It was in this gloomy situation that Vulcan designed and produced one of the most innovative products it had ever produced, the 400 vibratory hammer, the first of Vulcan's high-frequency machines.

High frequency (~2400 RPM, not to be confused with the ~7200 RPM resonant machines) vibratory drivers had been produced in Europe. Depending upon the soil conditions and configuration of the pile, the vibrations used to drive or extract the pile can also be transmitted to neighbouring structures. Since European contractors drove piles more frequently in close quarters with sensitive structures than their American counterparts, European vibratory manufacturers produced high frequency machines first. Their higher frequency, combined with lower amplitude for the dynamic force, reduce the transmitted vibrations through most soils.

Vulcan's rationale for a high frequency machine, however, was somewhat different. The first impetus for the 400 was the development of aluminium sheet piling, which made development of a driver smaller than the 1150 attractive. MKT had already developed a medium-frequency small machine (the V-2) to drive aluminium sheet piling, but the machine a) weighed over a US ton and b) had a clamp suited to steel piling, which mangled the heads of aluminium sheets.

What was needed was a lighter machine whose clamp was easier on the pile. Vulcan's interpretation of the theoretical data led it to believe that a high frequency machine would drive the piles (which was certainly the case with the lighter sheeting sections.) The result was the first 400 vibratory hammer, designed and built in the summer of 1987.

Above: the 400's first job, driving aluminium sheet piling for a marine in Ft. Pierce, FL, 15 September 1987. (Note: the designation "400" was an attempt at an equivalent rating with medium-frequency machines. The hammer actually turned 200 in-lbs of eccentric moment 2400 RPM, for a dynamic force of 17 U.S. tons.)

The 400 had several innovative features:

• A one piece gear-eccentric, machined out of plate with the eccentric weight burned out. The gear teeth were a much smaller pitch than their medium frequency counterparts, a feature replicated on the "A" series machines four years later. The small pitch ran more quietly an dispensed with the need for surface hardening.
• A clamp that was burned out of plate. The cylinder bolted to it used the flat end of the rod as the movable jaw. This only left a shallow round dent in the sheeting when clamped.
• The "U" configuration which wrapped around the exciter case and transmitted the force from the crane to the pile during extraction. This and other features were subject to U.S. Patent 4,819,740. (This patent has been a nuisance to Vulcan's competitors for long time, cited in several patents from inventors at HPSI, APE, J&M, ICE and MGF.)
• It was the first Vulcan pile driving machine to completely dispense with castings.

The result was a machine that weighed only 1100 lbs.--half of the MKT V-2--and still drove the piles successfully.

Above: another view of the 400. The cruciform suspension added bias weight to the machine. Note that the clamp is rotated differently than the first unit; this is due to the fabricated design, which allowed easy orientation of the clamp body for various sheeting sections.

Above: the entire 400 package. The power pack, Vulcan's first open unit, was an HPSI unit.

Above: the 400A. The 400 was a successful hammer, but suffered from two drawbacks: the curved lower surface made attaching accessories such as caisson beams difficult, and the suspension was not configured for down crowding, which limited excavator operation. The 400A was designed to overcome both of these problems, although Vulcan's woes a the turn of the millennium limited the company's ability to take advantage of them.

Above: the 1400, driving sheeting for a creosote plant environmental remediation in Chattanoga. The 1400 incorporated many of the features of the 400, including the curved eccentric case (which was mated to the 7" clamp.) The original suspension was an H-beam, but this proved too light for bias weight, and was replaced by the cast unit shown.

Above: The Vulcan 2800, the largest of its high-frequency machines, driving H-beams in Cairo, Egypt. It was an innovative design, and the first to actually wrap the hoses through the suspension. Unfortunately its introduction was plagued with component problems. The most serious of these was the Morse shear fenders used for the suspension springs. Having been used successfully by ICE and other manufacturers, the Morse factory began to experience quality problems of its own around the time the 2800 was introduced.

Note the use of aluminium bearing covers. These were used to afford better heat dissipation to the bearings. The high frequency machines were especially prone to overheating because of their higher rotational speed, although Vulcan also used them on their other machines, if for no other reason than they looked good.

Above: Vulcan 2800 hammer, driving sheet piles for a cofferdam used in the construction of a new bridge for U.S. 41 over the Sequatchie River in Tennessee.