Mechanical Technology September 2015

⎪ Pump systems, pipes, valves and seals ⎪

Left: Weir Minerals Africa’s integrated offer- ing pairs Isogate ® valves with Linatex ® hoses and rubber lining and Cavex ® hydrocyclone clusters. Centre: Isogate knife gate valves installed at Mount Thorley Warkworth. Below: Production of a three-way Cavex clus- ter incorporating Linatex premium rubber and Isogate knife gate valves. Locally, Steyn cites Trident’s Sentinel copper project as an example of the success of Weir Mineral’s holistic and TCO focused approach. “On the valve side alone, Weir Minerals supplied 611 Isogate knife gate slurry valves in various sizes and actuator types. Sentinel re‑ cently ordered a substantial number of additional valves, which is testament to being satisfied with our high quality, high performance and cost effective valve offering,” he concludes. q knife gate to crush, cut, sever and expel solids that may be in the fluid stream. “This, in my view, makes the Delta Industrial valve one of the best closed- bottom isolation valves for applications where traditional equivalents fail due to debris accumulation along the bottom seal,” Steyn explains. The full port design of Delta Industrial valves also helps protect the sealing surfaces from erosive and abrasive flows while allowing maximum volumes at minimum pressure losses. “We also own the BDK brand of valves: a complete industrial range of gate, globe, check, ball, plug, diaphragm and butterfly valves. And in the Isogate range, disc-type non-return valves and autoball double non-return valves for quick changeover between a duty pump and standby are also available – and these use Linatex premium rubber,” he adds.

being fitted to replace all failing units and not one of the new valves has required any maintenance so far,” said Shearman. “While traditional closed-bottom valves are a little less expensive, if you look at downtime and failures, they do not often offer the best TCO. We are find‑ ing that replacing closed-bottom valves with push-throught valves almost always improves reliability and uptime,” Steyn informs MechTech . But closed-bottom knife gate slurry valves have an important role to play in some applications. “If slurries are very corrosive, for example, or very valuable, then leakage has to be prevented. Closed- bottom valves can also handle higher pressures and temperatures, because they are available in a host of different materials to suit specific slurry condi‑ tions,” he continues. Weir Minerals has recently added products from US-based Delta Industrial Valves to its global product portfolio. Delta Industrial™ valves are high perfor‑ mance, zero leakage and closed-bottom knife gate slurry valves. “The Delta Industrial range consists of valves made to ASME B16.34 in classes 150 and 300 (PN20 and PN50), along with some Class 600 (PN100) products, accom‑ modating a pressure range from 20 to 100 bar,” Steyn adds. To overcome the inherent debris problem of traditional closed-bottom de‑ signs, Delta Industrial valves incorporate guided shear gates that can repeatedly close to provide bi-directional, zero leak‑ age isolation, no matter what the pipe contains. The gate’s chisel-shaped tip is fully guided in its travel and brings a shearing action to a machined interface in the valve body. Guiding concentrates the tip’s force at a point, allowing the

gested an exchange programme, at 80% of the replacement cost. But by adopt‑ ing our push through Isogate WS knife gate slurry valve, the root problem was solved. A flushing plate was added to the bottom of the system to overcome their leakage concerns. Compared to the 80% exchange cost, we are able to reduce this to a liner set replacement cost of between 5% and 10% of the valve cost and we achieved an eight-fold life improvement between replacements,” Steyn tells MechTech . At a semi-soft coal tailings operation at Mount Thorley Warkworth in New South Wales, Australia, mine superin‑ tendent, Gary Cooke described a valve problem: “After a short time with the valves not operating, the tailings would dry out and thus restrict the blade from moving through its operation.” A Weir Minerals push through Isogate valve for slurry applications was recom‑ mended and installed. Following seven months of smooth operation, the Isogate valves have more than proved themselves in the tailings line. “We wanted some‑ thing that would be easy to operate, easy to maintain and have very good reliability, and that’s what we have with these valves,” said Cooke. “These are huge pluses for productivity.” At Oceana Gold’s Macraes processing plant in New Zealand, failure to seal was preventing routine maintenance on the downstream pumps. “This was causing costly downtime of the Pressure Oxidation plant, essentially ceasing gold produc‑ tion,” according to Tim Shearman, main‑ tenance planner for the plant. The cause was again traced to the closed-bottom valves being used and, by changing over to Isogate push through valves, maximum uptime was restored. “Isogate valves are

Mechanical Technology — September 2015

11