Pressure Converter Valve..what is it?

[ashedd]

85 300TD

I was replacing the rubber vac lines today, car does not really want to shut off and door locks dont work, and came across a "Pressure Converter Valve". I only know the name because I searched the part number, 001 540 74 97, on allparts.

I did a search and found nothing.. I am guessing it's known as something else but I have no idea. I would like to know what its really called, what it does and how to test it.

Currently I have some hard shifting and perhaps the turbo is inop.

Thanks