In pneumatic conveying systems, a significant challenge often revolves around the wear life of rotary valves. Rotary airlock valves remain a staple in the industry, excelling at both material metering and creating a seal under differential pressure. Although not flawless in either function, they are a versatile solution, akin to the greatest invention since sliced bread, as they accomplish both tasks simultaneously.

However, their performance is not without a drawback. It relies on maintaining tight clearances that can erode over time. Frequently, we receive calls from customers inquiring about how to assess wear and whether they can check the tolerances.

CAN YOU ASSESS TOLERANCES ON YOUR ROTARY VALVE?

Technically, using feeler gauges allows for tolerance checks, but it's crucial not to make replacement decisions solely based on this method. Rotary valves exhibit uneven wear patterns; some wear on one side more than the other (refer to the image above). The extent of wear depends on the handled material and application conditions. Blow-by-air, a common cause of wear, indicates that the rotary valve is not meeting its designed feed rate and may require replacement soon.

WHAT CAN BE DONE TO ADDRESS ROTARY VALVE WEAR?

Manufacturers employ various strategies to enhance rotary valve resistance to abrasion. At BlowVac Systems, we offer configurations with Nedox® chrome, Hard Chrome, or ceramic on the bore and end plates, along with hardened steel or tungsten carbide-coated tips. These features can significantly extend the rotary valve's lifespan in diverse applications compared to more basic alternatives. Additionally, Cavity Air Purge and Shaft Air Purge serve as protective measures against wear.

However, a frequently overlooked aspect by both customers and manufacturers is the design of the conveying system itself that the valves serve. The primary variable affecting wear is the differential pressure from above to below the valve. In pursuit of cost savings, manufacturers often design lines to operate at higher pressures in smaller lines that could function effectively at lower pressures in larger lines. A useful analogy is having 3 lanes versus 4 lanes during rush hour traffic. Although this upfront approach saves capital, it can lead to increased costs and downtime due to more frequent rotary valve replacements in the long run.