Sessional_Paper_1902 — Page 722

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The draw-off

valves.

Venturi meters to tilter-beds.

Large Venturi meter for registering daily con- sumption.

Measure-

10. I am of opinion that it will be advisable to reduce the diameter of the out- let valves in the tower to 6", providing proper taper-pieces for connection with them. With suitably-formed taper-pieces the delivery will not be appreciably reduced, and the smaller valves will be much easier to open and shut, than the large, and much less liable to breakage, in so doing. Some arrangement for closing the outlets, outside the tower, in the event of breakage, should be provided. These matters can be arranged, when the indent for the iron-work is sent in.

11. The drawings of the filter-beds have not yet been completed. If they are designed, on the lines of those now in use in Hongkong, they will answer well. I recommend however that each filter-bed be provided with a separate Venturi- meter constructed in accordance with a special arrangement, adapted for the regula- tion of filtration. On my return to England I will be happy to obtain a quotation for these meters.

12. It would also be well to provide one large recording Venturi meter, for registering the daily consumption of water from the service-reservoir.

13. It is desirable to measure the flow of the streams close below the reservoir, ment of flow during construction. The arrangements should be such as to admit of accurate measurement, not only of dry weather flow, but also of moderate floods.

of streams

during con-

struction.

Construction

of service- reservoir.

Subsidiary filter-beds.

Probably the best arrangement would be one similar to that suggested for the measurement of the flow of Taitam stream; a large V notch for measuring small flows, and a wide square notch, for floods. It will be well also to have a self- recording water-level indicator, at each gauge.

14. The service-reservoir drawings are not yet complete. It is very properly to be roofed. I have recently used roofs composed of concrete on steel girders and joists supported by cast iron stanchions, an arrangement which has usually proved more economical than masonry arches and piers. Whether this would be the case, in the present instance, I cannot say. It would however be well to get out alter- native designs for the two classes of roofs. The proposed circular form lends itself to the site and naturally has the shortest length of wall, for a given capacity. I must however state that, owing to the difficulty in devising an economical cover- ing, I have rarely found circular reservoirs economical in first cost.

15. The principal filter-beds are to be placed near to the reservoir.

It is proposed to intercept certain streams along the pipe track, between the filter-beds and the service-reservoir, and at each intake to construct a small filter-bed to filter the water of the stream, prior to its admission to the main.

I suggest the use of the Fischer Artificial Filter for these subsidiary beds. This filter consists of flattened bottles, made of porous material, composed of sand and glass, fused together. Each bottle is rectangular 3′ 3′′ × 3′ 3" x 4". These are placed upright, in a suitable tank. A large filtering-area is provided, with relatively small floor-space. The water surrounds the filter-plate and passes through its pores, to the interior cavity, whence it is drawn off by appropriate pipes. The main advantage of the Fischer Filter, in the present case, is the ease with which it can be cleaned, and managed. A small cistern is provided at an elevation of about 10 feet, into which filtered water is pumped. The cleaning of the filter is accomplished, merely by altering the adjustment of certain valves so as to reverse the direction of the flow through the filtering material. The filtered water enters the interior cavity, passes out through the pores of the material, and forces off the adhering slime, which is then sludged out of the filtering-chamber. I have experimented on one of these filters, in connection with some very dirty water, and found that it could be cleaned with the utmost ease. I do not assert that the Fischer Filter effects better, even as good, results as well-managed sand-filtration, but I am confident that it will give better results than an ill-managed sand-filter. I fear that it will be both expensive and difficult to secure good management, in the case of small scattered filters.

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