Boring or penetrating the earth – Boring without earth removal
Patent
1992-12-03
1994-06-07
Bui, Thuy M.
Boring or penetrating the earth
Boring without earth removal
E21B 400
Patent
active
053181352
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a soil displacement hammer with an improved reversing mechanism.
Soil displacement hammers, commonly referred to as "moles", are pneumatically operated, impact-action self-propelled mechanisms for driving holes in the ground. They can be used to install pipes, cables or conduits in the ground without the necessity for excavating a continuous trench.
GB-A-2,134,152 discloses a mole having a reversing mechanism. This mole comprises a cylindrical housing with an anvil member located at the forward end thereof. An impact piston is reciprocal in the housing to deliver successive impacts to the anvil member and forms with the housing a forward chamber cf variable volume. A control assembly comprises a forwardly extending sleeve which is slidably received within a rear space of the impact piston to form a rear chamber of variable volume. A central passage is connected to the sleeve for continuous supply of compressed air into the rear chamber and therefrom into the forward chamber through apertures in a side wall of the rear chamber of the impact piston. Means are provided for lockably locating the sleeve longitudinally with respect to the apertures for providing forward and reverse movement of the mechanism. These means include a pin which is engaged in a Z-shaped slot, and a helical spring which generally urges the control assembly into a forward position within the impact piston. This provides for normal forward movement of the mole. To provide reverse movement, the pin and slot mechanism enables the control assembly to be locked in a rearward location within the impact piston.
Another type of reversing mechanism for a mole is disclosed in GB-A-2,147,035. This is generally similar to the previous disclosure except that, instead of the pin and slot mechanism, the sleeve extending within the impact piston is movable to forward or rearward positions by means of screw threads on a rear extension thereof, which engage with corresponding screw threads of a locating member, whereby rotation of the sleeve causes longitudinal movement thereof.
An object of the present invention is to provide a simplified reversing mechanism for a mole which is more reliable in operation than the use of screw threads or pull/push (spring) methods as outlined above.
The present invention provides a pneumatically operated impact-action self-propelled mechanism for driving holes in the earth, comprising a cylindrical housing assembly with an anvil member located at a forward end thereof; an impact piston reciprocal in the housing to deliver successive impacts to the anvil member and forming with the housing a forward chamber of variable volume; and a control assembly comprising a forwardly extending sleeve which is slidably received within a rear space of said impact piston to form a rear chamber of variable volume, and a central passage within said sleeve for continuous supply of compressed air through a forward opening of the sleeve into said rear chamber and therefrom into said forward chamber through a port in a side wall of the rear chamber of said impact piston, characterised in that the sleeve has at least one aperture in its side near the forward opening and provided with valve means operable by twisting of the sleeve or a part thereof about its longitudinal axis, whereby when the aperture is closed by the valve means the compressed air is passed directly into the rear chamber for forward movement of the mechanism, and when the aperture is open compressed air can pass directly through said aperture and through said port into the forward chamber for reverse movement of the mechanism, and further characterised in that the sleeve has a circular collar remote from its forward opening and rotationally slidable inside a surrounding circumferential bush to define thereby two relatively sliding surfaces, one of said surfaces having one or more resilient protrusions adapted to locate temporarily in corresponding indentations in the other surface, whereby the sleeve can be located with the aperture open or closed by
REFERENCES:
patent: 4938297 (1990-07-01), Schmidt
patent: 5025868 (1991-06-01), Wentworth et al.
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