Re: What makes powervalves go up?
Depending on the MFR they're either electric (cable/solenoid) or gas pressure. The gas pressure are more reliable and prevelant nowadays.
As the pressure builds up in the exhaust port it travels up a smally hole in the jug. There it creates positive pressure in a small area sealed by a piece of rubber, neoprene and/or o-rings called a "bellows". It overcomes the force of the spring and pushes the valve up. They don't go up/down with each stroke, instead they smoothly open/close and stay open as long as you're above the threshhold.
Common misconception is higher HP from powervalves, which is untrue. They just make more usable HP down low.
You don't have to flinch for me to know that you're scared.