Sliding pressure control valve for pneumatic hammer drill

A method of controlling a pneumatic device comprising the steps of:

• slidably fitting a ported valve over a feed tube of the pneumatic device;
• constraining motion of the ported valve via a compliant biasing device, and providing asymmetric timing for extending pressurization of a power chamber of the pneumatic device and for reducing pressurization of a return chamber of the pneumatic device;
• and
• maintaining the ported valve between a first point along the feed tube and a second point along the feed tube, the compliant biasing device is in a rest position when the ported valve is at the first point and the compliant biasing device is in a non-rest compressed position when the ported valve is at the second point, the second point along the feed tube is closer to a drill bit than the first point along the feed tube.

A method of controlling a pneumatic device comprising the steps of:

• slidably fitting a ported valve over a feed tube of the pneumatic device;
• and
• constraining motion of the ported valve via a compliant biasing device, and providing asymmetric timing for extending pressurization of a power chamber of the pneumatic device and reducing pressurization of a return chamber of the pneumatic device, wherein a reciprocating piston of the pneumatic device has an overall stroke length, and wherein the reciprocating piston cycles between a power stroke portion and a return stroke portion, and wherein the step of providing asymmetric timing comprises using the ported valve to:
• a) control a point during the power stroke at which air flow from the feed tube to the power chamber is terminated during the power stroke, thereby permitting a termination point that is closer to the piston impact point, and also providing for the ability to pressurize the power chamber over a longer extent of the overall stroke, which improves overall efficiency;
• b) control a point during the return stroke at which air flow from the feed tube to the power chamber is initiated during the return stroke, thereby permitting a power chamber pressurization point that is farther from the piston impact point than when air flow was terminated during the power stroke, and also providing for the ability to create a greater overall piston stroke length by delaying onset of pressure in the power chamber, during return motion of the reciprocating piston, which causes it to decelerate when it is moving away from a drill bit;
• c) control a point during the power stroke at which air flow from the feed tube to the return chamber is initiated during the power stroke, thereby permitting an initiation point that is closer to the piston impact point, and also providing for the ability to delay pressurization of the return chamber prior to piston impact;
• and
• d) control a point during the return stroke at which air flow from the feed tube to the return chamber is supplied during the return stroke, thereby permitting a pressure supply point that is farther from the piston impact point than a point at which pressurization was terminated during the power stroke, and also providing for the ability to start pressurizing the return chamber closer to the back end during the return stroke, as compared to the power stroke producing a longer overall piston stroke length.