Each actuator has a different spring rate (boost level). They can be from 5psi through to 30psi, which is the pressure that they open at. The aim is to get an actuator closest to the desired boost setting so the EBC has to do as little as possible to gain ultimate response. Some aftermarket actuators you only have to replace the springs, where others are sealed and you have to replace the entire actuator. Let me know if you need to purchase one.