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Hydraulic system

The original raising mechanism was powered by pressurised water stored in six hydraulic accumulators. There were then two pairs of engines on each pier. Each pair consisted of a larger engine 8 ½ inches in diameter and a smaller one at 7 ½ inches. All eight engines had three cylinders. The reason for two pairs of engines on each pier was to build in redundancy. The machinery was "equal to twice the requirements of the Board of Trade", already very rigorous standards established following the Tay Bridge Disaster.

The system was designed and installed by Hamilton Owen Rendel while working for Armstrong, Mitchell and Company of Newcastle upon Tyne. Water at a pressure of 750 psi (5.2 MPa) was pumped into the accumulators by a pair of stationary steam engines. Each drove a force pump from its piston tail rod. The accumulators each comprise a 20-inch (51 cm) ram which sits a very heavy weight to maintain the desired pressure.

The entire hydraulic system along with the gas lighting system was installed by William Sugg & Co Ltd. The gas lighting was initially by open-flame burners within the lanterns, but was soon updated to the later incandescent system.

In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House. The only remaining parts of the old system are the final pinions, which fit into the racks on the bascules and were driven by hydraulic motors and gearing. Oil is now used in place of water as the new hydraulic fluid.