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Hydraulic System

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Tower Bridge Hydraulic System

The original raising mechanism was powered by pressurised water stored in six hydraulic accumulators.

The system was designed and installed by Sir W. G. Armstrong Mitchell & Company of Gateshead. Water, at a pressure of 750psi was pumped into the accumulators by two stationary steam engines, each driving a force pump from its piston tail rod. The accumulators each comprise a 20-inch ram on which sits a very heavy weight to maintain the desired pressure.

In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House. The only components of the original system still in use are the final pinions, which engage with the racks fitted to the bascules. These are driven by modern hydraulic motors and gearing, using oil rather than water as the hydraulic fluid.

Some of the original hydraulic machinery has been retained, although no longer in use. It is open to the public and forms the basis for the bridge's museum, which resides in the old engine rooms on the south side of the bridge. The museum includes the steam engines, two of the accumulators and one of the hydraulic engines that moved the bascules, along with other related artefacts.

 The third steam engine During World War II, as a precaution against the existing engines being damaged by enemy action, a third engine was installed in 1942. This was a 150hp horizontal cross-compound engine built by Vickers Armstrong Ltd., at their Elswick works in Newcastle-upon-Tyne. It was fitted with a 9 feet diameter flywheel weighing 9 tons, and was governed to a speed of 30 rpm.

The engine became redundant when the rest of the system was modernised in 1974, and was donated to the Forncett Industrial Steam Museum by the Corporation of the City of London.



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