Bosch Rexroth (represented locally by Tectra Automation) has supplied its electro-pneumatic pressure control valve technology to Vosta LMG which specialises in the customisation of freighters.
This technology has been deployed by Vosta in the Chinese Harbour Engineering Company's (CHEC) fleet of dredgers in Shanghai Harbour. Shanghai is booming and as a result, more harbours and shipping lanes capable of dealing with overseas traffic are needed. The Vosta dredging technology enables the fleet to move enough sand to create artificial islands. It can 'vacuum free' shipping lanes for ships with a draught of up to 18 metres. The electro-pneumatic pressure control valves provided by Rexroth, control the pressure compensation of the transmissions.
CHEC maintains a fleet of more than 800 modern work vessels such as dredgers, pontoon cranes and container barges. These vessels distinguish themselves by their high speeds, high capacity and their ability to dredge depths of up to 60 metres. The latest addition to the fleet is a dredger being used in Shanghai, whose hull can take on 13 000 m³ of sand and water.
Sucking up the sand-water-mix from beneath the surface of the water is not without its problems. If water or sand gets into the transmission, work will grind to a halt. This can easily happen as the deeper the dredging, the higher the water pressure becomes. The pressure needs to be compensated for and a specific pressure differential between the transmission chambers is necessary, making maximum reliability absolutely essential. This makes the electro-pneumatic pressure control valves by Rexroth a suitable choice for Vosta.
A 2,1 MW electric motor drives the transmission and the underwater pump. The dredging process sparks a race, as the pressure inside the transmission must always be higher than the pressure outside. This again depends on the water depth at which the suction pipe is operating. In order to ensure this difference in pressure, a bypass valve actuates an air volume sensor between the pressure control valve and the transmission volume once a pre-determined water depth is attained. In the event of a leak, the pressure control valve will initially maintain the pressure in the transmission chambers while the air volume sensors monitor the leak. The amount of air flowing through is an indicator of the size of the leak. A diagnostic system, which sorts and displays the data, is integrated into the control unit. This allows operators of the dredger to take preventive measures in good time.
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