Mechanical Technology

⎪

Pump systems, pipes, valves and seals

⎪

Mechanical Technology — September 2015

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.

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

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

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.

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.