The pumpjack is probably the component that most readily comes to mind when one thinks of the on-shore oil fields, so I thought it would be interesting to take a closer look at what it does and how it works. The pumpjack is known by many names of which “nodding donkey” and “grasshopper” are but two.
The pump jack is used to extract crude oil from the oil well whenever there is not enough pressure in the well to naturally force the oil to the surface. The pump jack mechanically extracts the oil via a pair of valves in a pump at the bottom of the oil well. These valves alternately open and close in a similar fashion to the piston valves in a car engine.
The long, heavy beam, is called the walking beam and is pivoted on an A frame. It is connected at one end to a power source, such as an electric motor, which rotates the crank and counterweight. This rotary motion is converted to a vertical reciprocating motion via the walking beam, which causes the end of the beam to rise and fall and produces the “nodding” motion. On the other end of the beam is a curved metal box called a horse head or donkey head. Steel cables, called a bridle, follow the curve of the horse head as it lowers and raises and thereby creates a vertical or nearly-vertical stroke.
The bridle is connected to a polished rod that passes through the so-called stuffing box. This is such a close seal that the stuffing box lets the rod move up and down without any fluid escaping. The polished rod is connected to a long string of rods called sucker rods, which run through the tubing to the pump at the bottom of the well.
This pump has two ball-check valves: a stationary valve at the bottom called the standing valve, and another valve on the piston connected to the bottom of the sucker rods that travel up and down. This valve is called the traveling valve.
When the rods start to travel up, the traveling valve is closed and the standing valve is opened (through reduced pressure) so that the fluids can enter into the bottom of the borehole through perforations that have been made through the casing and cement.
When the rods begin pushing down, the traveling valve opens and the standing valve closes (through increased pressure). The fluids now inside the casing are pushed up through the open traveling valve. When the piston then reaches the bottom of the well, it again begins its upwards path, closes the traveling valve and carries the fluid which is now above the piston up to the surface.
And if you are not already in love with Crude Oil and the nodding donkeys then here is your heart-stopper: