DRIVING IN HIGHLY URBANIZED AREAS AND IN THE VICINITY OF FRAGILE STRUCTURES
 
Vibratory hammers can be classified into three types:
 
- Low frequency: typically electric hammers
- Normal frequency: hydraulic vibratory hammers like the 416L 815C and 1412C
- High frequency: resonance free vibratory hammers equipped with variable moment technology like the 20RF 28RF and 50RF
 
In low and normal frequency hammers the eccentric moment increases in step with the hydraulic oil flow from the hydraulic pump in the power pack. When passing the critical frequency area during start-up and stop the constant amplitude will cause disturbing vibrations in the boom of the crane and in the soil; not just at the working area but within a considerable perimeter distance. When working in highly urbanized areas or in the vicinity of fragile structures these vibrations may also cause damage to nearby structures. In applications such as these normal frequency vibratory hammers may not be a viable choice and contractors will need to choose a high frequency vibro hammer instead.
 
High frequency hammers like the 20RF and 28RF are fitted with variable moment that can adjust the RPM from 0-2300 eliminating critical vibrations during start-up and shut-down. After passing the critical soil frequency area the eccentric weights are automatically adjusted and synchronized to the hammers existing eccentric moment. RF hammers work well with mobile cranes.
It works as follows: 
During the start-up of the vibro hammer to the maximum frequency of 2300 rpm the eccentric moment is '0'. The eccentric weights cancel each other out and no vibrations (amplitude) are generated. The re-positioning of the eccentric weights is fully automated. Manual control for shifting the eccentric weights is possible allowing you to work with the most ideal amplitude for each soil type.