The design of the Resonant Pile Driver (RPD) is revolutionary in its simplicity. The device is made up of a stationary two-way piston that houses an internal rotating spline valve. A motor turns the spline valve, which redirects the flow of hydraulic fluid through holes in the stationary piston driving an external casing up and down. The only moving part subjected to high vibrational forces is the simple external casing. The mechanical elegance of the system lies in the placement and simplicity of the central rotating spline valve. The valve is hollow and very light, resisting movement only through rotational inertia. The ultra light valve allows for nearly instantaneous changes in frequency, which allows the system to maintain resonance of the pile. The valve is situated immediately within the drive casing almost eliminating hydraulic fluid inertial effects during flow switching and minimising frictional losses. Thus the system is simple and has few moving parts subject to wear or maintenance.
A linear driver using an independently controlled frequency valve permits revolutionary control over the force produced, which is unavailable with conventional sonic drills (eccentric mass vibrators). With conventional sonic equipment the force, amplitude and power are locked to the frequency of operation (actually the square of the frequency!). The RTI resonant (sonic) drill and sonic pile driver offers independent control over the frequency, peak force and amplitude produced. Thus the full power available can be delivered at any frequency. Conversely, the force and power may be decreased at all frequencies, allowing driving of smaller piles or through sensitive soil strata. In addition the frequency and power can be adjusted very rapidly (within milliseconds) permitting real time, intelligent adjustment of the equipment in the field.
An important, patented feature of the RPD (which is not available with existing sonic drills, sonic drivers or high frequency vibrators) is the ability to tune the operating frequency of the vibrator to the changing natural frequency of the driven system. For example, as soil is compacted around the pile the system becomes stiffer and denser (more massive) and the natural frequency will tend to increase. Sonic drills rely upon the operator to make frequency adjustments or they lose efficiency. The RPD electronically monitors the performance and uses a proprietary algorithm to adjust and optimise the operating frequency to maintain resonance.
The RPD is patented in the USA, Canada, Australia, Europe and South East Asia.