Impulse driver

A power tool comprising:

• a housing;
• a motor positioned within the housing;
• and
• an impulse assembly coupled to the motor to receive torque therefrom, the impulse assembly including
• a cylinder at least partially forming a chamber containing a hydraulic fluid,
• an anvil positioned at least partially within the chamber,
• a hammer positioned at least partially within the chamber, the hammer including a first side facing the anvil and a second side opposite the first side;
• a biasing member biasing the hammer towards the anvil, and
• a valve movable between a first position that permits a first fluid flow rate of the hydraulic fluid in the chamber from the second side to the first side, and a second position that permits a second fluid flow rate of the hydraulic fluid in the chamber from the first side to the second side,
• wherein the chamber is a first chamber, and wherein the cylinder defines a second, expansion chamber in fluid communication with the first chamber.