Boring or penetrating the earth – Below-ground impact members – Fluid-operated
Patent
1994-02-14
1995-05-09
Buiz, Michael Powell
Boring or penetrating the earth
Below-ground impact members
Fluid-operated
F21B 414
Patent
active
054131855
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a soil displacement hammer with a movable head.
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. Moles of this kind are described in GB-A-2 134 152 and GB-A-2 147 035.
Moles have been proposed with moving heads to assist in breaking the soil at the front of the mole. Examples of such moving heads are shown in GB-A-1 392 868 and GB-A-2 111 565. The heads in these moles are powered by the main piston striking the back of the head, the head then travelling forward and being returned by means of a spring. Although it is intended that this reciprocal action continues as the mole progresses through the ground, there are practical difficulties. The force of the surrounding soil tends to hold the head in the forward position, so that the mole once again becomes a fixed head machine. If the spring is made sufficiently strong to return the head against the force of the soil, then it would be far too strong to allow the piston to move the head forward in the first place.
The present invention overcomes the above problems by having the head powered by compressed air, ideally from the same source as the compressed air which powers the main piston.
Thus, 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; a pneumatically-operated 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; characterised by a head chamber forward of the anvil member, a head piston reciprocal in the head chamber and connected at its forward end to the head of the mechanism, and compressed air supply means communicating between the forward chamber and the head chamber to the rear of the head piston so as to cause the head piston to travel forwards.
In a preferred embodiment, the air supply means is a forwardly extending sleeve which is slidably received within a rear space of the head piston. The head piston includes a front interrupted shoulder and a rear continuous shoulder in sliding contact with the internal walls of the forward chamber, and an air port is provided between these two shoulders and communicating between the rear space of the head piston and the head chamber forward of the head piston. When the head piston is in its rearward position, compressed air passes into the rear space and causes the head attached to the piston to move forwards. When the front shoulder of the head piston has moved forward past the outlet of the air supply means, compressed air can escape through the air port into the space in the head chamber in front of the rear shoulder of the head piston. This causes the head piston to move backwards, with the air being exhausted through an exhaust hole communicating between the head chamber and the forward chamber of the main body of the mechanism.
Reference is now made to the accompanying drawings, in which:
FIG. 1 is a diagrammatic sectional view of a mole according to a preferred embodiment of the invention;
FIG. 2 is a detailed view of elements in the front section of the mole with the head piston in the rearward position;
FIG. 3 is a view corresponding to FIG. 2 with the head piston removed for clarity;
FIG. 4 is a view corresponding to FIG. 1 of a modification in which the return of the head is assisted by a spring; and
FIG. 5 is a view of a further modification in which the return of the head is assisted by a rubber bush.
Referring to FIG. 1, the main conventional elements of the mole will first be described, these being substantially similar to those of GB-A-2 134 152 and GB-A-2 147 035. The mechanism comprises a cylindrical housing 1 having an anvil 2 located internally at the for
REFERENCES:
patent: 4964477 (1990-10-01), Tupitsyn et al.
patent: 5193627 (1993-03-01), Jenne
patent: 5318140 (1994-06-01), Ekwall et al.
Buiz Michael Powell
Powermole International Ltd.
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