Figure 12-61.-Operating principles of the McKiernan-Terry diesel pile hammer.precise moment of impact for perfect timing. The fuelis atomized and splattered into the annular (ring-shaped)zone between the ram and the anvil and is ignited by theheat of compression.The resulting explosive force drives the rampiston upward and the pile downward and adds a pushto the pile to extend the time of the total effort to drivethe pile.On the upstroke, the ram piston opens the exhaustports (F) to permit scavenging the exhaust gases. Theram piston continues freely upward until arrested bygravity.The length of the stroke varies with theresistance of the pile.The greater the resistance, thelonger the stroke.Having reached the top of its stroke, the ram pistonfalls again, repeating the cycle. The hammer is stoppedby pulling a rope (G) that disengages the fuel pump cam(D).TRIP MECHANISM.— The trip mechanism (fig.12-62) is an off-center linkage mechanism located at therear of the hammer, designed to lift and drop the ram forstarting. Additionally, the trip mechanism lifts andlowers the hammer in the leads. The trip mechanism isconnected to a single line from the crane. Lowering thetrip mechanism to the bottom of its stroke engages thelifting lever that lifts the ram. When the crane lifts thetrip mechanism and ram piston past the upper stops, thefinger of the trip lever is rotated clockwise around thetrip lever pin, thus freeing the ram piston. The tripmechanism is held in the upper position while thehammer is in operation.The safety link in the trip mechanism is designed tobreak or bend should the operator lower the tripmechanism to low and engage the lifting lever while thehammer is in operation.The safety link preventsdamaging the trip mechanism or ram. If the safety linkis broken while the hammer is in operation, the hammerwill continue to operate; however, once the hammer isshut down, the safety link must be replaced before thehammer can be restarted.12-43
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