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Due to the variety of sources and different duties required the stations differ widely in their layout and capacities. The details are set out in Table No. 7, the stations being classified according as they pump raw or filtered water. It will be observed that the early instal- lations were either steam or water turbine driven pumps, later electrical power was used and now diesel engines are being installed. Table No. 8 shows one reason for this trend in the expense of fuel for the steam engines. A change to oil firing had been con- templated at both Tytam Tuk and Pokfulam Road, but recent boiler surveys have shown that the boilers should be scrapped, and the main worry now is whether they can be made to last out until new plant can be delivered. A complete turn over to Diesel Power for regular use at Pokfulam Road is already on order but one steam set will be maintained for standby duties. During the occupation when coal became scarce, the Japanese brought up a large electric motor from the Hong Kong and Shanghai Bank and coupled it by a belt drive onto the flywheel of the steam engine. During the Japanese occupation also the pumping station at Garden Road was completely stripped and the whereabouts of the pumps has never been discovered. Replace- ments have now been installed, being a duplicate order on the original suppliers. Similarly the three pumps at Albany had also been removed, but one was found near the summit of Tai Mo Shan where the Japanese had established a radar station with its own power plant and water supply. This one was recovered and re-installed in 1946, but the other two had to be replaced from the United Kingdom.
The number of small pumping stations is unfortunately necessary by the nature of the distribution difficulties. Whilst admittedly giving greater flexibility, with increased wages it is becoming increasingly expensive and some greater degree of centralisation is required. A step in the right direction is being made at Eastern where in conjunc- tion with a centralisation of filtration plant a single pumping station will house eight pumps for three separate duties.
The location of the Tytam trunk main at Bowen Road level has rendered possible the use of water power for pumping. This is so from the fact that the amount of water required to be pumped up to high levels is only a fraction of that required below. This is made use of in two ways, both of which are in use at Bowen Road, firstly in the hydraulic ram which in this case is really a horizontally mounted hydraulically operated reciprocating pump, and secondly, in water turbines which are used to drive ordinary reciprocating pumps. This latter system is also in use in the Eastern Pumping Stations. The drawback to this system lies in the difficulties of regulating the distribution requirements of the two areas to fit the respective quantities of drive water and consequent pump output.
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DISTRIBUTION.
Frequent references have already been made to the difficulties of distribution. These difficulties are fundamental to the nature of the Colony. The number of small reservoirs spread around the Colony has already been referred to, also the difficulty of concentrating filtration to one point. In addition there is the wide variation of level in the areas of supply and perhaps most important of all when it comes to the actual running of the system, the failure of new construction even to cope with growing demands. The additional complication of the rider mains has fortunately now been eliminated though this too has left a legacy of too many small mains and not enough large ones in the distribution areas.
To illustrate the distribution problems Plates 5 and 6 have been prepared. They illustrate diagrammatically the distribution systems on the Island and Mainland respectively.
On the Island alone there are nine distribution areas, the main ones of which have several feed points which involve sub-division of the areas so that in general at any given time the water in any street will be coming from one definite service reservoir. This is effected by having only a limited number of interconnecting mains which can be closed at various points so that the supply area from one reservoir can be extended or shortened at will. In the head office the engineers in charge of supply have large maps of their areas in which all mains are shown together with all control valves. Closed valves are marked with flags, so that they can see at a glance how the systems are being controlled.
The Kowloon system is much simpler as there are at present only three areas.
The difficulty in operating these control valves, or cut-line valves as they are called, arises either in the supply area or with the storage reservoirs. In the first case an increase in demand, due probably to a sudden increase in temperature, may result in some service reser- voirs being drawn down faster than others. These reservoirs cannot be allowed to get too low, therefore, when a service reservoir level is dropping too fast the Engineer has to choose between two alternatives. He may either reduce the supply area, i.e. close in his cut-lines, or increase the feed to the reservoir. This latter may not be possible, if the filters supplying it are already working at maximum output, and even if the filter output could be increased, it may not be desir- able, as that in turn might result in drawing down its storage reservoir system too low compared with other reservoirs.
The distribution, therefore, becomes a problem of so balancing the supply areas that all reservoirs are drawn down together. Before the
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