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The " Hydraulic Lift Dock " consists of a platform, formed by 

 pontoons connected to a row of pillars or hydraulic presses on each side. 

 When a vessel requires to be docked, valves are opened to admit the 

 water into the pontoons so that the platform may sink to the required 

 depth, the vessel is then hauled over it and shored. The platform and 

 vessel are then lifted by means of the hydraulic presses on each side ; 

 at the same time the water is allowed to escape from the pontoons 

 whicii are then sufficiently buoyant to support the vessel above water. 



The " Floating Dock " consists of a hugh iron pontoon formed like 

 an ordinary Graving Dock ; when required for use, valves are opened to 

 admit the water, and the structure gradually sinks to the required depth 

 to receive the vessel, which is floated into it and shored. The water is 

 then pumped out by steam power until the floor of the dock is above 

 water ; it can then be moved to any suitable position. For general 

 purposes it is evident that the ordinary Graving Dock has the advantage 

 of all these systems, the vessel when once inside and shored in the dry is 

 free from accident and the risks attending mechanical complications ; 

 moreover, the vessel is uniformly accessible both for workmen and 

 materials at all times, being in no way aflected by the rise and fall 

 of the tide. 



Hydraulic machinery is now extensively used in connection with 

 docks, for the working of cranes, opening and closing the gates, turning 

 swing-bridges and capstains. The pressure is obtained by load instead of 

 by elevation, and is generally that due to a head of water 1,500 feet high, 

 or about 700 lbs. per scjuare inch. This is produced by means 

 of pumping by steam power against a column of water supporting 

 a loaded piston termed an accumulator. The water pressure is 

 transmitted from the accumulator to the several machines around 

 the docks, by means of pipes laid under the surface of the 

 quays, and the ej;haust water is sometimes brought back in return pipes to 

 the pump-well and used over again. 



On the Mersey Dock Estate hydraulic machinery is very extensively 

 employed, and the arrangements carried out in connection with the ware- 



