System for controlled lowering of a tube or cable

DETAILED DESCRIPTION The object of the invention is now to eliminate the above indicated disadvantage.
In agreement with said object the invention now provides a system of the above indicated type which according to the invention is characterized in that the fluid inside each inflatable body has a specific weight equal to or at least nearly to the specific weight of the surrounding water.
It is especially preferred that the fluid inside each inflatable body consists of the same water as the surrounding water.
In one further development each valve unit is connected to a separate fluid reservoir attached to the corresponding braking unit and acting as source of pressurized fluid for said valve unit.
Each braking unit is now able to operate independent of the others.
The large number of reservoirs could be a disadvantage of this embodiment.
In another development a number of valve units (preferably all valve units) are connected to a fluid conduit which extends along the tubular guide and is connected to one fluid reservoir acting as source of pressurized fluid for said valve units.
Only one reservoir is needed in this embodiment, however, a fluid conduit is necessary between each valve unit and the common reservoir.
The control communication between the control center and the valve units can be performed in various ways using data transfer along electrical connections, along acoustical communication paths, using radio waves, etc.
In all known prior ad cases pressurised air is used as fluid for inflating or deflating the inflatable bodies of the braking units and for determining in correspondence therewith the applied braking force.
Assume a water depth of 2000 m and assume a desired control range of 50 cm water column.
In that case 4000 braking units would be necessary each capable of functioning at a different depth and at a different hydrostatic bias pressure.
With increasing water depth the controllability of the valve units becomes more and more a problem.
The valve unit which has to operate for instance at 1000 m depth should have a pressure control range between 999