Soil is an unconsolidated assemblage of solid particles including clay, sand, silt, and rock, and sometimes organic matter. Voids between the particles are occupied by air and/or water. When compressed air is directed into soil at close range, air enters the voids, expands, and fractures the soil. Stronger, non-porous materials such as metal or plastic pipes, cables, or even tree roots are unaffected.
AirSpade's proprietary, supersonic nozzle turns compressed air into a high-speed, laser-like jet moving at twice the speed of sound, Mach 2. All of the energy and momentum of air moving at approximately 1,200 mph is focused onto the soil, dislodging it in a fraction of a second.
Although rocket engine exhaust nozzles with supersonic performance have been in use for many years, supersonic air-excavation nozzles are a relatively new development. Through in-depth aerodynamic research including analysis of high-speed movies, combined with extensive knowledge of soils, AirSpade designed and developed the proprietary supersonic nozzle (US Patent #5,782,414).
Unlike propulsion nozzles, energy harnessed to accelerate the air stream comes from the expansion of air under compression rather than from the combustion of fuel. Adding to the challenge are issues relating to the effect of the air flow boundary layer on the nozzle profile. In order to meet demanding specifications and tight tolerances required, special tooling and computer-aided-machining is used to manufacture the nozzle. AirSpade continues to refine and improve the supersonic nozzle design through detailed mathematical modeling and laboratory experimentation.
AirSpade Supersonic Nozzle vs. Other Air-Jets
Soil fractures from stress (force per unit area) applied to its surface. Focusing this force results in faster, and more efficient soil excavation. As shown below, air exiting from an open pipe, or from an improperly designed nozzle expands outward rapidly to 3 to 4 times the area versus the focused air-jet on the supersonic nozzle. Consequently the AirSpade supersonic nozzle outperforms other air-jets by a wide margin.
AirSpade 2000 vs Competitive Air-Excavation Tools
In head-to-head performance tests, the supersonic nozzle equipped AirSpade dug faster and dislodged harder soils than competitive air-excavation tools. Shown in the graph below are the results from comparison tests between AirSpade 2000 and two competitive air-excavation tools. These tests were performed by the research arm of a leading tree care company and were conducted under carefully controlled conditions. In each test, 1 cubic foot of soil of uniform moisture content was excavated to a uniform depth of 4 inches, in an identical manner, by each tool. Four iterations of each test were performed and the results were totaled.
When all is said and done, faster digging with AirSpade means less worker fatigue, lower energy costs, and shorter job cycles!