Method and system for operating a reversible pneumatic ground piercing tool
View Patent ↗A method of the invention uses a pneumatic ground piercing tool having a reversing mechanism with a supplemental air line capable of supplying compressed air for reverse operation to a radial port in the air distributing mechanism. This radial port is located between a pair of bearing surfaces on the step of the air inlet conduit, and when pressurized by the supplemental air line, causes the front pressure chamber to receive compressed air earlier than normal, shifting the stroke of the striker rearwardly so that the tool operates in reverse. Such a method includes the steps of operating the tool in forward mode by supplying compressed air to the first air hose, and operating the tool in reverse mode by supplying compressed air to the second air hose while permitting partial venting of the front pressure chamber through the first air hose.
1. A method of operating a reversible pneumatic ground piercing tool of the type including
an elongated tool body having a rear opening and a front nose including an anvil,
a striker disposed for reciprocation within an internal chamber of the housing to impart impacts to a rear impact surface of the anvil for driving the tool forwardly through the ground, the striker having a rear bearing in sealed, sliding engagement with an inner wall of the tool body,
an air distributing mechanism for effecting reciprocation of the striker, including a rearwardly-opening recess in the striker having a radial air flow port extending through a wall of the recess, a stepped air inlet slidably disposed in the recess in sealed engagement with the recess wall, the stepped air inlet having a front external edge, a rear external edge, a first air flow passage extending through the air inlet from rear to front in a lengthwise direction, and a first air hose connected to the first air flow passage for supplying compressed air to the recess to push the striker forwardly until the radial port in the recess wall passes the front edge of the stepped air inlet, at which time compressed air enters a front pressure chamber ahead of the rear seal bearing of the striker thereby beginning a rearward stroke of the striker, travel of the striker continuing rearwardly until the radial port in the recess wall passes over the rear edge of the stepped air inlet, thereby depressurizing the front pressure chamber,
a tail assembly mounted in a rear end opening of the housing that secures the striker and air distributing mechanism in the housing and which receives rearward impacts from the striker when the tool is operating in reverse, and
a reversing mechanism including a second air flow passage extending from the rear of the stepped air inlet to a radial port on an exterior surface of the stepped air inlet between the front and rear external edges thereof, and a second air hose connected to the second air flow passage for supplying compressed air to the radial port in the stepped air inlet to pressurize the front pressure chamber when the radial port in the recess wall moves over the radial port in the stepped air inlet, thereby beginning a rearward striker stroke sooner than if no compressed air is supplied to the radial port of the stepped air inlet,
wherein the method comprises the steps of:
operating the tool in forward mode by supplying compressed air to the first air hose; and
operating the tool in reverse mode by supplying compressed air to the second air hose while permitting partial venting of the front pressure chamber through the first air hose.
2. The method of claim 1 , wherein the second air hose, second flow passage and radial port on the exterior surface of the stepped air inlet remain sealed during forward mode operation by closing a valve disposed between the second air hose and an air compressor that feeds compressed air to the second air hose.
3. The method of claim 2 , wherein partial venting is accomplished by
opening a valve that permits the interior of the first air hose to communicate with the atmosphere through a vent; and
feeding vented air flowing from the front pressure chamber flowing through the first air hose through an orifice having a reduced diameter relative to the inner diameter of the first air hose, thereby limiting the rate at which air can escape through the vent.
4. The method of claim 1 , wherein partial venting is accomplished by
opening a valve that permits the interior of the first air hose to communicate with the atmosphere through a vent; and
feeding vented air flowing from the front pressure chamber through the first air hose through an orifice having a reduced diameter relative the inner diameter of the first air hose, thereby limiting the rate at which air can escape through the vent.
5. An apparatus for operating a reversible pneumatic ground piercing tool of the type including
an elongated tool body having a rear opening and a front nose including an anvil,
a striker disposed for reciprocation within an internal chamber of the housing to impart impacts to a rear impact surface of the anvil for driving the tool forwardly through the ground, the striker having a rear bearing in sealed, sliding engagement with an inner wall of the tool body,
an air distributing mechanism for effecting reciprocation of the striker, including a rearwardly-opening recess in the striker having a radial air flow port extending through a wall of the recess, a stepped air inlet slidably disposed in the recess in sealed engagement with the recess wall, the stepped air inlet having a front external edge, a rear external edge, a first air flow passage extending through the air inlet from rear to front in a lengthwise direction, and a first air hose connected to the first air flow passage for supplying compressed air to the recess to push the striker forwardly until the radial port in the recess wall passes the front edge of the stepped air inlet, at which time compressed air enters a front pressure chamber ahead of the rear seal bearing of the striker thereby beginning a rearward stroke of the striker, travel of the striker continuing rearwardly until the radial port in the recess wall passes over the rear edge of the stepped air inlet, thereby depressurizing the front pressure chamber,
a tail assembly mounted in a rear end opening of the housing that secures the striker and air distributing mechanism in the housing and which receives rearward impacts from the striker when the tool is operating in reverse, and
a reversing mechanism including a second air flow passage extending from the rear of the stepped air inlet to a radial port on an exterior surface of the stepped air inlet between the front and rear external edges thereof, and a second air hose connected to the second air flow passage for supplying compressed air to the radial port in the stepped air inlet to pressurize the front pressure chamber when the radial port in the recess wall moves over the radial port in the stepped air inlet, thereby beginning a rearward striker stroke sooner than if no compressed air is supplied to the radial port of the stepped air inlet,
which apparatus comprises:
means for operating the tool in forward mode by supplying compressed air to the first air hose; and
means for operating the tool in reverse mode by supplying compressed air to the second air hose while permitting partial venting of the front pressure chamber through the first air hose.