How does the CEG supersonic air nozzle work?

The patented CEG supersonic air 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 this air moving at approximately 1200 mph is focused onto the soil dislodging it in a fraction of a second. Soil is an unconsolidated assemblage of solid particles that may or may not contain organic matter, the voids between the particles being occupied by air and/or water. The aggregate nature of soil aids the ability of the air to fracture it; while stronger materials and ones that are not porous like metal or plastic pipes or cables or even wooden tree roots are unaffected.

Why does the CEG supersonic air nozzle out perform other air jets?

In head to head tests, the CEG supersonic air nozzle dislodged harder clay soil and dug faster than other air digging tools. Soil fractures from stress, i.e. force per unit area, on its surface. As shown below for the same pressure and flow, compressed air exiting from a pipe nipple, orifice, or improperly designed nozzle expands outward rapidly to 3 to 4 times the area versus the jet from the patented CEG supersonic nozzle. The flow from these competitors can even go sub-sonic as indicated by the presence of a “Mach Disk,” which can be seen in the flow if the light is right.

In head to head tests, the AIR-SPADE ® with CEG supersonic nozzle dislodged harder clay soil and dug faster than other air digging tools. Shown below is a comparison test between the AIR-SPADE ® and two competitive air excavation tools. In the test, the first 3 inches of soil with a moisture content of 23% were excavated by each tool. The CEG supersonic nozzle worked up to 50% faster in the harder soil. In fact, in one test the where the competitive tool could not finish digging its clay test plot, the AIR-SPADE ® did.

Relative time required to excavate 1 cubic foot.

Will higher pressure make the CEG supersonic air nozzle work better?

Increasing the air pressure above 90 psig on a properly designed CEG supersonic nozzle does not lead to a proportional gain in excavation capability. For example, doubling the nozzle pressure to 180 psig increases the air jet force by only 10% and the exit momentum flux (stress seen by the soil) by only 45%. Supplying higher pressure to a nozzle designed to work at 90 psig actually un-focuses the air jet degrading performance and consuming more air.

In what types of soil will a CEG supersonic air nozzle work?

Because of its unique, focused air-jet, the CEG supersonic air nozzle works in most soils, even hard clays. Cohesive soils can be classified and described by unconfined compressive strength as shown below. Tests have shown the CEG supersonic air nozzle to be effective in compacted soils with unconfined compressive strengths well above the values listed for hard clay.

Consistency and Unconfined Compression Strength of Clays

Watering the work area ahead of time can be helpful sometimes. Watering reduces airborne dust if the soil is extremely dry. It also reduces the soil’s strength making the digging easier. Combined use of the CEG supersonic air nozzle with a low pressure water jet is effective even with extreme cases of highly compacted or sun-baked soils.

The CEG supersonic air nozzle in general will not cut through rock, since its unconfined compressive strength as shown below is much greater than for soil. In fact, soil results from the physical and chemical breakup of weathered rock. Shales, however, may be broken apart by the CEG supersonic air nozzle if the jet is directed between the laminations of the rock. Similarly, the CEG supersonic air nozzle will not dislodge hard frozen soil, which may behave like pavement or concrete.

How should I dig with the CEG supersonic air nozzle ?

The supersonic air nozzle will dislodge up to several inches deep in a medium to stiff soil. High-speed movies show that an air-jet penetrates and dislodges the soil in a fraction of a second. Unless the soil is highly compacted, dwelling on the same spot is unnecessary and tends to increase spray. The CEG supersonic air nozzle can be moved over the soil surface at a rate of about 1 to 2 feet per second. When several inches of soil have been loosened, the soil should be removed to expose a fresh working face for the air jet. Vacuum suction, as provided by our AIR-VAC ® and SAFEX ® units, is an excellent companion to the CEG supersonic air nozzle since it is likewise non-damaging.

What size nozzle should I use?

As shown below nozzles are available that use from 15 to 225 scfm of compressed air. The amount of soil that can be dislodged in a given amount of time is roughly proportional to the amount of air used. The 150-scfm nozzle is the most commonly used size for industrial applications. It has good productivity and is designed to run from the most common size of portable air compressor, a 175 to 185 scfm unit.

Excavation Rates (cu ft / min)

What size air compressor do I need to use the CEG supersonic air nozzle properly?

Air compressors are sized by pressure and flow. In the US pressure is measured in pounds per square inch above atmosphere, psig. Flow is measured in cubic feet of air per minute, cfm. Generally all air compressors will produce at least 100 psig; while flows will vary from a few cfm for small electric piston units to hundreds of cfm for gas or diesel driven portable screw compressors. All supersonic air nozzles are designed to operate best at a pressure of 90 psig, but vary in flow to match standard available compressors according to the table below. Note, a smaller nozzle may always be used on a larger compressor, but not the reverse. Trying to run a larger nozzle on a smaller compressor will result in significantly less than 90 psig being delivered and will noticeably diminish performance.

Recommended Compressor Size

What size of air hose do I need to use the CEG supersonic air nozzle properly?

Compressed air flowing through a hose experiences a drop in pressure from friction and constrictions. Friction loss is proportional to the length of the hose. The amount of air, its pressure, the hose inner diameter and its smoothness also determine the loss. The table below shows the pressure loss for 50 feet of common air hose with couplings as a function of size and nozzle flow, cfm, for air at a pressure of 90 psig. Generally, a 1-inch air hose is recommended for use with the 150 scfm CEG supersonic air nozzle.

Pressure Loss (psig) for 50 feet of common air hose

References

Bell, F.G. 1983. Engineering Properties of Soils and Rocks. 2 nd Ed. Butterworths. Pg. 1.

Rollins, J.P. Ed. 1989. Compressed Air and Gas Handbook. 5 th Ed. Prentice Hall. N.J.

OSHA Excavation Standard Handbook. ISBN 1-877798-07-X

Das, B.M. 1983. Advanced Soil Mechanics. McGraw-Hill. Table 7.5. Pg. 442. McGraw-Hill.

Nichols, H.L. Jr. 1976. Moving the Earth. The Workbook of Excavation. 3 rd Ed. McGraw-Hill

Bell, F.G. 1983. Engineering Properties of Soils and Rocks. 2 nd Ed. Butterworths. Chap. 8.

Goodyear Technical Information Cat 821-947-850