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; and

a change-over mechanism which is separate from the pressure reduction valve and the air chamber and which is in communication with the pressure-reduction valve, the change-over mechanism providing a first position to connect the pressure reduction valve to an atmosphere for supplying a compressed air from the intake portion to the compressed air chamber through an operation of the pressure reduction valve and a second position to connect the pressure reduction valve to the compressed air chamber for making the pressure reduction valve inoperative.

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 combination of the cylinder section and the piston defining therein a cylinder chamber;

a biasing member disposed between the cylinder section and the piston for urging the piston toward intake section; 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 an 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 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 3 , wherein the change-over mechanism comprises:

a passage section formed with a linear central passage, a first branch passage branched from the central passage and in communication with the compressed air chamber, a second branch passage branched from the central passage and in communication with an atmosphere, and a third branch passage branched from the central passage and in communication with the cylinder chamber; and

a change-over valve extending through the central passage, and linearly movable between the first position providing a fluid communication between the cylinder chamber and the atmosphere and shutting off a communication between the cylinder chamber and the compressed air chamber, and a second position providing a fluid communication between the cylinder chamber and the compressed air chamber and shutting off a communication between the cylinder chamber and the atmosphere.

5. The pneumatically operated power tool comprising as claimed in claim 1 ,

wherein the change-over mechanism includes at least a valve member movable with respect to a passage section.

6. 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; and

a change-over mechanism which is separate from the pressure reduction valve and the air chamber and which is in communication with the pressure-reduction valve, the change-over mechanism providing a first position to connect the pressure reduction valve to an atmosphere for supplying a compressed air from the intake portion to the compressed air chamber through an operation of the pressure reduction valve and a second position to connect the pressure reduction valve to the compressed air chamber for making the pressure reduction valve inoperative.

7. The pressure changing mechanism as claimed in claim 6 , 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 combination of the cylinder section and the piston defining therein a cylinder chamber;

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

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

8. The pressure changing mechanism as claimed in claim 7 , wherein the cylinder section has an 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 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.

9. The pressure changing mechanism as claimed in claim 8 , wherein the change-over mechanism comprises:

a passage section formed with a linear central passage, a first branch passage branched from the central passage and in communication with the compressed air chamber, a second branch passage branched from the central passage and in communication with an atmosphere, and a third branch passage branched from the central passage and in communication with the cylinder chamber; and

a change-over valve extending through the central passage, and linearly movable between the first position providing a fluid communication between the cylinder chamber and the atmosphere and shutting off a communication between the cylinder chamber and the compressed air chamber, and a second position providing a fluid communication between the cylinder chamber and the compressed air chamber and shutting off a communication between the cylinder chamber and the atmosphere.

10. The pressure changing mechanism as claimed in claim 6 , wherein the change-over mechanism includes at least a valve member movable with respect to a passage section.