Excavating – Ditcher
Patent
1999-12-02
2000-12-12
Pezzuto, Robert E.
Excavating
Ditcher
239532, E02F 502
Patent
active
061581526
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to excavators and, more particularly, to hand-held pneumatic excavators.
2. Description of the Prior Art
Since the 1960's, contractors have used compressed air exiting from the end of an open pipe for cleaning operations. Such uses include loosening soil from around buried water pipes, gas mains, electrical cables and the like in small hole excavations. Previously, picks, digging bars, spades, buckets or blades having hard cutting edges were used to uncover a buried object and often caused significant damage to the buried object. The use of compressed air has the advantage of pulverizing most soil types without damaging the buried object.
Pneumatic devices which use compressed air to uncover buried objects typically include a source of air under pressure, such as a compressor connected via a valve mechanism to an elongated tube. The valve mechanism controls the flow of compressed air through the tube.
However, compressed air exiting from the open end of a tube expands suddenly to atmosphere in an unfocused, complicated and wasteful manner. To improve performance of compressed air excavators, a nozzle is incorporated on the exit end of the tube. Typically, the nozzle has an inwardly converging upstream end which merges into a diverging downstream end. This configuration acts to reduce the pressure of the air or gas and increase its velocity. European Patent No. 0 251 660 describes a typical pneumatic hand tool based upon this design. U.S. Pat. No. 5,170,943 shows a similar high velocity pneumatic excavating hand tool having a valve connecting a pressurized gas supply to a non-conductive tube having a terminal nozzle.
However, little attention has been paid to the proper engineering design of the nozzle for excavation purposes. Excavation results appear to be empirically based; some prior art devices supposedly provide results which do not correspond to gas dynamic relations governing the performance of these nozzles. To achieve the air exit velocities cited in one of these latter devices, it would have to be supplied with compressed air at over two hundred psig (pounds per square inch gauge). This is well over double the one hundred psig normally used in the trade and generally available from a conventional portable air compressor. Previous devices, hence, have been energy inefficient and wasteful.
In addition, these prior art devices generate a large amount of dust and debris blowback at the operator during digging operations. This is due both to an over use of compressed air and the unfocused and highly dissipative nature of the nozzles. In an extreme case, standing shock waves may be formed downstream of the nozzle exit. These shock waves suddenly decelerate the air jet speed from supersonic to subsonic with concomitant loss of excavation ability.
Conventional portable air compressors which serve as the gas supply for prior art devices are constrained because the range of the effective working distances of the prior art devices is limited by the length of an air hose from the air compressor, generally no more than fifty to one hundred feet. Because conventional portable air compressors generally must be towed into position by other vehicles, they are limited to roadways and to areas adjacent to level or smooth areas capable of being traversed by vehicles. Farm lands, fields, water holes, forested or rocky areas are difficult to reach effectively in this manner.
Since the late 1970's, there has been considerable work towards developing small, inexpensive, portable, high flow air units. These are typically used to blow away leaves, grass clippings and the like from in front of an operator. U.S. Pat. No. 4,288,886 discloses an air broom system which includes a housing, a portable power unit, a rotary impeller unit and a tube from which air exits. U.S. Pat. No. 5,195,208 discloses a backpack power blower apparatus made up of a frame supporting an engine, a blower and associated parts, including sound insulation. Although these prio
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patent: 3645450 (1972-02-01), Calder
patent: 4288886 (1981-09-01), Siegler
patent: 5170943 (1992-12-01), Artzberger
patent: 5195208 (1993-03-01), Yamami et al.
patent: 5291819 (1994-03-01), Hambric
Apt, Jr. Jerome
Brumbaugh Paul M.
Nathenson Richard D.
Uram Martin J.
Concept Engineering Group, Inc.
Pezzuto Robert E.
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