Telescopic boom arm

1. A telescopic boom arm operable between a retracted position and an extended position, the telescopic boom arm comprising:

an elongate first boom section comprising top and bottom walls and opposed side walls, the walls defining a first cross section;

an elongate second boom section comprising top and bottom walls and opposed side walls, the walls of the second boom section defining a second cross section, which is smaller than the first cross section, and being dimensioned such that an elongate channel is formed between the bottom walls of the first and second boom sections, the elongate channel having an enclosed length variable by extension and retraction of the second boom section relative to the first boom section, the enclosed length being maximized with the second section is fully retracted and minimized with the second section is fully extended;

at least one partition wall secured to the bottom wall of the first boom section and extending generally perpendicular therefrom toward the bottom wall of the second boom section, the at least one partition wall further extending substantially the length of the elongate channel between the first and second boom sections for dividing the elongate channel into a plurality of separate longitudinal channels, each separate longitudinal channel having sufficient width to receive only two flexible hydraulic lines;

a third boom section and a fourth boom section and a plurality of hydraulic double-acting cylinders mounted on the third boom section, one cylinder including a piston rod connected to the second boom section and the other cylinder including a piston rod connected to the fourth boom section, the second boom section being moved relative to the first boom section by means of a double-acting cylinder affixed to an outer surface of the top wall of the first boom section; and

a first plurality of elongate flexible hydraulic lines, each line of said first plurality being connected via a connector at one end to the bottom wall of the first boom section and partially disposed within the elongate channel, two lines in each longitudinal channel, when the boom arm is in its retracted position, each line being connected at the other end to in respective pairs to the double acting hydraulic cylindrs in the third boom section such that each line comprises two runs separated by a U-bend, one of the two runs being partially disposed in the longitudinal channel, and wherein respective lengths of the two runs varies inversely as the telescopic boom is extended or retracted thereby causing the position of the U-bend to move, as the telescopic boom is moving, along the length of the longitudinal channel at a rate generally equal to a rate of change in the enclosed length.

2. A boom arm according to claim 1 , wherein the hydraulic cylinders are fluidly connected in series, whereby the boom sections are moved simultaneously by the hydraulic cylinders.

3. A boom arm as claimed in claim 1 , further comprising a plurality of rigid tubes, each connected at one end to a respective one line of the first plurality of flexible hydraulic lines and at its other end to a respective end of a second plurality of flexible lines leading to a distal end of the fourth boom section for powering an implement or device carried by the boom arm.

4. A boom arm according to claim 3 , wherein the second plurality of flexible lines connected to the front end of each rigid tube comprises two runs separated by a U-bend disposed within the fourth boom section.

5. A boom arm as claimed in claim 4 , wherein one of the two runs of each of the second plurality of hydraulic lines is disposed within a closed channel defined by the fourth boom section.

6. A boom arm as claimed in claim 5 , wherein the closed channel comprises a strip of L-shaped cross section inside the corner of the fourth boom section.