Volume Twelve - Pre-Victorian to the Present Day - further aspects - 1898 - A Clever Piece of Engineering . . .

To get at the bottom of the gates and the roller paths, which of course is the lowest part of the work, the following plan was followed. The tide did not ebb sufficiently low for any length of time to enable the work to be done without keeping back the water, and, therefore, a pair of shallow timber dams, packed intermedially with clay, were constructed and fixed down, being held in position by lugs and bolts attached to the walls on either side. These are shown in Figs. 1, 2, and 3.

There was also a movable shoot to take away drained-in water by means of centrifugal pumping engines at the bottom of the dock, as shown. The gates to be operated upon were thus between two dwarf dams. One dam was on the apron on the inside, and was 6 ft. high, and those placed on top of stone sills were 2ft. 6in. Their height gave 34 hours’ work per tide before the dams were overflowed.

As soon as the tide ebbed clear of the top of the dam pumping was commenced, and it took 16 to 18 minutes to clear the space of water. Work went on tide after tide night and day until the operations were finished, it taking about three months to complete both pairs of gates.

The work consisted of taking out the old timber sills and putting in new greenheart, and also changing the sluices and frames, the wing rollers, and the carrying rollers on the points of the gates. Defective rivets and bolts at the bottom of the gates were also replaced.

Figs. 4 and 5 show in enlarged detail the ends of the holding-down blocks, the former being a section ;

Figs. 6 and 7 show respectively a sectional elevation and a half-plan of the pump suction.

Fig. 8 shows pipe connections.

Figs. 9 and 10 show the arrangements for repairing or renewing the bottom guide rollers, under which the chains for opening the gates passed. It will be seen that the bottom opening of the chain race is closed by a cover made tight by a felt grummet.

Figs. 11 and 12 show enlarged details.