Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Advancing subterranean length of pipe or cable
Reexamination Certificate
1996-09-20
2001-10-09
Hughes, S. Thomas (Department: 3726)
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Advancing subterranean length of pipe or cable
C405S174000, C029S426500
Reexamination Certificate
active
06299382
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods of using pneumatic impact tools, particularly self-propelled ground piercing tools.
BACKGROUND OF THE INVENTION
Self-propelled pneumatic tools for making small diameter holes through soil are well known. Such tools are used to form holes for pipes or cables beneath roadways without need for digging a trench across the roadway. These tools include, as general components, a torpedo-shaped body having a tapered nose and an open rear end, an air supply hose which enters the rear of the tool and connects it to an air compressor, a piston or striker disposed for reciprocal movement within the tool, and an air distributing mechanism for causing the striker to move rapidly back and forth. The striker impacts against the front wall (anvil) of the interior of the tool body, causing the tool to move violently forward into the soil. The friction between the outside of the tool body and the surrounding soil tends to hold the tool in place as the striker moves back for another blow, resulting in incremental forward movement through the soil. Exhaust passages are provided in the tail assembly of the tool to allow spent compressed air to escape into the atmosphere.
Most impact boring tools of this type have a valveless air distributing mechanism which utilizes a stepped air inlet. The step of the air inlet is in sliding, sealing contact with a tubular cavity in the rear of the striker. The striker has radial passages through the tubular wall surrounding this cavity, and an outer bearing surface of enlarged diameter at the rear end of the striker. This bearing surface engages the inner surface of the tool body.
Air fed into the tool enters the cavity in the striker through the air inlet, creating a constant pressure which urges the striker forward. When the striker has moved forward sufficiently far so that the radial passages clear the front end of the step, compressed air enters the space between the striker and the body ahead of the bearing surface at the rear of the striker. Since the cross-sectional area of the front of the striker is greater than the cross-sectional area of its rear cavity, the net force exerted by the compressed air now urges the striker backwards instead of forwards. This generally happens just after the striker has imparted a blow to the anvil at the front of the tool.
As the striker moves rearwardly, the radial holes pass back over the step and isolate the front chamber of the tool from the compressed air supply. The momentum of the striker carries it rearward until the radial holes clear the rear end of the step. At this time the pressure in the front chamber is relieved because the air therein rushes out through the radial holes and passes through exhaust passages at the rear of the tool into the atmosphere. The pressure in the rear cavity of the striker, which defines a constant pressure chamber together with the stepped air inlet, then causes the striker to move forwardly again, and the cycle is repeated.
In some prior tools, the air inlet includes a separate air inlet pipe, which is secured to the body by a radial flange having exhaust holes therethrough, and a stepped bushing connected to the air inlet pipe by a flexible hose. These tools have been made reversible by providing a threaded connection between the air inlet sleeve and the surrounding structure which holds the air inlet concentric with the tool body. The threaded connection allows the operator to rotate the air supply hose and thereby displace the stepped air inlet rearwardly relative to the striker. Since the stroke of the striker is determined by the position of the step, i.e., the positions at which the radial holes are uncovered, rearward displacement of the stepped air inlet causes the striker to hit against the tail nut at the rear of the tool instead of the front anvil, driving the tool rearward out of the hole. See, for example, Wentworth et al. U.S. Pat. Nos. 5,025,868 and 5,337,837.
Expanders are tapered, ring-shaped shells that fit over the tapered nose portion of an earth boring tool in order to widen the hole made by the tool as it passes through the ground. In this manner, a 4 inch diameter tool may be used to make a 6 or 8-inch diameter hole. The tool is often sent through to make an initial bore, and then sent through a second time with the expander in order to widen the existing hole and/or crack an existing pipe.
SUMMARY OF THE INVENTION
The present invention provides a method of removing an expander from a ground piercing tool of the type having an elongated tubular tool body with a front nose and a striker disposed for reciprocation within an internal chamber of the body to impart impacts to an impact surface for driving the tool forwardly through the ground. The expander is tightly fitted onto the nose of the tool body. The method of the invention uses a pulling device comprising a pair of arms ending in hooks and mounted at ends opposite the hooks to a yoke having a threaded hole therethrough, and a screw including a threaded stem inserted through and threadedly coupled with the hole. Suitable means such as a hex-shaped head is provided for engagement with a device for turning the screw. The method according to a first aspect of the invention includes the steps of positioning the arms with the hooks of the pulling device in engagement with a pair of rearwardly facing shoulders on the expander, positioning an end of the screw extending from the yoke in the same direction as the arms in contact with the nose of the tool, and tightening the screw against the nose of the tool using the turning device on the engaging means, thereby exerting a pulling force through the arms sufficient to disengage the expander from the nose of the tool.
According to a second aspect of the invention, a method is provided for installing an underground pipe. This method includes the steps of positioning the expander on the nose of the tool, securing the pipe to the expander, operating the tool in forward mode to pull the pipe into the ground, positioning the hooks of the pulling device in engagement with a pair of rearwardly facing shoulders on the expander, positioning an end of the screw remote from the head in contact with the nose of the tool, tightening the screw against the nose of the tool using the turning device on the engaging means, thereby exerting a pulling force through the arms sufficient to disengage the expander from the nose of the tool, and disconnecting the expander from the pipe.
The present invention further provides an apparatus for removal of an expander that is simple, convenient, and may be operated manually in either of the foregoing methods. Such a pulling device comprises a pair of arms ending in hooks, a yoke having a threaded hole therethrough, a pair of pivots connecting the arms to opposite sides of the yoke, such that the arms and yoke can assume a U-shaped configuration in which the arms extend in parallel to the threaded hole in the yoke, and a screw including a threaded stem inserted therethrough and threadedly coupled with the hole, and means configured for engagement with a device for turning the screw.
Other objects, features and advantages of the invention will become apparent from the following detailed description. It should be understood, however, that the detailed description is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 1747925 (1930-02-01), Brown
patent: 2191021 (1940-02-01), Ladd
patent: 2834100 (1958-05-01), Harsh
patent: 3410354 (1968-11-01), Sudnishnikov et al.
patent: 4738565 (1988-04-01), Streatfield et al.
patent: 5025868 (1991-06-01), Wentworth et al.
patent: 5048795 (1991-09-01), Vitale
patent: 5282696 (1994-02-01), Solomon et al.
patent: 5337837 (1994-08-01), Wentworth et al.
patent: 5350254 (1994-09-01), Fisk et al.
patent: 5494116 (1996-02-01), Wentworth
Grundocrack® Pipe Bursting System, TT Technologies, Inc., 16 pgs.
Butler Marc W.
Earth Tool Company L.L.C.
Hughes S. Thomas
Philip G. Meyers Intellectual Property Law, P.C.
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