Ask Joe! Archived Article, Abrasion, Efficiency and Rotary Valves, Guest Article by Mike Griffiths, Omegaslate, Ltd.

Abrasion, Efficiency and Rotary Valves
Guest article by Mike Giffiths of Omegaslate, Ltd.

Mike Griffiths of Omegaslate is our guest columnist for this article. He discusses a common problem when handling bulk solids through rotary valves, namely wear. Our thanks to Mike for his contribution.

When rotary valves, or blowing seals, begin to wear they leak causing a reduction in line pressure and the overall output of pneumatic conveying systems, to the point where it becomes necessary to change the valve in order to avoid blockages. If there are multiple valves feeding the conveying system, wear can become a serious and expensive problem very quickly.

Traditional methods of protecting the internals of a rotary valve, such as a thin tungsten carbide coating, can improve the operating life of the valve by around 3 times, when used as protection against hard and sharp bulk minerals. Alumina ceramic can improve the operational life of a rotary valve by more than 20 times that of thin tungsten carbide coatings, before regrinding of the ceramic lining is necessary. Reaction bonded silicon carbide ceramics (RBSiC) can provide further increases in wear resistance of up to 200 times that of cast iron. (Figure 1.) shows a wear comparison of the various wear resistant products available.

Rotary valves (Figure 2.) working in positive or negative pressure environments suffer wear from air, laden with sharp abrasive particles, leaking at high velocity past the rotary vane sealing blades and also through the rotor shaft stuffing box seals.

Figure 2. Rotary Valve

Most of the wear occurs on the non-product side of the valve rotor bore. The weight of the free flowing powder being carried through the product side of the valve tends to seal the air pressure by blocking the gaps between the vane sealing blades and the rotor bore.

As the powder falls in to the air flow of pneumatic conveying system, and the now empty pockets rotate through the non product side of the valve, air and grits pass between the vane sealing blades and the rotor bore, usually at high velocity, wearing both the sealing blades and the rotor bore. The greater the pressure and volume of air and grits passing the vane sealing blades and through the rotor shaft stuffing box seals, the greater will be the wear in the valve and the shorter will be the operational life of the valve.

Diamond ground ceramic valve lining technology has been thoroughly tested and continuously refined over the past 13 years as a retrofit system, requiring modifications to be made to the valve rotor and the valve body to facilitate the lining components. These advanced systems are used to protect valves against wear and corrosion caused through handling all manner of abrasive minerals and metals, such as silica sand, ferrous oxides, pearlite, sinter, china clay, grain, mill scale, slate dust, petro-coke, coal, fly ash, fertilizer, cast iron swarf, granite dust and chippings and many other abrasive materials.

Precision advanced ceramics have proved to be the most cost effective materials available capable of dramatically reducing extreme wear in valves that are used to control the flow of bulk minerals and they can be fitted to worn and new valves.

About us: Omegaslate was incorporated in 1983 and has been involved with the design, formulation, development and manufacture of wear and corrosion resistant technical ceramics. Over the years Omegaslate's activities have centered around the design, development and manufacture of advanced ceramics based extreme abrasion and corrosion resistant systems and products for application within the bulk minerals and metals handling and processing industries.

Visit their web site at http://www.omegaslate.com or email Mike Griffiths at info@omegaslate.com for more details of their technologies and the range of products and services that offered.

Help others by posting your comments, suggestions and experiences with bulk solids feeding or any other materials handling concerns you may have on our On-Line Help Forum. For past Ask Joe ! Articles, visit the Ask Joe! Archived Articles.

Guest articles for the Ask Joe! Column are always welcome, for more information please contact Joe Marinelli directly at his email address: joe@solidshandlingtech.com.