01 July 1997
circuitry. Manual controls are the simplest; however, they confine the operator of the unit to the power pack'
location, which, depending upon visibility and other factors, may not be the most convenient place from
whence to operate the machine. Remote controls allow more flexibility for the operator but are an added
expense and source of trouble for the machine.
(e) Enclosure. Some power packs have a sheet metal enclosure and some do not. The principal
advantage of an enclosed power pack is protection from weather and criminal activity. Enclosures are also
helpful if they provide sound deadening, although many do not. Open power packs are more economical and
there is better access to the parts for service.
(f) Open- and Closed-loop Hydraulic Systems. Both appear on power packs in this application.
Closed-loop systems allow for better controlled starting, running, and stopping of the machines, but have
traditionally been more complicated. Open-loop systems are more adaptable for powering other equipment.
(g) Crane Hydraulic Systems. In some cases the crane hydraulic system can be employed to
power a vibratory hammer, generally the smaller models. This eliminates the need for both an external power
pack and diesel engine. However, all other comments on control systems and operation apply regardless of
whether the crane system or an external power pack is used.
(3) Hydraulic Impact Hammers. The hydraulic systems for impact hammers are very similar to those
used with a hydraulic vibratory hammer, except that there is no clamp circuit and adaptations are made to
accommodate the intermittent flow characteristics of these hammers.
motors driven at a single frequency, which has encouraged the development of many systems to vary the
eccentric moment and thus the driving force. In some cases electric vibratory hammers can be driven from
nearby three-phase outlets, obviating the need for a generator set. The hammer thus only requires a switch
box to control it. A separate, small power pack, driven with an electric motor, is required to operate the
hydraulic clamp, if there is one. This can either be on the ground or mounted on the static overweight. Electric
systems are less and less popular because of maintenance and reliability considerations.
c. Leaders. Leaders are essential for properly guiding the impact hammer and pile downward during
driving. Their configuration is dependent upon the application.
(1) Fixed Leaders. Fixed leaders are defined as leaders which are attached by a mechanical joint at
the boom point and at the bottom of the leaders. The boom point connection should always enable the
leaders to rotate about the boom point, and should be below the top of the leaders. A typical fixed leader
setup is shown in figure 3-24. Advantages and disadvantages of fixed leaders are described in table 3-4.
Fixed leaders are generally differentiated by their spotters; these different types are described below.
(a) Conventional. These fixed leaders use either a fixed length spotter (useful only when all of the
pile on a particular job has the same batter) or a spotter with a system of holes through which pins can be run.
The batter of the leaders can thus be changed by telescoping the spotter to the desired length, lining up the
holes in both inner and outer tubes, and inserting the pins.
(b) Moonbeam Spotters. These are fixed in the usual way to the boom; however, a curved beam
at the bottom of leaders guides the leaders in rotating about the boom point. A wheeled carriage on the
leaders connects the leaders to the moonbeam. Such a leader is shown in figure 3-25. Moonbeam spotters
are generally obsolete, having been replaced by the hydraulic spotters.
(c) Hydraulic Spotters. These spotters use hydraulic cylinders to control the movement of the
spotters. Hydraulic cylinders are mounted to telescope the overall length in and out, and to pivot the spotter
ends about their connection either with the crane cab or with the leaders, or both. These spotters are very
versatile. Within their travel range they can be adjusted in an infinitely variable manner from the crane. They