PPRL is the maximum upward tensile load experienced at the surface polished rod during the pumping cycle. It combines buoyant rod weight, dynamic acceleration inertia (Mills factor αd), and the net hydrostatic fluid column resting on the traveling valve. PPRL dictates the required structural beam capacity rating of the pumping unit.

Sucker rods undergo millions of cyclic tensile stress reversals annually. The Modified Goodman diagram evaluates maximum operating stress (Smax) against allowable fatigue endurance limit based on minimum stress (Smin), ultimate tensile strength (Su), and environmental service factors (SF): Sallow = [Su/1.75 + 0.362 * Smin] * SF. Exceeding 100% loading causes premature fatigue failure.

Rotating counterweights offset the heavy weight of the sucker rod string and fluid on the upstroke and store energy on the downstroke. Sizing CBE to the ideal average of PPRL and MPRL balances motor load across the full revolution and reduces peak torque on the gearbox reducer teeth by up to 50%.

Fluid pound occurs when low reservoir inflow or high gas volume leaves the pump barrel only partially filled with liquid. On the downstroke, the plunger accelerates through low-density gas before violently slamming into the liquid level at high speed, sending destructive compressive shockwaves up the rod string and rattling gearbox teeth.

A single diameter rod string would experience severe over-stressing near the surface where it must support miles of rod weight below it. Multi-taper strings (e.g. 1" top, 7/8" middle, 3/4" bottom) taper rod diameter downward, distributing stress evenly along the entire string and reducing overall weight and power consumption.