Larry Teel, American International Mfg. Corp.
The landmark paper on beam pumping unit permissible load diagrams was presented in 1960 by Mr. Robert H. Gault (1). A permissible load diagram is simply a plot of the positive gearbox torque rating (converted to pounds of polished rod load), versus polished rod position. This plot is valid for any given counterbalance effect (CBE) and pumping unit. It enables such things as quickly telling whether a given unit is overloaded, comparing different unit geometries, or comparing effects of different CBE levels. Higher water cuts and deeper wells are more common in today's world. To maximize production rates, operations are moving toward longer stroke lengths, larger pump plungers, and higher CBE levels. Negative gearbox torque becomes a factor at higher CBE, and has not been presented in previous literature on permissible loads. This paper presents the permissible envelope, which accounts for both positive and negative gearbox torque rating. Permissible envelopes enable more complete definition of acceptable pumping unit rod loads than has been available in the past.