CO129-459 - Individuals - 1919 — Page 270

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JAFFÉ ON HONG KONG WATERWORKS,

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Two additional sets of pumping-plant have been installed in connection with the Taitam Tuk reservoir, each capable of lifting 3 million gallons in 24 hours to a maximum height of 387 feet. The pump-lift will, however, vary from 287 feet to 387 feet, exclusive of friction in the mains, there being a difference of 100 feet between the lowest draw-off of the Taitam Tuk reservoir and the level of the overflow crest. The lowest draw-off is 4 feet below the level of the engine-house floor.

These engines are triple-expansion, vertical, having high-pressure cylinders 18 inches, intermediate 31 inches, and low-pressure 50 inches in diameter, the stroke is 36 inches and the revolutions 30 per minute. The pumps, three to each engine, have 153-inch diameter rams driven direct from the cross-heads by four side rods directly connected. The boilers, three in number, are of the Lancashire type, and are fitted with superheaters, and there is an economizer in connection with the main flue; the boiler-pressure is 150 lbs. per square inch.

The total pumping-capacity of the station is now 8 million gallons per day. As the present requirement of full supply is 5 to 5 million gallons per day, the combined plant is sufficient to maintain the full service with either the two old engines or one of the new engines in reserve.

ROADS AND MAINS.

The laying of a main from the pumping-station to the inlet of the tunnel for the gravitation supply entailed the construction of an entirely new road; but for the main from the Intermediate reservoir to the station an existing road which led down the valley was utilized. It was, however, necessary to extend it along the foreshore from the head of Taitam Bay to the pumping-station. The existing road could not have been used for the pumping-main because it was within the area which would be submerged when the Taitam Tuk reservoir was filled. For the supply main from the Intermediate reservoir this did not matter, because this was to be taken up and relaid for further service in connection with the Taitam Tuk reservoir. The new road to the tunnel inlet is 3,430 yards in length. As the greater portion of the road was intended for public traffic, and had also to accommodate three 18-inch diameter mains, it was made 20 feet in width. Where it was intended for the mains only the width was 12 feet. The road for a continuous length of 1,689 yards is of a uniform gradient of 1 in 250 but for the remainder it ranges from 1 in 50 to 1 in 8.

Papers.] LOW-LEVEL RESERVOIRS AND WORKS FOR PUMPING. 19

In addition to many heavy cuttings and retaining-walls, four bridges were required, the largest of which consisted of three spans of 50 feet each, the height from ground-level to the crown of the central arch being 85 feet. The bridges are all granite-faced concrete structures.

The extension of the existing road along the foreshore of Taitam Bay for the supply main from the Intermediate reservoir to the pumping-station was all light work. After being shortened and straightened by the construction of an embankment, 358 yards in length, it now serves for the accommodation of the two supply mains from the Taitam Tuk reservoir, As the foreshore on which the embankment is formed was soft, piers on pile foundations were built within the embankment, at intervals of 12 feet, for the support of the mains. The embankment is pitched throughout with coursed granite dry rubble springing from a pell-mell rubble toe.

Both pumping- and supply-mains are 18 inches in diameter, formed of cast-iron spigot-and-socket pipes inch in thickness and 12 feet in length. Very few curves of smaller radius than could be got round with the play in the joints of the pipes were necessary; but, where they occurred, angle collars were used. Each pumping- main is divided into three sections by two reflux-valves of the multiple-flap type. These valves are placed in brick chambers below road-level. In addition to the reflux-valve, a sluice-valve, air-valve, wash-out and a by-pass for the reflux-valve is provided for each main at these places. Additional wash-out and air-valves are provided at intervals along the pumping- and supply-mains. The pumping-mains are 3,430 yards in length from the pumping- station to the inlet of the tunnel and the supply-mains from the Taitam Tuk dam to the pumping-station are 900 yards in length. All three pumping-mains are now being pumped through, but two are of sufficient capacity to convey the present full supply to the city in the event of the third main requiring repairs.

INTERMEDIATE RESERVOIR.

The Intermediate reservoir, which was constructed in 1904-7 in connection with the first section of the Taitam Tuk works, bas a capacity of 210 million gallons. This reservoir now only supple- ments the Taitam Tuk reservoir, as its contents can no longer be pumped separately, but must be drawn off by the standpipe in the valve-tower of the dam and allowed to flow down the stream-course

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