Reciprocating pump with fluid end

A retainer of a fluid end, the retainer comprising:

• a threaded portion configured to engage with threads of a wall of the fluid end, the wall defining a bore in which the retainer is configured to be inserted, the threaded portion extending from an interior surface to a shoulder of the retainer, and the interior surface is configured to lead insertion of the retainer into the bore;
• and
• an unthreaded portion extending from the shoulder to an exterior surface, opposite the interior surface, to establish a center of gravity of the retainer, wherein a first distance between the center of gravity and the exterior surface is within 10% of a second distance between the center of gravity and the interior surface to provide sufficient rigidity of the retainer to withstand rotation relative to the wall of the fluid end while the threaded portion is engaged with the threads of the wall.

A fluid end of a reciprocating pump, the fluid end comprising:

• a housing having a bore extending along an axis from a pumping chamber of the housing to an external surface of the housing, the bore comprising a wall with threads configured to engage a retainer installed in the bore, wherein the wall comprises a first diameter and extends a length along the axis;
• and
• a reciprocating element extending along the axis and comprising a second diameter, wherein the length of the wall in centimeters plus a ratio of the first diameter of the wall in centimeters relative to the second diameter of the reciprocating element in centimeters is greater than 10.31.