Here is a flash animation of Sucker Rod Pump. This pump brings oil form underground to the earth's surface.

The chrank shaft has a counter weight in one end and the other end attached to the Pitman Arm which in turn, attaches to the Walking Beam. At the other end of the walking beam is the Horsehead which has circular shape whith rotation center is at the rotation center of walking Beam. This makes the caple always tangent to the horsehead, which pull and push polished rod perpendicular to ground level.

Below is a video of actual Sucker Rod Pump. I like it a lot, hope you like it too.