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Lock Gates, Kings Dock Lock, Swansea
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There
are three pairs of lock gates installed in the Kings Dock Lock at
Swansea – the inner gates, the middle gates and the outer gates. The
middle and outer gates are identical in size, but the inner gates
are shorter in length to accommodate the inner cill of the lock. The
original lock gates were manufactured in 1907 by the Thames
Ironworks Shipbuilding & Engineering Co. Ltd. at a cost of £38,503
5s 0d., and the contract for the lock gate operating machinery was
awarded in the same year to Sir W G Armstrong, Whitworth & Co. Ltd.
in the sum of £4,250 0s 0d. There are also two reserve pairs of lock
gates, one for the inner position and the other for either the
middle or outer position. The reserve gates for the inner position
were manufactured in1928 by Vickers Engineering of Barrow in Furness,
and those for the middle/outer position by Fairfield Engineering of
Glasgow in 1947.
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Each lock gate
is essentially a steel tank divided into internal chambers by
horizontal and vertical bulkheads. The bottom chambers are normally
maintained dry, although a determined amount of water ballast is
added on occasions to increase the stability of the gate during
stormy weather conditions or very high tides. The upper chambers
have scupper openings which allow water to enter and exit the
structure as the lock is filled and lowered, so that the neutral
buoyancy of the gate can be maintained at all times. The level of
water in the lower chamber of each gate was initially controlled by
hydraulic ejectors, but in later years these were superseded by
electric pumps. Access to the various gate chambers is gained
through four “trunk” tubes – two short ones to the upper chambers
and two long ones to the bottom of the gate. These tubes were just
large enough for a man to traverse, and can clearly be seen in the
video below.
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Overall each lock gate
was manufactured to a high degree of accuracy and, to allow the gates to
make a good seal, the mitre, heel and cill - i.e. the outer edge, inner
edge and bottom - are finished with massive sections of precision-cut
greenheart timber. Each gate is hinged in position by a pintle and socket
at the bottom and a link plate, heel pin and "U" strap at the top.
Originally the mitre end was also supported by a large hinged roller which
ran along a purpose-built roller path at the bottom of the lock, and which
could be adjusted from above by a “spear rod” mechanism.
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When a gate required
major maintenance or repair it was released from its position by removing
any water from the lower chambers and blanking off the scupper openings,
thus sealing the gate and making it buoyant so that it could be floated
off its mountings. The replacement gate would then be brought into
position in a similar manner with the procedure reversed. Repairs were
carried out on a purpose-built slipway in the River Tawe – this being a
sloping ramp of approx. 30 degrees which was wide enough to accommodate a
pair of lock gates side by side. On the slipway were two robust
rail-mounted carriages which would be positioned at the bottom of the ramp
at low tide. At high tide the floating lock gate would be towed up-river,
positioned over one of the carriages, and allowed to settle as the tide
receded. It was then hauled to the top of the ramp, well clear of the
tidal reach, by air-operated winches and multi-purchase pulleys, and
finally jacked up onto the concrete support pillars mounted on the top end
of the slipway. The carriage could then be lowered away to allow access to
the underside of the gate (see photo of slipway, carriages and pillars
below).
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In this position,
major refurbishment work could be undertaken over an extended period.
Thorough cleaning, both internal and external, was followed by a detailed
inspection and the subsequent replacement of any internal structural
members that might have deteriorated over time. Damaged external plating
was repaired or replaced by the Boilermakers. The next step was to renew
the mitre, heel and cill timbers after these had been carefully prepared
in the Carpenters’ Workshop to very fine specifications. After checking
the overall dimensions, the gate would then receive several coats of
bitumastic paint, and replacement timber fenders would be fitted. Finally,
all access manholes and scuppers would be blanked off, an air compressor
attached, and the gate would be pressure-tested for leaks. Job done!
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Full credit must be
given to the Edwardian engineers responsible for the design and
construction of the lock gates and operating machinery, and of the lock
structure itself which was built with materials such as granite worked to
a high degree of accuracy, and without the use of modern-day lifting and
cutting machinery.
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View of installation
of outer lock gates
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The finished lock - view
from the sea and ready for shipping - showing swing bridge that
gave access to Queens Dock and Palmers Dry Dock.
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Maintenance fitters
''repacking'' the hydraulic piston that operated the lock gates.
This was a regular job that had
to be completed between the ''tides'' at low water when the lock was
inoperative, whatever the weather.
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Floating lock gate
being towed away by tugs from the lock after removal.
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View of Slipway and carriages
used for the maintenance of the lock gates
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The water hydraulic
system was replaced by oil hydraulic and electrical control in the
late 1990s |
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Photo showing new lock
gate control room
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