Although it never went into production, the Single-Compound hammer was one of Vulcan's more interesting experimental hammers, and under different market circumstances had the potential of success.

Although a general long-term success, Vulcan always recognised that the product life of the air/steam hammer line wasn't infinite, especially offshore. Given the difficulties of developing an underwater hammer, Vulcan decided it needed a hammer that:

• Was, if anything, simpler than the hammer it had been producing;
• Was less subject to endless rebuilding; and
• Had lower steam or air (energy) consumption, which was an issue relative to both diesel hammers and the Menck hammers, which used the steam expansively.

The last point was best acheived if Vulcan hammers themselves used the steam or air expansively. Vulcan was no stranger to this; the California series of hammers did so for nearly three decades, albeit with a valve system that was tricky to manufacture. MKT added complexity to this scenario with their "C" series hammers. These in turn were the basis of the "Airmizer" hammers which Vulcan built under licence from Horn Construction in New York.

The solution to this came from the linear vibrator, which had a piston type ram with slots admitting air at the end of the stroke and the air expanding upon closure of the slots to push the ram towards the other end. It was a simple step to make this process "one-ended" and produce a hammer which operated in the same way, only in this case throwing the ram upwards and allowing it to fall downward and impact the pile, compressing the air after it passed the exhaust ports.

Below: a layout of the Single-Compound hammer, in this case the SC-1 (1000 kg ram) size. The hammer was single acting in its energy development but compound in the expansive use of the air or steam, thus the designation "single-compound."

The concept for this was first developed in late 1981, and plans began after that to build a prototype. The prototype had a 300 pound ram, and was built entirely at the Special Products Division in West Palm Beach. The prototype was tested successfully in the Spring of 1983.

Right: the prototype of the Single-Compound hammer with its 300 pound ram, being tested in the West Palm Beach facility. One of the major results of the tests was that the hammer's short admission time required a receiver tank on the hammer itself, and this was added to the actual field prototype.

With the sucess of the small prototype, the field prototype, the SC-3 (with a 3000 kg ram, photo at beginning of article) was built. It was tested twice on projects in West Tennessee in the summer of 1983. The tests were successful, although they indicated that the ports on the hammer needed lowering to increase the impact velocity of the ram. (Diesel hammers also slow their rams down considerably by the compression of the air before impact and combusion, which has led to the derating of these hammers' rated striking energy.)

Although the hammer worked well, Vulcan did not pursue it for two reasons:

• The offshore market collapsed with the oil prices, which removed on of its potential markets.
• The rise of dynamic testing on shore led many state DOT's to require a stroke control feature on hammers to prevent tension cracking during easy driving of concrete piles. The SC hammers did not have this.

Nevertheless the Single-Compound hammer was one of the more interesting research and development projects that Vulcan undertook.