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Slurry valves, abrasion and lowering TCOs

Product News Tuesday, September 15, 2015: Weir Minerals Africa (Pty) Ltd

In response to recent tougher times in the mining and mineral resources sectors, Weir Minerals has adopted a holistic approach to its product and solutions offerings. “We are providing an increasingly complete range of products and solutions for every conceivable minerals processing application,” begins Steyn.

With the acquisitions of crushing and separation equipment OEM, Trio Engineered Products, Weir Minerals can now offer an extensive range of crushing equipment – including jaw, cone and gyratory crushers – along with screens, feeders, washers and conveyors. “On mill circuits, we are able to supply equipment for every aspect of ore processing, from milling all the way through to the tailings line: mill liners; screens; mill circuit pumps; rubber linings for pumps and pipes; cyclones, cyclone feed pumps and separation equipment; and a complete range of valves and actuators for all slurry, dewatering, separation and dosing applications,” Steyn says.

Underpinning Weir Minerals’ approach is the application of advanced wear resistant materials in their products due to the highly abrasive nature of today’s minerals processing circuits, and to seek innovative ways of simplifying maintenance tasks, such as replacing liners.

“Across our product offering, we base our decisions on lowest total cost of ownership (TCO) principles. In the current global market, lowering operational costs per ton is vital, which, along with increasing throughput levels, makes uptime a critical factor for success. We develop products to directly suit the application, wear and maintenance needs of our customers, ultimately, to offer them the lowest possible TCO solution,” he assures, citing the company’s Isogate® slurry valves as an example of this approach.

Isogate® slurry valves are manufactured in Weir Minerals’ world-class manufacturing facilities in Bangalore, India. “The range includes push through knife gate slurry valves with pressure ratings of up to 50 bar, the highest pressure rating possible for this technology. These are widely used in on/off slurry control applications for the full spectrum of minerals.

Describing the push through system, Steyn says that, when closed, rubber seats surround the knife-blade of the valve and, when open, these seats seal against each other to keep the valve leak tight.

“On actuation, the knife-blade pushes through slurry product in the valve, opening the seats. The base of the knife pushes though the bottom of the seal, expelling a little of the slurry product,” he explains.

The alternative to push through knife gate valves is the closed-bottom valve, which has a closed seat at the base of the valve where the knife rests. “With these valves, a gradual build up of solids can accumulate along the seat line, which prevents the knife from seating properly. This makes conventional closed bottom valves less suitable for slurry applications,” Steyn adds.

Referring back to the TCO of Weir Minerals’ slurry valves, he says that Isogate® push through knife gate valves come with a set of elastomer sleeves that are replaceable in the field. The design enables the valve to be quickly unbolted and opened for the sleeve to be extracted and replaced, before reconnecting the valve to the piping circuit. “A complete seal set replacement cost is 5 to 10% of the valve’s replacement cost. This makes refurbishing these valves very cost effective. In addition, maintenance downtime is significantly reduced,” he notes.

The Isogate® MP double acting mechanical pinch valve range, which closes by pinching a Linatex® premium rubber sleeve along the flow centerline, “also has field-replaceable sleeves and, in common applications such as gold, chrome and copper processing circuits, the Linatex rubber we use can last four to five times longer than competitor equivalents in certain conditions – and replacement sleeves cost 20-25% of a valve replacement,” Steyn tells MechTech.

“Many cheaper slurry valves do not provide easy access to the liner, which means that the valves either have to be switched out for refurbishment offsite, or scrapped and replaced,” he suggests, before highlighting some global success stories.

At an open pit copper mine in Arizona in the US, a client was experiencing repeated failures on their knife gate valves, which were premium-brand closed-bottom valves. “What typically happens with these valves is that abrasive debris   builds up in the seal. Eventually, the blade can’t seal properly and slurry leaks though, causing accelerated abrasion on the bottom edge. Once this has happened, the valve is irreparable and has to be replaced,” he relates.

“The competitor in this case suggested an exchange programme, at 80% of the replacement cost. But by adopting 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 superintendent, 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 recommended and installed. Following seven months of smooth operation, the Isogate® valves have more than proved themselves in the tailings line. “We wanted something 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 production,” according to Tim Shearman, maintenance 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 being fitted to replace all failing units and not one of the new valves has required any maintenance so far,” said Shearman.

“While traditional push through valves are a little more expensive, if you look at downtime and failures, they do not often offer the best TCO. We are finding that replacing closed-bottom valves almost always improve 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 conditions,” he continues.

Weir Minerals has recently added products from US-based Delta Industrial Valves Inc.to its global product portfolio. These Delta Industrial™ valves are high performance, 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, accommodating a pressure range from 20 to 100 bar,” Steyn adds.

To overcome the inherent debris problem of traditional closed-bottom designs, the Delta Industrial™ valves incorporate guided shear gates that can repeatedly close to provide bi-directional, zero leakage 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 knife gate to crush, cut, sever and expel solids that may be in the fluid stream.

“This, in my view, makes Delta Industrial valves 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 the 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.

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 recently 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.