The beam pumpjack has become the icon of the oil industry. Known by its whimsical yet descriptive European moniker, the “Nodding Donkey,” beam pumps appear in nearly every story or video clip relating to the oil field. Elegant in their simplicity, they seem to tirelessly perform their jobs, doing their slow and stately bows and curtsies like dancers in a Civil War era cotillion. But perhaps their days are numbered.

Compact design straddles blowout preventers and bolts directly atop wellhead.



A new, highly engineered pumpjack competitor is on the horizon. Called the linear rod pump (LRP), it offers several significant advantages. In the first place, it is only a substitute for the surface pumpjack — the polished rods, stuffing box, connecting rods, and downhole pump barrels remain the same. It can even handle wells that use Corod or Fiberglas sucker rods. This means that it can be installed on a new well or as a replacement on an old well with equal ease.

If it looks like a duck …

The biggest difference between LRPs and conventional pumpjacks is their appearance. Tall and slender, with no obvious moving parts, LRPs blend into the countryside and are scarcely visible from a distance, compared to beam pumping units of similar capacity.

They attach directly to the wellhead and do not require a large concrete level pad. As a result, installation is fast and economical; no site preparation is required; and when interventions or workovers are necessary, there’s no large cumbersome machinery in the way of the pulling unit or coiled tubing equipment. The entire pumping unit and power supply can be transported to the wellsite in a pickup truck. It can be installed in a couple of hours by two workers using a small cherry-picker crane or a gin-pole truck. In fact, the units are so portable they can be easily transported from well to well for temporary production tests or to prove reserves.

Looks aren’t everything

Besides its good looks, the LRP offers several performance advantages over traditional approaches. The pump is both economical and efficient. Lacking the high inertia mechanics of cumbersome systems, a larger percentage of its power is directed at actually lifting the well fluid instead of turning massive gears and counterweights together with the apparatus linkages. At the heart of the system is a rack and pinion gear assembly driven by a highly efficient electrical induction motor and reduction gearbox. A conventional rod clamp is located at the top of the rack, and the polished rod is connected there. Optional air balance cylinders cushion the downstroke and smooth the transition to the upstoke as well as act as a pneumatic counterbalance and lift booster for each upstroke. An oil bath continuously lubricates the polished rod as well as the rack and pinion gears.

The unit’s small footprint is no larger than the wellhead on which it is installed. (Images courtesy of Unico Inc.)



Efficient operation is achieved because the unit’s low inertia and smooth transition from rotational to linear motion requires much less horsepower than a beam pumpjack of similar capacity. The key is in the marriage of the LRP mechanical unit with its electrical drive and controller.

Four drives in one box provide versatility

Depending on operational requirements, an easily configurable pump control is available. Operators can choose a simple standalone system, or they can choose a variety of upgrade packages that add capabilities. These include the motor starter package, the soft-start package, and the flexible variable speed drive package. All of these options can be enhanced by instrument kits such as load cells or inclinometers, etc., that can be used to monitor pumping unit performance.

Briefly, the versatile pump controller (VPC) options address the following applications:
• Standalone — provides a simple pump-off control for use with a separate motor control package, as one might use to control a different type pump;
• Motor starter — adds an incoming circuit breaker and a motor-starter contactor in a single box;
• Soft start — uses a solid-state motor starter that extends equipment life by eliminating torque oscillations and electrical current surges during start-up; and
• Variable speed drive — uses a variable-speed drive (VSD) with patented sucker rod pumping control software to continuously optimize well production and pump performance.

The benefits of coupling a mechanically efficient pumping unit with a versatile electrical controller are many. Principle among these is the ability to optimize both pump system performance and well production performance. This translates into longer equipment life as well as lower electrical bills while draining the reservoir at its most efficient rate. The LRP system takes advantage of the motor-reversing and servo-positioning features of a flux-vector VSD to directly control the rack and pinion mechanism. In case of rod breakage, the drive system immediately shuts down so no damage is suffered by the LRP. If so equipped, a rod-breakage warning signal is transmitted immediately to the field office so downtime is minimized.

When used for gas-well dewatering, the pump senses and reacts to pump-off conditions and shuts itself down before any damage can occur. Knowing the sump backfill rate, the pump can be automatically recycled on after an appropriate interval so the desired average hydraulic head is maintained at optimal conditions.
The controller can be equipped with any telemetry from land line, wireless telephone, radio, or satellite so critical real-time data can be monitored and controlled remotely from anyplace in the world. This takes advantage of the software’s monitoring and reporting features, whereby entire enterprise production management can be conducted with minimal effort using management-by-exception principles.

Widely configurable system addresses all situations

LRPs can be programmed to run from as slow as 0.5 strokes/min up to 20 strokes/min. Rod stroke can vary from 32 in. to 86 in. Lifting force ranges from 4,000 lb to 40,000 lb.

Perhaps the most advanced feature of the system is its ability to achieve optimal motion profiles, matching surface and downhole dynamometer plots that reflect ideal conditions. This capability is not possible with mechanical pumpjack systems. With this capability, both pump and well performance can be optimized.

Pump fill is automatically regulated by independently adjusting the downstroke and upstroke speeds. A “soft landing” feature eliminates water-hammer, and an automatic valve check detects both standing and traveling valve leakage. The former addresses one of the principle causes of rod or pump failure, and the latter addresses one of the main impediments to pump performance. Because the position of the rack gear is always known, the upper and lower position of the rods’ stroke can be adjusted independently. This feature is not available with purely mechanical systems.

LRPs are not for every well

There are numerous artificial lift solutions, from rod pumps to plunger-lift systems to gas lift to progressive cavity pumps and electrical submersible pumps. Each method has its optimal applications, but for rod-pumped wells, the slim, unobtrusive, economical, and versatile LRP offers clear advantages.