IMPACT DRIVER

A power tool comprises a housing, a motor assembly and an impact assembly configured to be driven by the motor assembly. The impact assembly comprises a hammer defining a hammer chamber therein and an anvil at least partially disposed in the hammer chamber and configured to rotationally drive an output shaft. The anvil comprises a body portion, an anvil chamber defined therein, and a reciprocating member configured to selectively move radially outwardly relative to the body portion to be selectively impacted by an impact member of the hammer so that the hammer selectively imparts rotational movement to the anvil. The anvil includes an active valve configured to control discharge of fluid from an anvil chamber to the hammer chamber. The active value variably opens based on variance of one or more physical characteristics of the fluid (e.g., at least one of volume, temperature, pressure, or viscosity of the fluid).