How does the oil bypass valve work?

[Hammerhead]

So according to this bulletin, all ISX's are affected prior to April 2015 then?
You purchased part # 4357177, and it was the old style pictured in the bulletin they say to discard? That doesn't seem right.
How much was the part?
Thanks Brock, it's only a lubricating oil related part...now I'm stressing! I need beer!

As far as how it works, from Quickserve:
Whenever the pressure drop across the lubricating oil filter exceeds 862 kPa [125 psi], the oil filter bypass valve opens and allows lubricating oil to bypass the lubricating oil filter.

This condition can occur during cold ambient (cold lubricating oil) engine start-ups.

The purpose of the bypass valve is to maintain lubricating oil flow to the engine and prevent an oil filter collapse.