Fred D. Griffin, Lufkin Industries, Inc.
The American Gear Manufacturers' Association introduced its first recommendation for sizing oilfield pumping unit gear reducers in the year 1935. This recommendation eventually became AGMA Standard 422.02 and was incorporated in API Standard 11E. Since 1935 the only major change in API Standard 11E has been the addition of ductile iron as a gear material. AGMA's new standard, AGMA 422.XX, covers recommended gear ratings based on tooth strength as well as pitting resistance. The present standards, AGMA 422.02 and API llE, do not include specific recommendations for tooth strength. AGMA 422.XX also includes recommendations for sizing surface hardened gears in addition to thru hardened gears covered in the present standards. A detailed comparison between the new and old ratings, as well as the physical size of some typical oilfield pumping unit reducers, is illustrated and discussed.