PBS_Powder & Bulk Solids

Powder & Bulk Solids, June 2018

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Powder & Bulk Solids TechnicalExclusive 28 J u n e 2 0 1 8 Flexible tips are generally used only in gravity flow applications, but can be used in lower pressure differential situations like a dust collection system. In higher pres- sure differentials, the flex tip will pull away from the housing and cause excessive leakage. Flexible tips may be produced out of almost any rubber. They are often utilized on larger particle size or fibrous products that would typically jam a solid vane rotor. If a particle becomes trapped between the flex- ible tip and the housing, the tip either gives way allowing it to fall into the next pocket or drags it around to the outlet where it falls out. The rubber used for the flex- ible tip should be selected based on the maximum temperature and the type of material passing through the valve. Rotor Vane Options The most common vane treat- ment is beveled edges. Some products tend to smear or build up on the internals of the hous- ing. This smearing will cause additional drag, squealing, and may even lead to valve seizure. By beveling (or relieving) the trailing edge of the vane, this relieves the drag by reducing the surface area of the rotor. The beveled vanes also allow products to more easily escape if wedged between the rotor and housing. For open rotors, the beveling should be on the radial edge and both sides of the vanes. In applications with excessive smearing, specially designed scraper blades or cutter vanes are used to remove product buildup. Rotor Pocket Options The standard rotor pocket has a 'V' shape. While this works well is most applications, it may be- come troublesome with sticky products. A scalloped pocket ro- tor is where the bottom of the rotor pocket is rounded out to a 'U' shape and ground smooth or even polished. This is desirable in both sanitary and sticky ap- plications, allowing the material to more easily discharge from the pocket. Reduced volume is used to lower the capacity of the rotor. Smaller rotary airlocks may cause the material to bridge above the inlet. The reduced volume ro- tor allows a larger valve to be used to eliminate bridging and lower the discharge rate when you do not want to over feed the equipment downstream. Reduced volume is also used when to ac- curately feed material at a more consistent rate. Material tends to discharge from a rotary valve in clumps equivalent to the number of pockets. The reduced volume rotor allows a more even flow, consistent flow. Staggered rotor pockets include a disc through the center of the rotor and opposing pockets on each side of the disc are off center. This in effect takes an 8-pocket rotor and turns it into a 16-pocket rotor. This helps give more consistent flow for more accurate discharge. Rotor Coatings & Finishes Coatings are used to help prevent wear and corrosion, or to achieve better product release. Coatings are normally applied to fixed blade rotors only. Nickel has some increase wear resistance, but is primarily used as a less expensive alternative to stainless steel to help prevent corrosion. Teflon is used on sticky materials that tend to build up in the pockets. Stellite is a highly abrasion-resistant mate- rial that is welded onto the outer edges of the rotor, then machined down to required tolerances. Rotors may also be chrome plated for abrasion resistance. There are also various plasma coatings which offer both abrasion resistance and low coefficient of friction for bet- ter product release. Stainless steel rotors can be polished to practi- cally any finish. Application specialists at the valve manufacturer will help you specify the correct rotary airlock for your system. Information vital to selecting the best valve includes: material being handled, bulk density, particle size, ma- terial characteristics, moisture content, temperature range, equipment above and below the valve, pressure or vacuum levels, and the desired discharge rate. They should have a vast expe- rience in handling all types of products in various types of sys- tems. Selecting the correct rotary airlock valve, rotor, and design features is critical to ensure suc- cessful operation with minimal air leakage and down time, along with maximum valve life. Paul Golden is manager, Carolina Conveying, which specializes in pow- der handling components and mate- rial handling systems. The company manufactures a comprehensive range of products, including rotary airlock valves, diverter valves, gate valves, silo dischargers, screw feeders, bulk bag handling systems and portable bulk containers. For more informa- tion call 828-235-1005, or visit carolinaconveying.com Closed end rotor Drop thru rotary airlock valve www. .com Check out our Valves, Gates, & Airlocks Equipment Zone for the latest articles, equipment, and news PowderBulkSolids.com

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