and the first deliveries into supply of treated water were made early in July.
Because of the existence of soft low lying ground adjacent to the river, the low lift, or raw water, pumping station is sited on firm ground above flood level about 1,000ft. from the river.
Beneath the floor of the pumping station is a 44ft. deep sump into which raw water is fed by four 36in. dia. siphons from a smaller sump at the intake, From the low lift sump, water is pumped to the treatment works through single 48in. dia. raw water rising main.
The whole of this system, with the exception of pumping plant and the raw water rising main, has been con- structed for stage 2 output.
Intake and siphons
The intake is a reinforced concrete structure located in the river bank. It is divided into four compartments
open on the river side, at the rear of which the siphon bellmouth inlets are located. When a siphon is in opera- tion river water is drawn into the ap- propriate compartment past a trash boom and bottom flap gate designed to exclude bed load.
Each of the four 36in, dia. siphons is equipped for control purposes with a butterfly valve at each end of the pipe. Siphonic action is usually initiated by means of vacuum pumps at the low lift pumping station. Al- ternatively, under favourable water level conditions, an operating siphon can be used to prime an adjacent siphon.
The siphons consist of concrete- lined welded steel pipes with an outer protection of glass fibre reinforced pipe asphalt. Joints are either welded spigot and socket or mechanically coupled. The intake is served by a travelling gantry crane of 3 ton capacity.
Low lift pumping station showing general progress on the pump hall
38
Assembling an inlet pipe into one of the settling tanks
The low lift pumping station houses five vertical-spindle, mixed-flow, fixed speed pumps with a total nominal capacity of 48 m.g.d., against a total external head of 88ft., together with associated starter and control equip- ment. The pumps are driven by 3,300-V wound rotor induction motors. Air break stator contactors are used in conjunction with drum controlled metal grid rotor resistors for starting. Provision has been made in the station for the installation of another three pumps for the stage 2 development.
The pumps are manually controlled but protection systems are provided to trip the pumps under abnormal operating conditions. The main pump hall is served by a 10 ton electrically operated travelling crane.
Before entering the main pump sump from the siphon delivery cham- ber, the raw water passes through self-cleansing band screens which are designed to remove suspended ma- terial larger than 5/16in. The main pump sump is divided into two parts for inspection and cleaning purposes, and one bandscreen is provided at the entry to each half of the sump.
The pumps deliver into a manifold leading to the 48in. concrete-lined welded-steel rising main.
Basic treatment
The basic treatment applied to the raw water is clarification by coagula- tion and settlement, rapid filtration, and post-filtration alkalinity adjust- ment and sterilisation.
The structures consist of 24 settling tanks, eight sand filters with filter control galleries, an administration block, and chemical building. The stage 2 development will require duplication of the settling tanks and filters, but the chemical building and administration block are already de- signed to work with the increased output.
The raw water rising main delivers river water into a mixing race at one
Far East BUILDER, August 1968.
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