The pumping unit is the mechanism that converts the rotary motion of the prime mover into the reciprocating vertical movement required at the polished rod. Most types of pumping units utilize a walking beam, inherited from the days of the cable-tool drilling rigs. Beam-type sucker rod pumping units are basically a four-bar mechanical linkage, the main elements of which are:
1. The crank arm, which rotates with the slow-speed shaft of the gear reducer.
2. The pitman, which connects the crank arm to the walking beam.
3. The portion of the walking beam from the equalizer bearing to the center bearing.
4. The fixed distance between the saddle bearing and the crankshaft.
The operation of the above linkage ensures that the rotary motion input to the system by the prime mover is converted into a vertical reciprocating movement, output at the horsehead. The sucker rods, attached to the horsehead, follow this movement and drive the bottomhole pump. Although there are different arrangements of pumping units available, all employ the same basic component parts detailed above.
The vast majority of pumping units used worldwide belong to the beam-type class. The ratings and other technical specifications of beam-pumping units are covered by the American Petroleum Institute in its publications. Non-API pumping units are also available and are mainly used for long-stroke sucker-rod pumping or for special conditions.
The main structural parts of a common conventional pumping are built over a rigid steel base, which ensures the proper alignment of the components and is usually set on a concrete foundation. The Samson post may have three or four legs and is the strongest member of the unit, since it carries the greatest loads. On top of it is the center or saddle bearing, which is the pivot point for the walking beam. The walking beam is a heavy steel beam placed over the saddle bearing, with a sufficiently great metal cross-section to withstand the bending loads caused by the well load and the driving force of the pitman.
The well side of the walking beam ends in the horsehead, which, through the wireline hanger (bridle), moves the polished rod. The horsehead has a curvature to ensure that the polished rod is moved in a vertical direction only otherwise the resulting bending forces would quickly break the polished rod. In conventional units, the other end of the walking beam carries the equalizer bearing. To this the equalizer is connected, a short section of a lighter beam set across the walking beam, transmitting polished rod loads from the walking beam evenly to the two pitmen.
The pitmen are steel rods that connect at their lower ends to the crank arms with the wrist pins. These pins are mounted on the wrist pin bearings, which allow the required rotary movement between the parts. There are several wrist pin bearings available in the two crank arms, and by connecting the pitmen to different bearings the stroke length of the polished rod can be changed. The cranks are situated on both sides of the gear reducer and are driven by the slow-speed shaft (crankshaft) of the gear reducer. The counterweights of the conventional unit are attached to the crank arms, allowing for adjustment along the crank arm axis; this arrangement was invented by Trout back in 1926.
The proper operation of the pumping unit requires that friction losses in the structural bearings be minimal. In older units, the use of sliding (sleeve) bearings, usually made of bronze, was common. These bearings can tolerate very severe conditions with little damage but require regular lubrication. Today's pumping units, however, are almost exclusively equipped with antifriction roller bearings. These bearings are grease-lubricated and sealed, needing less maintenance than simple bronze bearings.
The remaining parts of the pumping unit are the speed reducer (gear reducer or gearbox), which reduces the high speed of the prime mover to the speed required for pumping; a brake assembly that can stop the unit at any point; and a V-belt drive and its cover. The unit is usually powered by an electric motor, but internal combustion engines are also used.
As a leading enterprise in the oil and industry, Vigor's pumping unit has many distinct features in terms of simple structure, high safety and good reliability. Vigor's excellent technical team has been constantly learning and making progress to ensure the continuous innovation and development of products. Continuous learning has been our development philosophy. Therefore, choosing to work with Vigor is choosing the best partner. Please contact us as soon as possible to get more professional service.
For more information, you can write to our mailbox:
info@vigorpetroleum.com (Erica)
mail@vigorpetroleum.com (Joppa)
