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.

The excavation and vacuum transport of soil has its own unique set of characteristics. Soil types vary widely in grain size, particle shape, packing, moisture content, grading, plasticity, organic matter content, etc. Soils, in general, are not the free flowing material most conventionally moved by pneumatic transport. Special care must be taken in the design of the vacuum transport system to avoid the persistent problem of cohesive material clogging. CEG personnel have carried out extensive experimentation to determine how to most effectively design the supersonic air jets and vacuum transport systems to work together in an efficient and synergistic manner.

Recognized by Brooklyn Union who developed perhaps the first air-vacuum excavator in the 1960’s, key to vacuum excavation is to provide an air stream of sufficient velocity to lift and carry the material of concern through the hose from the pickup point to the disposal point. The suction, i.e. inches of Hg, necessary to accomplish this is a consequence of several items including: an inlet or pick-up loss; an acceleration loss to bring the material from rest up to its transport velocity in the hose; local losses at bends and expansions/contractions; air friction in the hose; lift of the material against gravity; and a discharge loss. For the relatively short distances and small lifts in air-vacuum excavation, the air friction loss tends to dominate. Typically air-vacuum excavation can be readily done below 10 in Hg suction. Units that use water to excavate, however, often need higher heads to move the mud that the water creates.

Tables and graphs of transport velocity for various materials are readily available in the literature. For example, an air velocity of about 5000 feet per minute is sufficient for a granular soil weighing up to about 100 lbm/cu ft. A damp clay/sandy soil or wet sand/gravel weighing up to about 130 lbm/cu ft may need up to10,000 ft/min. Horizontal hose runs are actually need higher transport velocities than vertical.