Method and apparatus for replacement of underground pipe

A method for replacement of an existing pipeline using a directional boring machine having a drill string and an impactor mounted at a terminal end of the drill string, which impactor includes a bursting head, a striker which delivers impacts to the bursting head, a pressure fluid-actuated impact mechanism and a valve regulating supply of pressure fluid to the impact mechanism, which method comprises:

• (a) inserting the drill string through the pipeline;
• (b) connecting a distal end of the drill string to the impactor;
• (c) pulling the drill string and impactor into the pipeline while drawing a replacement pipe behind the impactor;
• (d) actuating the impactor by pulling on the drill string, which causes the valve to supply pressure fluid to the distributing mechanism;
• and
• (e) stopping the impactor by reducing pulling force on the drill string.

An impactor for use with a directional boring machine having a drill string, comprising:

• a head having a rearwardly opening recess and a front end opening that communicates with the recess;
• an inlet pipe connected at its front end to a distal end of the drill string and extending into the recess of the head through the front end opening;
• a striker mounted for sliding movement along the inlet pipe;
• a distributing mechanism responsive to pressure fluid supplied through the drill string and inlet pipe to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the head;
• a tubular housing in which the striker and distributing mechanism are mounted, which tubular housing comprises a rearwardly extending portion of the head;
• a pulling connection by which the impactor can be pulled by the drill string while the striker is delivering impacts against the head in the same direction as a pulling force exerted by the drill string;
• and
• a tubular pulling adapter secured to a rear end opening of the tubular housing and connectable to a coaxial replacement pipe at a rear end thereof, the pulling adapter having a sealing wall therein which prevents exhaust from the distributing mechanism from entering the replacement pipe.

A method for replacement of an existing pipeline using a directional boring machine having a drill string and an impactor mounted at a terminal end of the drill string, which impactor includes a head, a striker which delivers impacts to the head, and a pressure fluid-actuated impact mechanism, which method comprises:

• (a) inserting the drill string through the pipeline;
• (b) connecting a distal end of the drill string to the impactor;
• (c) pulling the drill string and impactor into the pipeline while drawing a replacement pipe behind the impactor with a front end opening of the replacement pipe in a sealed condition;
• (d) operating the impactor as needed to burst the pipeline by supplying a pressure fluid to operate the impactor, the pressure fluid including a lubricant;
• and
• (e) injecting exhaust pressure fluid including the lubricant from the impactor outside the impactor and replacement pipe.

An apparatus for replacement of an underground pipe, comprising:

• an impactor including a bursting head having a rearwardly opening recess, a striker mounted for sliding movement within the head, a distributing mechanism responsive to pressure fluid supplied through an inlet to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the head, and a pulling connection by which the impactor can be pulled while the striker is delivering impacts against the head in the same direction as a pulling force;
• a length of cable engagable to the connection at the front end of the impactor for delivering the pulling force;
• and
• a cable pulling system that pulls the cable in a plurality of repeated cyclic pulling strokes, including a holder that engages the cable and a cylinder having a movable piston operative to move the holder along the pulling stroke.

An impactor for use as part of an apparatus for replacement of an underground pipe, comprising:

• a bursting head having a rearwardly opening recess;
• a striker mounted for sliding movement within the head;
• a distributing mechanism responsive to pressure fluid supplied through an inlet to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the head;
• an inlet pipe extending into the recess of the head for supplying compressed air to the distributing mechanism, which inlet pipe has a rear end opening configured for connection to an air hose for supplying compressed air to the distributing mechanism;
• a pulling connection disposed at a front end of the inlet pipe by which the impactor can be pulled while the striker is delivering impacts against the head in the same direction as a pulling force;
• and
• a valve in the inlet pipe which regulates supply of pressure fluid to the distributing mechanism.

A method for replacement of an underground pipe, comprising:

• inserting a cable through an existing pipeline from a first end to a second end thereof;
• connecting a free end of the cable extending from the second end of the pipeline to an impactor, which impactor includes a bursting head having a rearwardly opening recess, a striker mounted for sliding movement within the head, a distributing mechanism responsive to pressure fluid supplied through an inlet to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the head, and a pulling connection to which the cable is connected;
• pulling the impactor with the cable using a cable pulling system disposed at the first end of the pipeline, which cable pulling system pulls the cable in a plurality of repeated cyclic pulling strokes, including a holder that engages the cable and a cylinder having a movable piston operative to move the holder along the pulling stroke;
• operating the impactor to deliver impacts against the head in the same direction as the pulling force during a cyclic pulling stroke;
• and
• reducing operation of the impactor between cyclic pulling strokes so that the impactor does not substantially move between strokes.

A pneumatic impact mechanism, comprising:

• a tubular body having a rearwardly opening recess and a front end opening that communicates with the recess;
• an inlet pipe connectable at its front end to a source of pressure fluid and extending into the recess of the body through the front end opening;
• a striker mounted for sliding movement along the inlet pipe and an inside surface of the body for delivering forward impacts, the striker having a rearwardly opening recess and a front central opening of smaller diameter than the recess and which communicates with the recess, through which front opening the air inlet pipe extends;
• a distributing mechanism responsive to pressure fluid supplied through the inlet pipe to cause the striker to reciprocate in a cycle, which distributing mechanism includes
• a hole in the inlet pipe permitting pressure fluid from inside the inlet pipe to enter the rearwardly opening recess in the striker;
• a sleeve mounted at a rear of the inlet pipe in slidable, sealing relationship with a wall of the rearwardly opening recess in the striker, forming a pressure chamber for driving the striker forwardly;
• a first passage for permitting pressure fluid from the rear pressure chamber to enter a front pressure chamber ahead of the striker to move the striker rearwardly after an impact, which passage is isolated from the rear pressure chamber during a part of the striker cycle in which the striker is propelled forwardly;
• and
• a second passage for exhausting the front pressure chamber after the striker has moved rearwardly a sufficient distance.

A pneumatic impact mechanism, comprising:

• an elongated head including a tubular housing;
• a striker disposed for reciprocation within an internal chamber of the housing to impart impacts to a rear impact surface of the head for driving the impact mechanism forwardly through the ground;
• and
• an air distributing mechanism disposed for effecting reciprocation of the striker, including a sleeve slidably disposed in a rearwardly opening recess in the striker with the external surface of the sleeve separated from the rearwardly opening recess of the striker by a slight clearance, wherein an external surface of the sleeve has an annular groove therein with a seal bearing disposed in the groove, which seal bearing is oversized relative to the groove such that an annular space exists beneath the seal bearing at the bottom of the groove, and an outer portion of the seal bearing protrudes from the groove into sliding, sealing contact with the recess of the striker.

An impactor, comprising:

• a head having a rearwardly opening recess and a front end opening that communicates with the recess;
• an inlet pipe connectable at its front end to a pulling device and extending into the recess of the head through the front end opening, and having a pulling connection by which the impactor can be pulled while the striker is delivering impacts against the head in the same direction as a pulling force exerted by the pulling device;
• a striker mounted for sliding movement along the inlet pipe;
• a distributing mechanism which receives pressure fluid supplied through the inlet pipe to cause the striker to reciprocate in the rearwardly opening recess of the head to deliver forward impacts against the head;
• and
• a valve which regulates supply of pressure fluid to the distributing mechanism, including an enlarged diameter front portion of the inlet pipe which assumes a first position in response to pulling force exerted on the inlet pipe by the pulling device that causes the distributing mechanism to reciprocate the striker, and a second position in which relaxing of the pulling force on the inlet pipe causes the distributing mechanism to cease reciprocating the striker.