The steam, or pneumatic, hammer has basicallyreplaced the drop hammer. This hammer (fig. 12-60)consists of a cylinder that contains a steam-driven orair-driven ram. The ram consists of a piston equippedwith a striking head. The hammer is rested on the buttor head of the pile for driving.Figure 12-60.— Steam, or pneumatic, pile hammer.With a single-action steam, or pneumatic, hammer,the power drive serves only to lift the ram; thedownward blow of the ram results from the force ofgravity only. In a double-action hammer, the ram isboth lifted and driven downward by the power drive. Adouble-action hammer weighs from 5,000 to 14,000pounds, and a single-action hammer weighs about10,000 pounds.The blows of the double-action hammer are lighter,but more rapid than those of the single-action hammer.The double-action hammer generally drives lightweightor average weight piles into soils of average density.The rapid blows tend to keep the pile in motion, therebyreducing the resistance of inertia and friction. However,when you are driving heavy piles in hard or dense soil,the resistance from inertia and friction, together with therapid, high-velocity blows of the double-action hammer,tends to damage the butt or head of the pile.The single-action hammer is best for driving heavypiles into hard or dense soil. The heavy ram, striking atlow velocity, allows more energy to be transferred intothe motion of the pile, thereby reducing impact anddamage to the butt or head of the pile.A conventional pneumatic hammer requires a600-cubic-foot-per-minute compressor to operate, andthe diesel is a self-contained unit constructed in sizesthat deliver up to 43,000 foot-pounds of energy per blow.The diesel pile hammer is about twice as fast as aconventional pneumatic, or steam, hammer of like sizeand weight.Diesel Hammer OperationThe most common diesel hammer used in the NCFis the DE-10 McKiernan-Terry pile hammer shown infigure 12-61. The hammer is lifted and started by asingle crane load line connected to a trip mechanism(A). The hammer is started by lifting the ram piston (B)with the load line until the trip mechanism (C)automatically releases the ram piston. The ram pistonfalls and actuates the cam of the fuel pump (D) thatdelivers a measured amount of diesel fuel that falls intoa cup formed in the top of the anvil (E). Continuing itsdownfall, the ram piston blocks the exhaust ports (F) andbegins compression of air trapped between the rampiston and the anvil. The compression of the trapped aircreates a preloading force upon the anvil, the drive cap,and the pile. The gravity propelled ram piston strikesthe anvil, delivering its impact energy to the pile.The rounded end of the ram piston mates perfectlywith the cup in the anvil and displaces the fuel at the12-42
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