1. Field of the Invention
The invention relates to a steerable ground drilling device, which comprises a body destined to be attached to a flexible pipe, a rotatable head which is mounted on the front extremity of the body and is provided with at least one spraying device to which fluid under pressure can be supplied through a pipe which extends through the head and the body and means for rotating the head.
2. Discussion of the Related Art
Such steerable ground drilling devices are especially utilized for making for tunnels in the ground into which the laying of so-called public utilities, such as cables and such and the like, is accomplished.
The steering of the ground drilling device can occur in various ways.
It is known to attach the head of the steerable ground drilling device to the body by means of a ball and socket joint, such that it can be fitted in relation to the body.
It is also known to provide the head with a guidable spraying device and to alter the spraying direction of the spraying device if required.
In yet another known ground drilling device the spraying device or a hammer drill is directed asymmetrically in relation to the axis of the body.
With continual rotation, the drilling device will move straight forward. With a stationary head the spraying is asymmetric and the drilling device will alter direction if it is pressed further rotatingly or hammered rotatingly.
With all these ground drilling devices the head must be stationary with alteration of direction.
Ground drilling devices are known whereby the head can rotating, even during the alteration of direction. In this way ground drilling devices are known whereby laterally directed spraying devices are provided in the body in order during the alteration of direction, to press the body away from the wall of the already formed opening.
All these known ground drilling devices are, however, relatively complicated and the steering of them is not easy.