Taken from another thread:
I started out with the hardness right in the middle. To set this, you tighten the knob all the way to full hard then loosen it three full turns. With this setting, go for a test drive and listen to the valve’s operation. You should be getting a nice even release of air with a 2nd gear WOT pull (pick a good road for this and watch the speed limit). If you are getting a fluttered release, loosen the valve in quarter turn increments until you hear the right valve release. When you are satisfied, take it out on the highway and go through the gears and listen to the valve (again watch your speed). This is a good time to take note of your max boost pressure if you have a gauge. If everything is set right, all gears should have a nice even release and your max boost pressure should be normal and holding. At this point, you can make minor adjustments to dial it in right where you want it.