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A giant pipeline through an Australian city has the vital job of transferring drinking water to more than a million residents. When selecting control valves for the project, engineers had to ensure that they could deal with its challenging aspects, including a wide range of flow rates, high and low pressure drop and a risk of cavitation, as Mark Gimson, marketing manager at Singer Valves,and Celso Iglesias, sales manager at PerryCo, explain.
The A$403 million North South Interconnection System Project (NSISP) is one of South Australian Water Corporation’s (SA Water) biggest infrastructure projects. It has been undertaken in the metropolitan district of Adelaide to connect the north and south drinking water distribution systems and to increase access to a desalination plant. The project included the construction of 32 km of pipeline through metropolitan main roads and suburban inner streets. Getting it done right meant fitting together a lot of different moving pieces.
To deliver this project, SA Water assembled an integrated project team comprising staff from a range of private sector companies in order to secure the right expertise and skills necessary for the success of the project. A managing contractor framework was established to deliver the ancillaries programme across the entire water network. Infrastructure engineers John Holland Group partnered with civil engineering company Leed Engineering to design, construct and commission new valve stations and upgrades to the existing network.
According to Robert Bonner, commissioning & handover manager for John Holland: “We knew our biggest challenge was going to be to complete this quickly and efficiently to allow the continuing success of the wider NSISP team to hit their milestone dates.”
Extreme conditions
Amongst a number of vendors called upon to propose technical solutions to the many phases of the project was industrial valve specialists Perryco and Singer Valve. There were several challenging applications where control valves were needed to perform in extreme conditions. There was a long consultation process to define the conditions and come up with solutions to deal with each hurdle. In addition, quality, cost, serviceability and accessibility to equipment added a whole other layer to the requirements.
They found that there were three major issues pertaining to the valves required at the ten water stations. Perryco and Singer Valve joined forces to address each of these with different technology options.
Firstly, the valves need to work primarily in high pressure drop conditions and occasionally at very low pressure drop conditions.The problem with these conditions is that they can quickly lead to cavitation. Cavitation can be an extremely damaging force causing loud noise, excessive vibration, choked flow, destruction and erosion of control valves and their components which results in disruption of water distribution or plant shutdown. To deal with this problem, all the valves were fitted with Singer’s anti-cavitation technology that contains two heavy stainless steel sliding cages that maximize the full flow capacity.
Cavitation recovery
The first cage directs and contains the cavitation recovery, allowing it to dissipate harmlessly. The second cage allows further control to a level as low as atmospheric pressure downstream. The cages are engineered to meet the flow/pressure differential of each individual application. The majority of valve stations were fitted with the anti-cavitation solution.
Secondly, over the course of the distribution system there would be a wide range of flow rates, from almost zero to maximum flow capacity. This isn’t uncommon in a distribution system, especially of this scale, but when a valve is operating in the low flow range (less than 20% open) the valve can hunt and chatter. This causes noise, pulsing pressure waves downstream and the constant open/ close movement close to the seat can lead to premature wear. Traditionally, a smaller by-pass valve is needed to control the lower flow which adds cost and more time to maintain equipment. To overcome this challenge, each valve was equipped with Singer’s single rolling diaphragm (SRD) technology. The SRD-molded diaphragm provides a constant surface area in all valve positions and avoids injecting small pressure pulses into the piping. By doing this, the valve eliminates seat chatter at low flows, helping to prevent water loss and leakage while providing smooth, precisely controlled flow.
Failure risk
With a city of 1.2 million people relying on this water distribution system, valve failure is simply not an option. Valve failure can occur in a number of ways. The most common is due to lack of maintenance on the pilot system strainer, which eventually results in plugging and with the valve unable to close.
In other cases, pilot failure can happen when, for some reason, the primary pilot system fails or plugs. This could be due to something quite simple but can bring a halt to normal operations. Finally, there can be main diaphragm failure, which is extremely rare, but it can happen due to foreign objects travelling down the pipeline. By taking all these possibilities into account, the solution was to have the Northern PR Station’s PGM 2 x 24 in main valve body installed with two independent diaphragms allowing for full back up in the event that the primary system fails. This means the valve will continue to operate normally utilizing a secondary pilot system, whilst also giving an alarm signal allowing operations to schedule maintenance.
Proven solution
The end result was a valve that addressed every concern and challenging circumstance with a real proven solution. “When you have the ability to add different technology options or accessories, it enables you to create a complete valve solution with less equipment, for a variety of extreme conditions,” said David Perry, director of Perryco. “Singer has the most comprehensive options.”
To ensure the milestones were hit on time, Perryco provided local support to resolve any issues, which included on site hands-on training sessions for the operators. By the time the project was completed, 23 valves with sizes ranging from 600 mm down to 100 mm were installed at the ten different stations. “All valves have been operating successfully, enabling SA Water to successfully transfer bulk water from the southern reservoirs and the desalination plant to the northern suburbs, securing water supplies to enable growth through to 2050,” said SA Water’s project director, Mark Dedman.
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