As mentioned
elsewhere, yesterday myself and a small and privileged group from Southwark Cyclists went to see this
only from the inside, and underneath, and in the areas behind the electrified fence, not normally open to Joe Public.
This is one of the smaller ‘falling’ gates, of which there are four, each one spanning 31.5 metres between the piers. Those (like this one) closest to the banks are non-navigable.
Beneath the river, in the concrete trough where the gates sit when they are not in use, there are two service tunnels – one on the upriver side, one on the down river side.
The tunnels are similar in size to the inside of a tube train and carry masses of wiring and fire protection between the piers. All power and other services are duplicated in the second tunnel as back-up. They are painted in a pale green colour, as favoured at one time by government institutions.
It is possible to access one bank of the river from the other using the tunnels. When I mentioned this to Simon L3, I he (unsurprisingly) thought I'd come up with a new FNRttC river crossing point.
The yellow lump towards the left side of this picture, is the indoors end of one of the yellow
A-frames (pictured below) which can be seen on each of the larger piers. The yellow cylinder on the right is one of two which contain pistons which push or pull the A-frame which in turn rotate the gate.
Each of the large gates weighs 3700 tonnes and closes off a 61m span of the river.
Each gate, apparently, contains more steel than the Eiffel tower.
The span is identical to that of the piers of Tower Bridge. Each gate can withstand a force of 9000 tonnes.
This is the business end of the piston with it’s ram in a protective gaiter.
15,000 tones of pressure is what it can dish out.
Although each gate has an A-frame with two pistons on each side, only one side is used to power the gate up or down, the hydraulics on the other side idle while it does so. At the time of construction, the technology didn’t exist to synchronise the hydraulics on both sides and it was feared the gates might twist. The duplicated hydraulics also act as a back-up in the event of a failure of one side. There is also a third means by which the gates can be rotated in the event of both sets of hydraulics failing.
This is one of the bolts which retains the cover on the back of the cylinder. I reckon it’ll take an M75 (or thereabouts) Allen key. As well as A Lot Of Wellie to undo it.
Each piston has it’s own 190hp electric motor to pump up the hydraulic oil to pressure.
Yes we did work in pound/feet per square inch, not that long ago
What’s in here, I wonder?
Porthole and navigation lights
Somewhat surprisingly, the construction of the top half of each of the piers is wooden (iroko from Africa for the beams, with boards of European pine) and then clad with thin sheets of stainless steel.
Lots of clunky switchgear everywhere.
Rust, as they say, never sleeps.
This is in 2m thick concrete, under the river.
In all a fascinating day out, with my thanks to Ed our informative guide from the Environment Agency, and to Barry Mason for arranging it all.
