(02) THE MEASUREMENT OF DOWN STROKE FORCE IN ROD PUMPS
During the down stroke the plunger in a rod pump must fall through a barrel that is filled with fluid. The plunger will establish a free fall velocity that is determined by the forces resisting downward motion. The free fall of the plunger may not be large enough to correspond to the actual velocity necessary to match the pumping speed set by the pumping unit. In this case the plunger must be pushed into the barrel by a compressive force in order to match the pumping velocity. The compressive force may be large enough to cause buckling in the lowest section of sucker rods. The purpose of this paper is to test this hypothesis by presenting measurements of the free fall velocity of a plunger in a liquid filled barrel and the pushing force necessary to exceed the free fall velocity of the plunger in the barrel. Simple models are shown to relate the measurments to practice.