A rod pump is the most commonly used pumping device for oil wells. Known for its distinct shape and design, the rod pump features a pumping mechanism that is almost entirely visible from above the ground. The operating portion of this mechanism moves in a rhythmic motion to draw oil from nearby wells. This rhythmic motion and distinct appearance have led to many nicknames for the rod pump, such as pump jack or horsehead pump.
These pumps can be powered using either an electric or gas motor. The motor rotates a shaft, which in turn rotates a pair of jointed support arms. As these arms rotate, they cause the attached “head” or beam to lift and lower in a steady pattern. A counter-weight above the motor helps to balance out the up-and-down motion of the head to maintain its steady pace.
At the head of the rod pump is a rod and plunger mechanism. Each time the head of the pump lowers towards the earth, it drives the plunger deep underground. This increases pressure within the well, which creates displacement forces that draw oil up towards the surface. The oil is collected within the plunger and transferred to storage vessels each time the rod draws back up to ground level.
Rod pumps are found in large numbers on oil fields, but a single unit can also be used at a small well. For example, some homes in the US have rod pumps within the property to collect small oil reserves underground. These pumps are typically owned by energy companies, which in turn pay the homeowner for use of the land. Rod pump mechanisms are also used in automotive engines to draw oil through the operating system.
Compared to many other types of pumps, the rod pump is a relatively simple device. Because it is so simple, it can be operated easily and efficiently by the average oil worker. With the majority of the operating components located above the ground, these pumps are also easy to repair and maintain. Other pump models may require extensive excavation to access components below the ground for repair or maintenance purposes. Despite their simple design, rod pumps can also draw oil effectively from relatively deep areas.
One of the primary disadvantages of the rod pump is the need to adjust its depth, motor speed, or counter-weights over time. While the design of the pump is initially set to a specific depth, the pressure levels in oil wells often change over time as oil is removed, or due to simple seismic shifts. While some more complex pumps can automatically adjust to these changes, a rod pump requires a more hands-on approach to draw oil once conditions change.