Fluid & Gas Flow

Heavy-Duty Knife Gate Valve Resists Slurry Damage

October 8, 2014

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Credit: General Chemical Industrial Products

Flowrox, a manufacturer of pumps and valves, has commercialized a knife gate valve that is engineered for heavy-duty industrial use. The SKW slurry knife gate valve has a number of design features that are intended to better regulate - and withstand - the flow of heavy, abrasive, and corrosive media.

"The number-one application for this valve is mining," said Todd Loudin, president of Flowrox Inc., based in Linthicum, Md., the U.S. division of the company, whose headquarters is in Lapeenranta, Finland. Another application he cited is the scrubber systems of coal-fired plants, especially those used in FGD (flue gas desulfurization) scrubbers for cleaning exhaust gases.

"The slurry of water and ash that is produced in this process is so abrasive that only a specially designed valve can withstand it," he explained. "A conventional knife gate valve would not last."

In addition to these applications, Flowrox identifies several others for which the SKW valve is targeted: metal industries; mineral processing; power generation; sand, gravel, and cement operations; and water and wastewater treatment.

The company first reported plans to add the valve to its product line last spring. Commercialization of the device was announced this month.

Flowrox designed the valve with a one-piece body. Where many competitive knife gate valves bolt two body pieces together, the unitary cast iron SKW body provides extra security against leaks, according to the company.

An important feature of the design is an elastomeric load-distribution ring that is integrated into the valve sleeves. This prevents excess compression during installation and assures that a full seal occurs between the ring sleeve and the metal valve gate during operation.

"We incorporate these load-distribution rings in every valve," Loudin said. "Customers often aren't sure if they do or do not want these rings. By putting them in every valve, it eliminates a potential source of problems and gives customers a significant operational advantage."

Another important design feature is the spring action of the two rubber sleeves that are used in the valve. Loudin said these sleeves are made of either EPDM (ethylene propylene diene monomer), nitrile rubber, or natural rubber. What affects performance is the way each material is formulated and molded.

"There is a big degree of variation throughout the industry," he noted.

If the sleeves do not have insufficient spring action, they will tend to be highly loaded and more prone to damage or failure, even if they are rated at high pressure-resistance levels. "If a user adds psi resistance to the sleeves, he will need more spring action than available in some designs, and they often fail from the stress," Loudin said, adding that Flowrox designed the ring sleeves to ensure tight closure even at maximum rated pressures.

The technique of increasing the spring action of the elastomer sleeves is "fairly proprietary," he added.

The SKW slurry knife gate valve is designed to withstand abrasive slurries. Credit: Flowrox

The SKW slurry knife gate valve is designed to withstand abrasive slurries. Credit: Flowrox

There is, moreover, no way any supplier can guarantee a precise lifetime of the elastomer sleeves. "There are just too many variables such as the type of slurry, its abrasiveness, pressure, and temperature," Loudin noted.

Other features of the SKW slurry knife gate valve include component simplicity - there are only three service parts: the ring sleeves, upper seal, and valve gate. The valve achieves full isolation of medium in demanding conditions, provides free bidirectional flow and tolerates backflow, and is designed for easy maintenance.

The SKW valve also has a universal tower design that permits the installation of any actuator a user wants to use.

Major Asia-Pac Show in 2015

It's never too early to begin planning for business - and business trips - next year. For equipment manufacturers and suppliers looking to expand or enter the Asia-Pacific market, Pumps & Valves Asia 2015 in Bangkok, Thailand, is shaping up as an important exhibition and conference.

Scheduled for June 10-13 at the BITEC exposition center, the annual show is touted by organizers as the largest in Southeast Asia dedicated to pumps and valves. Exhibitors from at least 30 countries will be on hand, and six national pavilions are planned: Singapore, Japan, China, Taiwan, South Korea, and Germany. The conference side of the event will include more than 100 presentations on pump and valve developments, technologies, and applications.

Asia-Pacific is a region with bright growth prospects for pumps and valves, as countries modernize - or build new - water, wastewater, energy, and chemicals infrastructure and expand their food processing, biotech, and other industries to keep pace with population growth and consumer demand.

Information about the event can be accessed at www.pumpsandvalves-asia.com.