Deck-mounted control block for high-pressure hydraulic winches

Rexroth's control blocks for high-pressure hydraulic marine winches are entirely assembled from standard components. In other words, because they employ proven techniques and technologies, the system is highly reliable. All components are carefully documented, and parameters such as tightening torques are measured, evaluated and documented to keep the possibility of component failure to a minimum. And of course, standard components are cheaper than non-standard variants.

The modular design of the HICWB means it can be combined with virtually any winch. The vessel's owner can therefore hold fewer spare control blocks, providing more options when dealing with changes. These new Rexroth blocks can also be combined with both axial and radial piston motors, and with their light weight of just 44kg, they can even be directly motor-mounted.

In addition, each complete control block undergoes a specific treatment for resistance to extreme offshore conditions. The blocks themselves are galvanised and chrome-plated, and stainless steel is used for external moving parts such as the control lever and bushes. All adjustment elements have weatherproof covers. As a final protective barrier, a triple coating is applied in layers of 80micron thickness.

Besides the required standard functions like counter balance, relief and anti-cavitation valves, these lightweight and compact control blocks offer a range of additional features. First, they can proportionally control the winches or capstans used to raise or lower the anchor. The so-called anchor break off function of the block, in combination with a variable displacement motor, enables the anchor to be broken free in a controlled manner. A three-position hand lever valve is used for this function: in the break-off mode, up to 1.5 times the maximum rated load is permitted. The second position of the valve allows the operator to select minimum speed (which can be pre-set) at maximum rated load, followed by maximum speed with minimum load at the third valve position.

A second important feature of the control block lies in the ability to maintain a constant tension on the mooring lines when the vessel is berthed. When the mooring lines slacken due to vertical movement of the vessel, e.g. during tide, wave motion or loading/unloading, the winches will wind in to maintain line tension. When the lines are tightened by vertical movement in the opposite direction, then the winches will pay out line. The system's high responsiveness means that tension in the lines remains constant, avoiding overload and shock forces, and keeping the vessel firmly and securely moored against the quay.

Integrated safety features

Lastly, a number of safety features are integrated into Rexroth control blocks. An extreme situation can potentially occur when the hydraulic supply is cut to a winch holding a suspended load, and without a brake applied. Oil can then leak via the motor drain circuit back to the tank, resulting in insufficient hydraulic pressure to continue holding the load. Ultimately, the load will drop uncontrollably.

To ensure a safe situation even in cases such as this, an extra valve is incorporated to respond to falling pressure by holding the oil in the motor, and blocking leakage to the tank. The motor will slow down, but will not drop whilst the holding power remains assured.

Integrating these various features has made it possible to assemble a highly compact block. Not only does it require minimal space on deck, it also simplifies the integration of functionality in the installation, since it requires considerably less piping, and with fewer external couplings, the risk of leakage is even further reduced. This approach also drives down maintenance costs over the long term.

Finally, for all ship owners and builders there is the benefit of Bosch Rexroth's global service network, offering the capacity and expertise needed to quickly and efficiently service or repair marine installations anywhere in the world. Further information on Bosch Rexroth and the HIWCB control block can be found at www.boschrexroth.co.uk.