If read the link to any other two stroke powervale you going to be mislead. This is the only "power valve of its type.
ITS ACTUALL NOT A POWERVALVE ITS AN EXHAUST VALVE.
In 1987 Suzuki went away from this style valve in favor of a variable timing ex port guillotine set up. Those will make more HP and retain low end also smoogbing transition. There main function is to raise the exhaust port timing at a certain rpm. How they make more power is that at lower rpms the are closed and build more compression due to a longer effective stroke of the piston sweeping the ex port closed. At the specified rpm the valve snaps open allowing the return wave of the pipe to stuff the cylinder later and creating more volume at the port opening to be stuffed.
Kawasaki had a different arrangement where they had triple port exhausts and open and closed them to effectivally do the same thing. But there benefit being the tripple ports scaveng the top from of the cylinder more effectivlly. In later years Kawasaki developed a guillotine in the main ex port also opening the two ports at different times and rates.