain a desired back pressure on the fluid passing through the choke. The choke housing has an inlet channel which intersects with an axial bore, part of which bore constitutes the discharge channel. An annular choke seat concentrically arranged in the discharge channel of the axial bore is adapted to receive an annular choke element. The choke element is affixed to a shuttle which is mounted on a fixed mandrel extending into the axial bore of the choke housing. The shuttle is dynamically sealed against the housing and mandrel such that a closed chamber is created in that portion of the axial bore opposite the discharge channel. The shuttle element is constructed to be fluid balanced such that it will move to achieve an equilibrium of pressure on its forward and rear surfaces.