There are three pairs of lock gates installed in the Kings Dock Lock at Swansea – the outer gates numbered 1 and 6, the middle numbered 2 and 5, and the inner numbered 3 and 4. The outer and middle gates are identical in size, but the inner gates are shorter in height to accommodate the higher inner cill. 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.
Each lock gate is essentially a steel tank divided into four 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 on the outer face 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water in the lower chamber of each gate was initially controlled by hydraulic ejectors, but in later years these were superseded by electric pumps.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.
Overall each lock gate was manufactured to a high degree of accuracy to allow each gate to marry up to it’s partner and make a good seal at the mitre, heel and cill. The outer edge, inner edge and bottom of each gate are finished with substantial sections of precision cut greenheart timber. Each gate is hinged in position by a pintle and socket at the bottom and a "U" strap at the top. The mitre end of each gate is 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. The gates were operated by a water hydraulic driven piston, operating at 800 psi, which connected via a guided crosshead and box girder to the “crocodile” girder which was secured to the top of the gate and hinged to a link plate directly above the “U” strap supporting the gate.
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 after disconnecting the operating gear. 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 by tugboat from the dock up-river and 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 from the carriage and lowered onto 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).
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!
Full credit must be given to the Edwardian engineers responsible for the design and construction of the lock gates the operating machinery, and of the lock structure itself which was built with materials such as granite worked to a high degree of accuracy and finish without the aid of modern day lifting and cutting machinery.