A reversing mechanism for a pneumatically or hydraulically powered tool having a rotor adapted to selectively rotate in either one of first and second rotational directions. The reversing mechanism allows a user to actuate a button that rotates a valve to direct air flow through the tool. By pressing the button, the button will move a base laterally, and in doing so, rotates the valve. Rotating the valve distributes fluid to cause the rotor to rotate in a selected rotational direction.