Selecting the correct valve for control applications normally poses many challenges to design engineers. In applications where particular fluid media is difficult to control with conventional valve designs – operational problems, maintenance and service life require thorough consideration. Helping to ensure that technologically advanced, quality products are available to meet the demands of design engineers is the Control/Energy Division of Dupleix Liquid Meters (DLM), headed up by Marc von Ruben.
DLM has been formally appointed as a valves and actuator supplier for the innovative Skorpion Mine Project. Products supplied by DLM to Skorpion Project Joint Venture include Hattersley millcentric eccentric plug valves, Habonim compact actuators and Technova butterfly and cylindrical plug valves.
Slurry applications
Hattersley Newman Hender (of Ormskirk, UK) is the only British manufacturer of cast iron eccentric plug valves and DLM is the exclusive southern African distributor of this product. The Hattersley millcentric eccentric plug valve's design offers well-suited slurry solutions. Manufactured in cast iron, ductile iron and stainless steel, using high pressure moulding techniques for consistent quality and precision, the valve also incorporates a welded nickel seat for corrosion resistance, specially profiled for low torque and extended seat life. In the case of abrasive slurries, including those found in power station ash plants, a special combination of natural rubber lining and hard, tempered ductile iron plug provides a long life and trouble-free operation.
Corrosive and abrasive applications
PCC Flow Technologies of Switzerland manufactures the Technova range of valve solutions for easy shut-off, flow control and throttling of any corrosive and abrasive liquids, gases and powders. Technova's ability to produce high quality butterfly and cylindrical plug valves in exotic materials and linings enabled DLM to secure the Skorpion Frame Agreement for on-off valves. In particular, DLM was able to meet a Skorpion requirement for valves suitable for a corrosive leaching process by supplying Technova PTFE-lined butterfly valves with titanium discs.
The Habonim Compact pneumatic quarter-turn actuator (manufactured by Habonim Industrial Valves, of Israel) has been developed to be simple, reliable and efficient. The Compact's patented rack and pinion design provides a saving in energy by giving maximum torque with minimum air consumption. The four-rack design permits air pressure to be applied simultaneously to four pistons, significantly reducing the actuator's overall size while producing higher torque when compared to single and double rack designs. The Compact's four racks also achieve more uniform load distribution than single and double rack actuators - greatly reducing wear at the points of contact between rack and pinion. The Compact actuator was fitted to both the Hattersley millcentric and the Technova butterfly valves.
Knife gate valves
DLM also identified that the southern African market was in need of a cost effective knife gate valve that would be capable of years of reliable operation in severe service applications. A worldwide search lead DLM to Vaas Industries, which develops and manufactures a wide range of knife gate valves.
Vaas knife gate valves were developed to cater to specific services where conventional valve designs proved to be inadequate. For instance, fluid media with significant solid content is generally difficult to handle with conventional valve designs such as gate, globe, ball, plug or butterfly valves. The design of the Vaas knife gate valve ensures minimum contact between moving parts of the valve. The gate is held between strong layers of gland packing and does not contact the body until it actually seats. The seating is accomplished with a non-sliding motion of the gate towards the body (seat) aided by jams located in the body. Avoiding sliding contact between gate and body permits this valve to handle abrasive particles present in the media more effectively than conventional designs. The knife gate valve is unidirectional low-pressure valve ranging in size from 50 mm to 1200 mm with pressure ratings up to 1 MPa. Modifications that offer bi-directional shut-off are also available.
Knife gate valves are normally round-port designs, however, square and rectangular port variants are also available which are typically used in hopper isolation applications. This is the only valve design that tolerates differential thermal expansion of its parts without affecting its functionality, thus making the Vaas knife valve a suitable choice for high temperature media. Another variation is the v-orifice design that offers a compromise between controllability and capability to handle media containing solids such as sludges or slurries.
Additional services
To complement its range of control valves, DLM provides ancillary equipment that includes gearboxes, positioners, limit switches and pneumatic as well as electric actuators. DLM sees itself as one of southern Africa's leading innovators in the engineering of over-pressure protection; flow, level and density measurement; automation and control solutions. The company offers a comprehensive range of products sourced from leading international manufacturers, providing optimum solutions in a wide range of industries. DLM has seven branches countrywide - in Cape Town, East London, Pinetown, Rustenburg, Welkom and Vereeniging - and its headquarters are in Longmeadow, just outside Johannesburg.
For more information contact Marc von Ruben, Dupleix Liquid Meters, 011 457 0500, [email protected], www.dlm.co.za
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