This invention relates to pneumatic tools in general and more particularly to pneumatic tools of the type shown in U.S. Pat. Nos. 4,040,554, 4,122,904, 4,227,637, 4,196,833, 4,253,598, 4,339,065, 4,346,831, 4,497,377, and 4,763,562.
These tools typically comprise a housing, a cylinder disposed in the housing, a piston slidably mounted in the cylinder, a hammer connected to the piston, selectively actuated operating means for causing the piston to reciprocate within the cylinder so as to drive the hammer from a first retracted position to a second extended position, and a nozzle section for receiving a fastener and positioning it for engagement by the hammer in order to permit the hammer to drive the fastener from the nozzle into a workpiece as the hammer is driven from its first retracted position to its second extended position. The operating means for causing the piston to reciprocate typically comprises a control valve that is operated by a manually-actuated trigger, and means responsive to operation of the control valve for selectively (a) applying a high pressure gas to one (top) side of the piston so as to urge the piston to move the hammer through its drive stroke or (b) relieving high pressure gas from the one (top) side of the piston so as to permit the piston to move the hammer through its return stroke. In addition, such tools include safety means for preventing the operating means from causing the hammer to move through its drive stroke until the safety means is operated. The safety means generally comprises a safety valve for selectively (a) applying high pressure gas to the other (bottom) side of the piston so as to urge the piston to move the hammer through its return stroke or (b) removing high pressure gas from the other (bottom) side of the piston so as to permit the piston to move the hammer through its drive stroke. The safety means also usually comprises an actuating member (commonly called a "safety rod") arranged to operate the safety valve when the actuating member is depressed, with the actuating member normally protruding through the nozzle section of the tool far enough to assure that it will be depressed by a workpiece when the nozzle section is brought up against that workpiece.
Heretofore various designs have been conceived and employed for assuring that the tool will not be fired accidentally. However, although such prior designs have improved safe use of such tools, there remains a possibility of malfunctioning of the tool.