Editing Tower Bridge (section)

=== Hydraulic system===
[[File:Tower.bridge.99.machinery.london.arp.jpg|thumb|One of the original steam engines]]
The original raising mechanism was powered by pressurised water stored in six [[hydraulic accumulator]]s.<ref>{{cite web |url=http://www.towerbridge.org.uk/TBE/EN/BridgeHistory/ |title=Bridge History |website=Tower Bridge |publisher=[[City of London Corporation]] |date=1 February 2003 |access-date=13 June 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120620160843/http://www.towerbridge.org.uk/TBE/EN/BridgeHistory |archive-date=20 June 2012 }}</ref> 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|Tay Bridge Disaster]].<ref name=":5" />

The system was designed and installed by [[Hamilton Owen Rendel]] while working for [[Armstrong, Mitchell and Company]] of [[Newcastle upon Tyne]].<ref>{{cite news |title=Obituary – Hamilton de Marchi Owen Rendel |newspaper=The Times |date=19 September 1902 |page=8 |url=https://link.gale.com/apps/doc/CS135588659/TTDA?u=kccl&sid=bookmark-TTDA&xid=0fe40bc6 |access-date=24 June 2021 |url-access=subscription |archive-date=29 September 2024 |archive-url=https://web.archive.org/web/20240929053427/https://go.gale.com/ps/i.do?p=TTDA&u=kccl&id=GALE%7CCS135588659&v=2.1&it=r&sid=bookmark-TTDA&asid=0fe40bc6 |url-status=live }}</ref>{{sfn|Spencer-Silver|Stephens|2005|p=85}} Water at a pressure of {{cvt|750|psi|MPa}} was pumped into the accumulators by a pair of [[stationary steam engine]]s.{{sfn|Peacock|2011|p=24}} Each drove a force pump from its piston tail rod. The accumulators each comprise a {{convert|20|in|cm|adj=on}} ram which sits a very heavy weight to maintain the desired pressure.<ref name="phoenix" />

The entire hydraulic system along with the gas lighting system was installed by [[William Thomas Sugg|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.<ref>{{cite web |url=http://www.williamsugghistory.co.uk/ |title=History William Sugg & Co Westminster gas lighting cooking heating appliance manufacturer. |access-date=30 June 2013 |archive-date=30 June 2013 |archive-url=https://archive.today/20130630014442/http://www.williamsugghistory.co.uk/ |url-status=live }}</ref>

In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House.{{sfn|Peacock|2011|p=24}} 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 motor]]s and gearing. Oil is now used in place of water as the new [[hydraulic fluid]].{{sfn|Peacock|2011|p=25}}