Ok, I guess we're missing something because of the language difference.

The plunger WILL move but when adjusting preload do not be surprised if the valve spring moves first - lifters do not bleed down fast.

I have never heard of a hydraulic lifter being adjusted so the plunger is in the center of travel. Before doing this I suggest you read what the manufacturer's suggested preload is and go with that.

I still suggest spinning the pushrod to find zero as in my previous post. You spin the pushrod as you tighten the adjuster screw. When you can't spin the pushrod then you are at zero preload. Now turn the adjuster screw the recommended amount and tighten the nut. Done ... move on to the next.

If you've been playing with these for a while and you aren't sure where you are, back them all off and prime the oil system by hand. Remember to rotate the crank so both sides get pressurized. Now start adjusting using the above method and the manufacturer's recommended preload.

The following is from Lunati's Race Hydraulic Lifters:
The Hydraulic Race Lifters have a pre-load that can be set to .000"-.030" and are the best option for racers looking to go beyond a stock replacement lifter.