A project from the National Trust of WA
A self-guided drive trail between the Perth Hills and Western Australia’s Eastern Goldfields. Go with the Flow. Follow the water to discover more about the audacious goldfields water supply scheme and Engineer CY O’Connor.
“Future generations, I am quite certain will think of us and bless us for our far seeing patriotism, and it will be said of us, as Isaiah said of old, ‘They made a way in the wilderness, and rivers in the desert”
Visitors to the No.1 Pump station may well wonder what is the purpose of the large concrete underground tank west of the pump station. The answer is that it was built as a consequence of the severe aeration problems which occurred in the early days of the pipeline operations.
In 1906 a significant increase in the pumping head, or resistance to flow, was noted at one pumping station. When the whole pipeline was tested it was found that every section of the pipeline had suffered a reduction in carrying capacity of between 12 percent and 53 per cent.
When a number of pipes were removed for examination, the reduction in carrying capacity was found to be due to extensive tuberculation in the form of round, spongy, black tubercules of up to 30 mm in diameter, predominantly consisting of iron oxides which formed pittings in the steel pipe of not more than 3 mm in depth. On the recommendation of the Engineer-in-Charge, William Reynoldson, the Government engaged a group of specialist consultants, Sir Alexander Binnie, Son and Deacon, Sir William Ramsay and Mr Otto Hehner, to advise on remedial measures.
The consultants’ 1909 report (known as the ‘Binnie Report’), concluded that internal corrosion was principally due to dissolved oxygen contained in the scheme water which could be removed by spraying the water into a vacuum. From their own experiments the consultants found dosage of the reservoir water with lime, thus lowering the acidity of the water, appeared to largely prevent corrosion. They recommended that the reservoir water should be treated by both vacuum deaeration and dosage with lime.
An inter-departmental government board of engineers and scientists, chaired by Engineer-in-Chief, James Thompson, decided to adopt the lime dosage treatment, and to supplement it later, if necessary, with vacuum deaeration. Other structures along the pipeline, such as summit tanks, were to be provided to minimise aeration of the water in transit.
The board proposed that a lime dosage pit be built next to No 1 Pump Station on its western side and that all water coming from the reservoir should be dosed with lime before being pumped to Station No.2. While the tank was being built and, in order not to delay water treatment, it was decided to commence the treatment as soon as possible using the receival tank at No 2 Pump Station as the mixing tank.
The dosing commenced in October 1910 using quick lime slaked with water so as to give about 4 grains of free lime per gallon of water. However within two years the reduction in carrying capacity of the main between pumping station No.2 and Baker’s Hill tank due to deposition of calcium carbonate in the pipeline caused by the lime treatment at Pump Station No. 2 had become so bad that over 3 kilometres of pipeline had to be removed and replaced with clean pipes.
When the large lime settlement tank on the western side of No 1 Pump Station had been completed in June 1913 the lime treatment process was recommenced at that station. Not surprisingly the carrying capacities of the pipes between pumping stations Nos 1 and 2 and also of the clean pipes downstream of No. 2 station decreased steadily over the next eighteen months due to carbonate deposition.
Nor did the test pieces, inserted in pipeline bypasses in 1910, indicate that the lime treatment had been any more successful in arresting pipe corrosion after 1913 than it had between 1910 and 1912, and in 1915 lime treatment was abandoned.
Deaeration of Mundaring water
The Binnie report of 1909 indicated the principles along which an apparatus could be designed to remove dissolved oxygen from scheme water before it left Mundaring. When it became increasingly clear that lime treatment was ineffective, the GWS engineers designed a full scale deaeration plant capable of treating 27,000 kilolitres of water per day, according to the principles suggested by the consultants. The plant was built by the State Implement and Engineering Works at Rocky Bay, North Fremantle. It was installed just east of pumping station No.1 and commenced operation in December 1917.
Valves on the 762mm pipe from the Weir to the pumping station diverted the full flow to the deaerator structure which was built 60 metres east of the pumping station. It consisted of an elevated tank, 6.7 m in diameter and 2.1 m deep containing two deaerator units, each capable of treating 13,500 kilolitres per day. Each unit consisted of two vertical steel cylinders interconnected one above the other, the upper 1.7 m in diameter and the lower 1.1m. Both cylinders were evacuated by vacuum pump through a 127mm diameter pipe in the top of the upper cylinder. This pipe also removed the extracted gases.
Water was forced into the bottom of the upper cylinder by atmospheric pressure through in excess of a thousand 3 mm diameter holes, shooting as a fine spray to the top of the cylinder, impinging on a plate and falling back to enter the lower cylinder through a second plate containing similar 3 mm diameter holes. The spray fell through the lower vacuum cylinder and exited into a pipe returning to the 762mm diameter main which ran under the pumping station to the stand pipe surge tower on the west side of the station from which it was distributed to the pumps.
Untreated water from Mundaring reservoir contained an average of 8 parts per million (by weight) of dissolved oxygen in summer, and 10 parts per million in winter. After the water had passed through the deaerator its oxygen content was found to be between 0.7 and 1.0 parts per million, indicating that about 90 percent of the dissolved oxygen had been extracted.
The deaerator was an essential element in the prevention of further internal corrosion, although it did little to prevent corrosion at the lead joints between pipes where a more radical solution was required. The success of deaeration, however, depended on how effectively air could be prevented from entering the pipeline along its full length. This was not an easy task because of the wide variety of potential entry points and the work took over ten years to be fully completed.
To reduce air entry at the pumping station receival tanks and at the regulating tanks on the pipeline the inlets to the tanks were repositioned to discharge under water near the bottoms of the tanks. Under the original pumping system the high points of the pipeline between pumping stations were only full when the pumps were operating. To reduce daeration the Binnie report recommended that the main be also kept full of water during periods when the pumps were not working. To achieve this six summit tanks were
installed in 1910 and 1911 at the high points between stations. These were at Sawyers Valley between pumping station No. 2 and Baker’s Hill tank; at Kellerberrin West between stations 3 and 4; at Booraan between stations 4 and 5; at Nulla Nulla between stations 5 and 6; at Bronti between stations 6 and 7; and at Koorarawalyee (pronounced Coo-rarra-wally) between stations 7 and 8. The installation of these tanks made a significant change to the way the whole scheme was operated.
Under the original scheme the length of pumped main was 406 km and the length of gravity main was 155 km. The gravity main was in two sections, from Baker’s Hill to Cunderdin and from Bullabulling to Kalgoorlie. With the summit tanks in place the pipeline became predominantly a gravity main with the pumped length reduced to 123 km and the gravity length increased to 438 km. This was because for each section between pumping stations the first station only had to pump to the next summit tank. The water then gravitated to the second pumping station.
A lot of the credit for the successful re-vamping of the scheme should be given to the then Principal Assistant Engineer Walter (Kirk) Weller, the last of C Y O’Connor’s cadets still in the Department. He was responsible for converting the laboratory scale deaeration plant proposed in the Binnie report into an innovative fullscale plant capable of deaeration of 27,000 kilolitres of water per day which, in association with the alterations made at tanks and reservoirs, largely solved the problem of pipeline internal corrosion except that occurring at the lead joints between pipes. The deaeration plant remained in operation until the Second World War.
Prepared by Don Young based on research by Dr Richard Hartley
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