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CALTRANS FOUNDATION MANUAL
Diesel Pile Hammers
In the early 1950's a new type of pile driving hammer was introduced - the Diesel Hammer.
Basically, it is a rudimentary one cylinder diesel engine. It is fed from a fuel tank and pump
mounted directly on the hammer, in contrast to air and steam hammers which require an
external energy source. Simple to operate, diesel hammers are commonly used on most
bridge contracts today.
Single Acting Diesel Hammers. The fundamental makeup and operation of all
diesel hammers are similar. They consist of a cylinder-encased ram, an anvil block, a
lubrication system, and a fuel injection system which regulates the same amount of fuel to
each cycle. New models added a variable fuel metering system which can change the energy
delivered by the ram, thereby making them more versatile for varying soil conditions. The
energy imparted to the driven pile is developed from gravitational forces acting on the mass
of the piston. Refer to Figure 7-13.
The operational cycle of the single acting diesel hammer is shown on Figure
7-14 and is described in the following paragraphs.
To start operations, a cable from the crane lifts the ram. At the top of the stroke, the lifting
attachment is "tripped" and the ram allowed to drop.
The ram falls by virtue of its own weight and activates the cam on the fuel injector which
injects a set amount of fuel into the cup-shaped head of the impact block. As soon as the
falling ram passes the exhaust ports, air is trapped in the cylinder ahead of the ram, and
compression begins. The rapidly increasing compression pushes the impact block (anvil)
and the helmet immediately below it against the pile head prior to the blow.
Upon striking the impact block with its spherically shaped leading end, the ram drives the
pile into the ground and, at the same time atomizes the fuel which then escapes into the
annular combustion chamber. The highly compressed hot air ignites the atomized fuel
particles and the ensuing two-way expansion of gases continue to push on the moving pile
while simultaneously recoiling the ram.
As the upward flying ram clears the exhaust ports, the gases are exhausted and pressure
equalization in the cylinder takes place. As the ram continues its upward travel, fresh air is
sucked in through the ports, thoroughly scavenging and cooling the cylinder. The cam on
the fuel injector returns to its original position allowing new fuel to enter the injector for
the next working cycle. The operator may stop the hammer manually by pulling a trigger
which deactivates the fuel supply.