Why Auto-Lok Nuts is used to fasten compressor valves?

Your advantages to switch over to a Auto-Lok Nut:
1)      Single piece Auto-Lok Nut that does not require specific knowledge or multiple tools for installation
2)      A locking fastener with prevailing torque that functions completely independent of any preload
3)      50% quicker installation
4)      Consistent prevailing torque enabling exact bolt tensions to be achieved with each installation
5)      Reduce inventory (single piece instead of two pieces) eliminating of mix-ups when matching top and bottoms
6)      No galling and consistent friction coefficients for stainless steel utilizing a unique, permanent tin based anti-galling treatment

typically on compressor valves sherardisation is done on the stainless steel 316L Auto-Lok Nut.
this is a zinc treatment in an oven of 400°C, dust of zinc is combined with an inert material  such as sand.

The deposit is created while parts are rotated very slowly