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Cylinder’s life is a very important index of reciprocating pump, and BUTT thread is popular used on Cylinder Block, its life is one important factors to decide cylinder’s life. This paper introduced BUTT applied on quintuple pump and it was unlocked when using sometimes first, analysis how to calculate the strength of BUTT secondly, using FEA modal analysis to find the reason of cylinder cover vibration thirdly, claim how to apply torque on BUTT and how to enhance the strength of BUTT in the end, so it is reference of design BUTT.

Reciprocating pump head body threads are mostly trapezoidal threads and U.S. serrated threads (BUTT). The trapezoidal thread is a symmetrical thread, which can be driven in both directions. Serrated thread is asymmetric thread, can only one-way force and transmission, mainly used for transmission devices, can also be used for fastening connection occasions, serrated thread tooth type is not isosceles trapezoid, root bearing area, high strength, no stress concentration at the root, to withstand the effect of unidirectional stress is good, can effectively avoid root fracture, prolong the service life. Therefore, at present, American-made serrated thread (BUTT) is widely used in reciprocating pumps (mud pumps, fracturing pumps), as shown in Fig. 1.

If the serrated thread fails, it will lead to the scrapping of the whole pump head body. When designing the threads, the selection was often based on experience in the past. In the field will appear when the use of loose gland threads, light cause leakage affecting the normal work of the hydraulic end, heavy so that the pump head body piercing the cylinder leading to the scrapping of the entire pump head body. Therefore, it is necessary to design the U.S. system serrated thread (BUTT) strength check, and the serrated thread to explore the causes of loosening.