Abstract: The present invention provides in one aspect a braking mechanism for slowing the release of torsional potential energy in a rod string of a wellhead drive system on the shutdown or power failure thereof. The braking mechanism, without using a slip clutch, slows the backspin of the rod string by using the rotational energy of the rod string to turn a fluid pump to pump fluid through a constriction orifice in a closed fluid circuit. The present invention reduces the space required for the braking mechanism and moreover reduces the number of moving parts within the braking mechanism which may reduce the likelihood that the braking mechanism will require maintenance or fail, as well as reduce the manufacturing cost. In another aspect, the present invention provides a wellhead drive system for driving a rotary downhole pump which includes the inventive braking mechanism described above.

Abstract: A braking mechanism, for controlling the release of energy in a rod string (34) for a down-well rotary pump (33), incorporates a rotary member (16) positioned in the energy loop from a prime mover to the top end of the rod string, requiring that the rotary member rotate at a consistent speed ratio and direction with respect to the top end of the rod string. The rotary member drives a fluid pump through a slip clutch so that when the top end of the string rotates in the normal direction, the clutch slips and does not run the fluid pump. However when the top end of the rod string seeks to rotate in the opposite direction, for example on shut-down or power failure, the fluid pump is operated to pump fluid from a reservoir (20) and back to the reservoir in a closed loop which includes a mechanism for restricting fluid flow.

Abstract: An assembly for restraining oil leakage in a rotary oil well pump includes a stationary member and a rotary member. The rotary member is secured to the rotating rod and is sealed against the rod by conventional compressed packing. The rotary member has a cylindrical portion rotating within a cylindrical recess of the stationary member, with an annular recess defined between them. The recess contains two or more annular seal cartridges stacked one after the other in the annular space. The cartridges are designed to individually resist the ingress of the pressurized oil, so that leakage takes place sequentially past the individual cartridges. Leak passages are provided in the stationary member and are in communication with each of the cartridges respectively. When oil appears at any given leak passage, this signifies that the oil has bridged the defences of that cartridge and any cartridge or cartridges which are upstream of the leaking cartridge.