Locknuts

[JohnNash]

When assembling our very large pumps we have to use a locknut arrangement on the tie bars that hold the pump sections together. The locknut arrangement comprises two machined nuts face to face on a thread (up to M80). One of the nuts is a full nut, the other is a half nut. Which of these should be on the top, the full nut or the half nut and which of these should be torqued to the correct spec?

 

[evelrod]

Usually the full nut carries the total clamping force of the fastener and the shear nut (half nut) is installed last to "lock" the assembly. Crude but effective. I have seen such properly installed assemblies back off in high vibration applications.

Rod

 

[sdz]

According to the Ajax Fastener Handbook the half nut is put on first and the full nut is put on second. A full explaination of the logic for this is in the handbook.