Far too much maintenance is being done at South African mines, which, in turn, has a negative effect on productivity in an already volatile sector, polyurethane moulding company Urethane Moulded Products (UMP) MD Trevor Carolin tells Engineering News.

He points out that UMP and valve manu-facturer Dual Products International have jointly invested in developing new valves, lined with polyurethane sleeves, which were officially launched in South Africa in April.

“This range of Dual slurry knife-gate valves, wafer slurry knife-gate valves and Dual urethane-lined slurry knife-gate valves is a breakthrough in valve technology and is exclusively available through Dual Products International’s range of Dual valves, making it the only company in the world to supply urethane sleeves for a Dual slurry knife-gate valve,” Carolin asserts.

Moreover, he says these valves have been tested under pressures of up to 40 bar on slurries in different mining applications, including gold and uranium, with positive results.

Carolin adds that the initial tests, during which the effectiveness and durability of the polyurethane sleeves were tested against those of rubber sleeves using water, were undertaken in 2012, in Finland.

The results showed that the knife-gate valve, with a polyurethane sleeve, could handle 75 000 strokes, compared with only 5 000 on a rubber sleeve.

“These results were some of the main reasons why polyurethane was selected for the valves,” he explains.

Carolin says the Dual slurry knife-gate valve is manufactured with a spheroidal graphite iron casting grade 42, or fabricated body, and features a heavy-duty stainless steel blade. The removable sleeves on either side of the blade provide a bidirectional bubble-tight seal, ensuring that no metal parts come in contact with the slurry.

He states that the wafer slurry knife-gate valve is manufactured with a steel body and features a heavy-duty stainless steel blade. Removable sleeves on either side of the blade provide a bidirectional bubble-tight seal, which prevents any metal parts coming into contact with the slurry.

Carolin notes that, when the knife gate is open, it is fully withdrawn from the slurry flow.

The Dual polyurethane-lined slurry knife-gate valve is manufactured with a cast iron body and features a heavy-duty stainless steel blade.

“The one-piece polyurethane liner is moulded throughout the body and chest area of the valve. A cutaway in the polyurethane liner on the downstream side assists in cleaning out the seating area and the valve also features a high-chrome/urethane deflec-tor cone, which protects the urethane seat from the main stream of the slurry flow,” he points out.

Hence, Carolin highlights that process plants are being designed for higher through-put and that the life expectancy of modern mining plants have ultimately been shortened, owing to increased operational levels.

“Equipment is being designed for a specific life expectancy and no more. For this reason, engineers are moving away from traditional rubber lining and towards more cost-effective lining alternatives.”