Slimming Down

Steve Hill & Mark Gimson

Yarra Valley Water (YVW) is the largest of Melbourne’s three water corporations, providing water supply and sewerage services to more than 1.7 million people and more than 50,000 businesses in the northern and eastern suburbs of Melbourne. The district covers approximately 4,000 sq km, from as far north as Wallan and extending to Warburton in the east. It maintains more than 9,000 km of water mains and nearly 9,000 km of sewer mains. 

The corporation’s Wandin North site had three Singer pressure-reducing valves (PRVs) of various sizes. The 50-mm (2-in.) valve was used during periods of low demand in the zone, whilst the 100-mm (4-in.) valve supplied water during periods of high demand, which left the 150-mm (6-in.) valve to supply water for extremely high-demand situations, such as firefighting. In early 2012, YVW’s field service technicians (Lend Lease) observed severe erosion within the 50-mm valve during routine maintenance at the site, so they contacted Metaval to investigate.  

Noise pollution

After arriving at the site, Metaval Sales Engineer Steven Hill noted that the noise from the valves could clearly be heard from the inground concrete valve chamber with the concrete lid on. The three valves at the site were not fitted with anti-cavitation (anti-cav) trim at the time of installation, as the design did not require it. Typically an anti-cav trim is needed when the inlet pressure is three times higher than the required outlet pressure or when the Sigma is below 0.8. Inspection showed the site’s upstream (inlet) pressure transmitters to be 68 m and its downstream (outlet) pressure transmitters to be 6.6 m; this means the downstream pressure (desired setpoint) that feeds into residential homes was fluctuating due to the cavitating valves that were struggling to provide a stable downstream pressure. Excessive noise and damage to the valve and downstream pipeline were consequences of the cavitating valve’s erosion, so it was clear that an anti-cav trim was needed and the damaged 50-mm valve would need to be replaced. 

If the 50-mm valve was replaced with an added anti-cav trim, it would still leave the other two valves vulnerable to cavitation. Smaller-diameter valves can maintain control at lower flow rates, but at the same time they offer limited capacity for high flow rates, hence the additional valves in the system. As luck would have it, Singer Valve had just added new sizes for their single rolling diaphragm (SRD), starting at 150 mm. This unique technology offers a huge advantage over a flat diaphragm-operated valve in that it does not need to be operated at between 20–80% open, so a larger-diameter valve can be used to control low and high flows in the same valve.

Most distribution systems include a combination of extremely low-flow and high-pressure periods. Traditional automatic control valves often experience seat chatter under these conditions. As a result, a smaller bypass valve is needed to control lower flows. With Singer SRD technology, the moulded diaphragm provides a constant surface area, no matter the valve position, and avoids injecting small pressure pulses into the piping. By doing this, the valve eliminates seat chatter at low flows, which helps to prevent water loss and leakage while providing smooth, precisely controlled flow. 

“It goes against the ‘rule of thumb’ to remove a smaller-diameter valve from a system and expect a larger-diameter valve to control pressure during low and high flows,” said Steven Hill. “But the SRD worked like a charm.”

So by replacing the 50-mm valve with a 150-mm SRD fitted with anti-cav trim, the need to protect the other two valves with anti-cav trim was removed, as the SRD can now do it all.

Crushing cavitation

Cavitation can be an extremely damaging force, with 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. Singer’s anti-cavitation technology features two heavy stainless steel sliding cages that maximize the full flow capacity. 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 application. 

By installing a valve with both of these features (SRD and anti-cav trim), the facility addressed cavitation and provides more stability by having one valve in control. “Another advantage that is significant over time is that we now have fewer assets requiring less maintenance,” said Yarra Valley Water Specialist Technician of Operations Fiore DiPietro. With an organization that requires 650 people to maintain operations, finding ways to reduce maintenance time and costs can make a big difference.

Yarra Valley customers are back to enjoying constant stable water pressure without cavitation noise, and YVW has extended the lifetime of its pipeline with anti-cav protection.