Rotational speed adjustment mechanism of a pneumatic tool

A rotational speed adjustment mechanism of a pneumatic tool, comprising:

• an intake member having a cylindrical body section, an intake inward axially extending from one end of the body section, an exhaust port inward axially extending from the other end of the body section, inner ends of the intake and the exhaust port being not communicated with each other, a lateral outlet extending from the intake through a sidewall of the body section for communicating the intake with outer side of the body section, a lateral inlet extending from the exhaust port through a sidewall of the body section for communicating the exhaust port with outer side of the body section;
• a speed adjustment valve having an annular collar which is coaxially rotatably fitted on the body section for blocking the opening of the lateral outlet, the collar being rotatable about the axis of the body section between a full speed position and a slowest speed position, a full speed through hole being formed through a sidewall of the collar, the diameter of the full speed through hole being at least equal to the diameter of the lateral outlet, at least one slow speed through hole being formed through a sidewall of the collar, the diameter of the slow speed through hole being smaller than the diameter of the lateral outlet, when the collar is turned and positioned in the full speed position, the full speed through hole being coaxially communicated with the opening of the lateral outlet, whereby the full diameter range of the lateral outlet provides a passage for the airflow, when the collar is turned and positioned in the slowest speed position, the slow speed through hole being communicated with the lateral outlet, whereby the lateral outlet is partially blocked by the circumferential wall of the slow speed through hole and simply the diameter range of the slow speed through hole provides a passage for the airflow;
• and
• a case enclosing the body section and the collar to isolate the body section and the collar from outer side, the case being formed with an internal passage defined between the case and the body section and the collar for communicating the lateral outlet with the lateral inlet.