Air-Vacuum Excavation

In the mid 1960’s the Brooklyn Union Gas Company did pioneering experimentation with an air lance, air compressor, and a vacuum truck to find a better way to dig and reduce the costs associated with the approximately 30,000 street openings they made annually for gas distribution piping repair. Today air-vacuum excavation is an accepted method of safe digging for many jobs ranging from utility work to advanced tree care. Excavating with, in particular, a CEG supersonic air jet offers a number of advantages including:

• Penetrates and dislodges most types of soil, including stiff clays, by focusing its efforts like a laser onto a concentrated spot on the soil.
• Is harmless to buried gas, water, or sewer pipes; electric lines or telecommunication cables; hazardous waste containers; and military ordnance.
• Has no hard cutting edges like picks, digging blades, or buckets.
• Is two to three times faster than hand excavation.
• Excavates rocky types of soils where a shovel cannot be used.
• Is generated using a standard, portable air compressor.
• Digs up to 50% faster and harder soils than competitive air digging tools.
• Does not diffuse its energy and momentum over 3 to 4 times the contact area as do orifices or improperly designed jets.
• Delivers at a minimum twice the momentum force per unit area to the soil than a conventional "orifice or air lance."
• Has been made in sizes from 15 to 750 scfm per depending on the excavation rate required.
• Can be used in multiples for larger excavations.
• Generates less worker fatigue / injuries than a pick or shovel.
• Breaks the soil into small pieces that are ideal for recompaction.
• Excavates the soil dry so it’s more easily vacuumed at lower levels of suction.
• Uses air that’s free from the atmosphere and always available on the job site.
• Is non-conductive when working potentially around buried electric utilities.
• Gets the particles of soil already airborne to be entrained more easily by the suction air stream.

Digging with air as opposed to digging with water offers other specific advantages:

• Unlike water jets, air introduces no liquid into the excavation that increases the volume and weight of spoil for disposal.
• Soil excavated with water becomes mud that is considered contaminated and becomes a disposal problem costing time and money.
• A high-pressure water jet can cut a plastic gas line or harm pipe coatings.
• Water can accidentally undermine adjacent areas to the excavation.
• A high-pressure water jet is dangerous to an operator since it can cut through clothes or work boots.
• Mud just dumped in an open area dries to a hardened spill and doesn’t blend in.
• Water must be paid for and transported to digging locations requiring large tanks and bigger, heavier rigs.
• Muddy conditions can undermine footing around job site.
• Splashing water is messy to contain and wet clothes are objectionable to workers.

Although exhaust nozzles for rocket engines have been designed and built for many years, supersonic air jet excavation nozzles are different. CEG has carried out extensive research into the aerodynamic design of its earth excavation nozzles. CEG has developed its own proprietary design method and CAD-CAM interface for its air jet excavation nozzles. Unlike propulsion nozzles, the energy to accelerate the air comes primarily from the release of its compression rather than from the combustion of a fuel. Because of their small size, particular attention must be paid to the effect of the boundary layer on the nozzle profile. Special tooling and computer-aided-machining is used to manufacture the nozzles. CEG continues to refine and improve its design through detailed mathematical modeling and laboratory experimentation. As trade secrets, CEG has developed the knowledge of what the parameters of the supersonic air jet need to be to dig effectively in the many different types of soil. CEG has carried out our own tests digging up simulated hazardous waste and military ordnance.

Pneumatic vacuum transport naturally matches air jet excavation as it:

• Is likewise non-contacting.
• Easily removes the material that is already dislodged and entrained into the air stream by the supersonic jets.
• Can be used in a small diameter, deep excavation (pot hole) where a hand shovel or a backhoe bucket cannot.
• Can convey the material dislodged from the surface to the desired remote location.
• Is powered by conventional rotary blowers, fans or injectors.
• Can be filtered to various degrees depending on the material being excavated and the site regulations.
• Has been made in sizes from approximately 200 to 4,000 acfm at up to 10 in. Hg vacuum.