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The walking beam is supported near its center of gravity by
the sampson post. Motion is transmitted to the walking beam by
the pitman, to which motion is in turn transmitted by the crank.
The distance from the crank shaft to the pitman bearing defines the
polished rod stroke length. Most units have three or more possible
locations for the pitman bearing along the crank and, therefore, a
corresponding number of possible stroke lengths. One of the most
important aspects of pumping installation design is per selection of
counterbalance. Practically all of the work of lifting fluid by a
sucker rod pump is performed during the upstroke part of the
pumping cycle. During this phase of the cycle, the full load of oil
and sucker rods must be accelerated upward from zero velocity,
and must be lifted the length of the pump stroke. On the
downstroke, with fluid load transferred to the tubing, the falling
rods act as a driving force for the installation. If some means
were not provided for equalizing these upstroke and downstroke
loads, conditions detrimental to the surface pumping equipment
would result. From the standpoint of the prime mover,
unnecessarily high demand for power would occur during the
upstroke, with the prime mover driven during the downstroke.
(This would cause the prime mover speed to be greater on the
downstroke than on the upstroke.). From the Standpoint of power
transmission, unnecessarily high torque would be imposed during
the upstroke. Counterbalancing provides for even distribution of
loads and for reduction of peak torque requirements. The counter-
balance weights, in effect, store energy during the downstroke
when power demand is low, and release energy during the
upstroke, performing part of the work of lifting fluid and rods.
To avoid a possible misinterpretation of terminology, it is
necessary to differentiate between counterbalance effect (which is
the net contribution to the counterbalance system at the polished
rod) and counterbalance or counterweight (which is the weight or
system of weights used to obtain the counterbalance effect). The
counterbalance effect is determined by the actual weight of the

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