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Powder & Bulk Solids, June 2018

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TechnicalExclusive 20 J u n e 2 0 1 8 A NFPA Guidelines: Replacing Your Uncompliant Parts Ashes to ashes, dust to dust. When your valves are compliant, they'll never combust. Alright, so we might not win any poetry awards — but when it comes to valve compliance, we're at the top of our game. Here's what you need to know to ensure your rotary valves are compliant with NFPA safety regulations. Anatomy of a Rotor When you're checking for NFPA compliance, you'll first want to make sure your valve has metal tips on the rotor assembly, as well as the outboard bearings. Mild steel, stainless steel, and AR400 steel will all work depending on your applica- tion, as long as the material is not rubber-tipped. Rubber or plastic tips will not withstand the pres- sure of a deflagration. Beyond that, you can have either an open-end or closed-end rotor. Rotors should have a minimum of eight vanes. Six-vane rotors are uncompliant, but if your rotors have eight, ten or twelve vanes, they'll generally be compliant. Staying in the Clear Rotor clearances are one of the biggest indicators of NFPA compliance. To quench the spread of flames along your conveying line in the event of an explosion, your rotor-to-housing tolerances must stay under the maximum of 0.0079 in. You can do this in one of two ways: Either by mea- suring directly through the opening of your valve's inlet or outlet, if it's accessible, or by re- moving the endplate to take your measure- ments. You can find a more in-depth guide to the process at www.acsvalves.com/blog. In other words, your maintenance program should involve regularly checking these clearances to make sure your valves stay compliant. If the tolerance ever goes above 0.0079 in., it's time to replace your rotor assembly. Explosion Prevention The maintenance and replacement stan- dards don't vary too much across different applications. That said, if you're working with more abrasive materials, we recom- mend going with a more abrasion-resistant rotor assembly to prevent wear and in- crease the lifespan of your valves. Your rotary valves will generally be paired with an explosion prevention sys- tem, which you should also check periodi- cally to make sure everything works as it should. The dust collector should have an explosion release vent and a passive isolation flap valve to complete the flame- quenching system. Many dust collectors will have an FT-style valve, which is a fabricated valve with wiper blades on the rotor tips. There are valves available for airlock appli- cations that act as a drop-in replacement for some of those FT valves. If any of your existing valves with the flex tip need replacing, a drop-in replacement can help you comply with NFPA rules. Further Reading Looking for more information on NFPA compliance? Feel free to read this breakdown of NFPA 652 or this overview of plant deflagration — or, if you feel confi- dent in your intel, take our NFPA Quiz at www.acsvalves.com/blog to test your knowledge. By Brittany Dollimore, ACS Valves NFPA tolerance check

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