Retainer nut locking apparatus and methods

A method of operating a fluid end, comprising:

• installing a retainer nut assembly on a fluid end body by turning a retainer nut having a threaded outer surface in an installation direction and into a bore formed in the fluid end body, the retainer nut comprising:
• a first surface at a first end of the retainer nut that faces away from the fluid end body,
• a second surface at a second end of the retainer nut that faces the fluid end body, the threaded outer surface disposed between the first surface and the second surface
• a recess formed in the second surface that defines a recessed surface,
• a first opening extending from the first surface to the recessed surface,
• a second opening formed in the recessed surface;
• and
• turning an actuator disposed at least partially in the first opening to rotate a locking tab of a locking assembly from out of contact with a stop of the locking assembly in a locking direction and into contact with an inner surface of the fluid end body, the locking direction being opposite of the installation direction, the stop disposed at least partially in the second opening and protruding from the recessed surface, the actuator configured to rotate the locking tab between an unlocked position and a locked position, and the locking tab disposed inside the bore and adjacent to the second surface of the retainer nut.

A fluid end, comprising:

• a fluid end body;
• a plunger disposed at least partially in the fluid end body;
• a bore defining an inner surface of the fluid end body, the inner surface comprising a threaded portion and a thread relief disposed inward of the threaded portion;
• and
• a retainer nut assembly, the retainer nut assembly comprising:
• a retainer nut disposed at least partially in the bore, the retainer nut comprising:
• a first surface at a first end of the retainer nut,
• a second surface at a second end of the retainer nut,
• a recess formed in the second surface that defines a recessed surface,
• a first opening extending from the first surface to the recessed surface,
• a second opening formed in the recessed surface, and
• a threaded outer surface that interfaces with the threaded portion of the inner surface of the fluid end body, the threaded outer surface disposed between the first surface and the second surface;
• and
• a locking assembly, the locking assembly comprising:
• a locking tab that is rotatable between an unlocked position and a locked position, and in the locked position the locking tab contacts the inner surface of the fluid end body at a location inwards of or at the thread relief,
• a stop disposed at least partially in the second opening and protruding from the recessed surface, and
• an actuator disposed at least partially in the first opening that is configured to rotate the locking tab between the unlocked position and the locked position.