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and the traveling valve. On the upstroke part of pumping cycle the
fluid load on the plunger causes the traveling valve to close, and
fluid is displaced from the tubing at the surface. Also the motion of
the plunger causes a pressure decrease above the standing valve
which opens and admits fluid from the formation. At the beginning
of the downstroke the plunger begins to fall through the fluid in
the tubing. Consequently, the traveling valve opens, the standing
valve closes, and the fluid load is transferred from the plunger to
the tubing. This transfer of fluid load is a significant factor in
determining the effective plunger stroke. It should be noted that
most of the production is accomplished on the upstroke, the only
fluid removed from the tubing during the downstroke being that
which is displaced by the falling rods.

Figure 20.1 - Sucker rod pumping unit

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