How Do Oil Derrick Pumpjacks Work?

For anyone who has ever driven through the southern United States or other oil-rich areas, you likely are familiar with the sight of oil derrick pumps. These metal moving hammer-like structures work to extract oil from underground – often in the middle of nowhere. All this probably leaves you wondering, how do they actually work and what happens to the oil once it’s taken from below ground?

Called pumpjacks, oil horses, oil derrick pumps, these large metal structures are crucial to supplying the US and ultimately the world with its oil needs. They function as traditional sucker rod pumps, known more technically as reciprocating piston pumps, and are made up of 5 parts: the prime mover, the crank, the samson posts, the walking beam, and the sucker rod.

Image Source: Concerning Reality

The samson posts are those that make up the main A frame of the structure. They function as the basic support allowing the pumping mechanisms to work together. Atop the samson posts sits the walking beam attached to a piece called the horse head. These parts together make up the major lever arm in the structure responsible for most of the pumping. These move up and down due to rotational movement from a smaller arm called the crank. The crank usually has a counterweight to balance out the forces on the oil derrick and it gets it’s power from the prime mover, usually through a gearbox.

The prime mover is simply a complicated name for a motor or engine. This supplies the rotational energy to the system that works through all of the subsequent parts to create the bobbing pumping motion these derricks are known for.

But all of that was a complicated preface to how these massive pumps actually work to remove oil from the ground.

Attached to the horse head is something called a sucker rod, which moves up and down in the oil well hole. There are two stages of the pumping process, the upstroke, and the downstroke. Simple enough.

Image Source: Concerning Reality

On the upstroke, the derrick pulls the rod up from the bottom the well to the top of its range of movement. There’s a valve attached to the bottom of the sucker rod known as the riding valve and another at the bottom of the well known as the standing valve. On the upstroke, the riding valve is closed and the standing valve is open, allowing oil from the source to be drawn up into the well. Then, on the downstroke, the riding valve opens and the standing valve closes, putting the oil from that stroke on the other side of the riding valve. Repeating this process over and over again slowly pushing the oil up and out of the well at a rate determined by the pumps speed, size of stroke, and well diameter.

This functionality works similarly to how most pumps work using what would traditionally be called a check valve. This valve functions identically to how the valves in the oil derrick work, allowing flow of a fluid in one direction, but not the other. As the oil horse operates, the oil is forced out of the reservoir and the valves don’t allow it to flow in the other direction.

A look at the cross-section of a check valve. Image Source: Concerning Reality

Their size is usually directly correlated with how deep an oil well might be – the larger the oil horse, the deeper the oil reserve. This relation is simply because bringing oil up from deeper depths requires a significantly larger amount of effort.

These derricks generally pump anywhere from 1.5 to 10 gallons of oil per stroke. The liquid extracted is usually a mixture of crude oil and water that then needs to be separated and refined.

As for what happens to the oil once it is pumped, there are two options. Depending upon location, some derricks will fill a large container with the oil that is then trucked away at certain intervals, or, the oil is directly pumped to a central holding station through a pipeline.

While renewable energies may be making a strong play for powering the world, oil will likely be here to stay for quite some time. All this means that the oil horses across the world will keep on bobbing bringing up oil from deep beneath the surface. And now, when you drive past them on the road, you can understand that these seemingly complex machines are actually just large simple pumps working to help your car keep on moving.

Below, you’ll find some looping GIFS taken from the video in this article to help explain everything as well.

Trevor is a civil engineer by trade and an accomplished internet blogger with a passion for inspiring everyone with new and exciting technologies. He is also a published children’s book author whose most recent book, ZOOM Go the Vehicles, is aimed at inspiring young kids to have an interest in engineering.

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