Pneumatically operated power tool having mechanism for changing compressed air pressure

1. A pneumatically operated power tool comprising:

an outer frame having a compressed air intake portion and defining therein a compressed air chamber;

a driving components disposed in the outer frame and driven by a compressed air in the compressed air chamber;

a pressure reduction valve allowing a compressed air to flow from the air intake portion to the compressed air chamber and to reduce a compressed air pressure when the compressed air is flowed through the pressure reduction valve;

a passage section provided independently of the pressure reduction valve and communicating the air intake portion with the compressed air chamber; and

a valve member disposed at the passage section and movable between a first position where the communication at the passage section between the air intake portion and the compressed air chamber is blocked, whereby the pressure reduction valve performs its inherent pressure reducing operation, and a second position where the air intake portion is communicated with the compressed air chamber at the passage section.

2. The pneumatically operated power tool as claimed in claim 1 , wherein the pressure reduction valve comprises:

a cylinder section disposed in the compressed air chamber;

a piston disposed in the cylinder section and having a pressure receiving surface facing the intake portion, the piston being slidingly movable relative to the cylinder section in a direction perpendicular to the pressure receiving surface, the pressure receiving surface being in continuous fluid communication with the compressed air chamber;

a biasing member disposed between the cylinder section and the piston for urging the piston toward intake portion; and,

a valve section movable integrally with the piston for selectively blocking a fluid communication between the intake portion and the pressure receiving surface.

3. The pneumatically operated power tool as claimed in claim 2 , wherein the cylinder section has a closed bottom end and another open end, and

wherein the valve section comprises a valve stem extending from the piston, and a valve head fixed to the valve stem; and

the pressure reduction valve further comprising a holder section disposed at the another open end and formed with a through-hole for allowing the valve stem to extend therethrough, the valve head selectively closing the through-hole, the pressure receiving surface being formed with a groove facing the holder section in communication with the through hole and the compressed air chamber.

4. The pneumatically operated power tool as claimed in claim 1 , wherein the passage section is formed with a linear central passage, a first branch passage branched from the central passage and in communication with the intake portion, and a second branch passage branched from the central passage and in communication with the compressed air chamber, the valve member movably extending through the central passage.

5. A pressure changing mechanism for use in a pneumatically operated power tool including an outer frame having a compressed air intake portion and defining therein a compressed air chamber, and a driving components disposed in the outer frame and driven by a compressed air in the compressed air chamber, the pressure changing mechanism comprising:

a pressure reduction valve allowing a compressed air to flow from the air intake portion to the compressed air chamber and to reduce a compressed air pressure when the compressed air is flowed through the pressure reduction valve;

a passage section provided independently of the pressure reduction valve and communicating the air intake portion with the compressed air chamber; and

a valve member disposed at the passage section and linearly movable between a first position where the communication at the passage section between the air intake portion and the compressed air chamber is blocked, whereby the pressure reduction valve performs its inherent pressure reducing operation, and a second position where the air intake portion is communicated with the compressed air chamber at the passage section.

6. The pressure changing mechanism as claimed in claim 5 , wherein the pressure reduction valve comprises:

a cylinder section disposed in the compressed air chamber;

a piston disposed in the cylinder section and having a pressure receiving surface facing the intake portion, the piston being slidingly movable relative to the cylinder section in a direction perpendicular to the pressure receiving surface, the pressure receiving surface being in continuous fluid communication with the compressed air chamber;

a biasing member disposed between the cylinder section and the piston for urging the piston toward intake portion; and,

a valve section movable integrally with the piston for selectively blocking a fluid communication between the intake portion and the pressure receiving surface.

7. The pressure changing mechanism as claimed in claim 6 , wherein the cylinder section has a closed bottom end and another open end, and

wherein the valve section comprises a valve stem extending from the piston, and a valve head fixed to the valve stem; and

the pressure reduction valve further comprising a holder section disposed at the another open end and formed with a through-hole for allowing the valve stem to extend therethrough, the valve head selectively closing the through-hole, the pressure receiving surface being formed with a groove facing the holder section in communication with the through hole and the compressed air chamber.

8. The pressure changing mechanism as claimed in claim 5 , wherein the passage section is formed with a linear central passage, a first branch passage branched from the central passage and in communication with the intake portion, and a second branch passage branched from the central passage and in communication with the compressed air chamber, the valve member movably extending through the central passage.