spool valve chrome vs case hardened

[lfw618]

I have run into spool valves in directional control blocks, that are both case hardened, and hard-chrome plated. The spools are in very similar assemblies, and function almost identically. I am having trouble figuring out why some are case hardened, and some are chrome plated? I have looked through materials that state sometimes valves are case hardened, and sometimes chrome plated, but does not give any reasoning as to the design logic behind the difference. Any insights on this are much appreciated.

Thanks in advance!

 

[gerhardl]

Probably different factories or models, determined by experience to be 'best/cheapest'. For mechanical devices material choice are often made by somebody trying something, - and it works! Not necessary any deep analysis here, but could of course be...!

 

[lfw618]

Ahh ok, the valves are actually from slightly different configurations of the same general model. But I guess I could see the difference just being best practice/cheapest based on factory or supplier. Thank you for the response!