High velocity pneumatic devices are used in construction work to excavate or dislodge soil from around electrical cables, water pipes, gas mains, and the like. The pneumatic device has the advantage of being capable of pulverizing the soil without damaging the utility lines.
The typical high velocity pneumatic device consists of a body or housing which carries an elongated tube. The body is connected to a source of air under pressure, such as a compressor, and a valve mechanism mounted in the body controls the flow of air to the tube. Mounted in the distal end of the tube is a nozzle which is designed to increase the velocity of the air being discharged from the tube toward the soil. The typical nozzle is provided with an inwardly converging upstream end which merges into a diverging downstream end. This configuration acts to reduce the pressure of the air and increase its velocity. High velocity pneumatic devices have also been employed to remove dislodged soil or other material. The evacuation device includes an elongated rigid tube and air under pressure is supplied through jets into the distal end of the tube and directed inwardly of the tube away from the distal end, thus creating an aspirating action to draw material through the tube. In use, the elongated tube is positioned over the shoulder of the operator and the material is discharged form the upper end of the tube behind the operator.