Material handling applications are not created equal. Seems obvious, right? But, too often, light-duty equipment is selected for extreme-duty applications. This mismatch leads to unnecessary costs, plant downtime, and frustration. Precision’s brand identity is “Solutions for Extreme-Duty Applications,” so we’ve thought a lot about what extreme-duty really means.

In this post, we’ll use rotary valves to illustrate how we think about extreme-duty. The framework presented here can also be applied to screw conveyors, belt conveyors, rotary feeders, or other bulk material handling equipment.

Defining Extreme-Duty

Objectively, some material handling applications are more difficult than others, but there isn’t a good, clear standard for differentiating extreme-duty applications. In many industries, extreme-duty relates to the abrasiveness of the material. Pet coke, cement kiln dust, activated carbon, and diatomaceous earth, are examples of highly abrasive materials.

High-temperature material is often associated with challenging applications,  particularly when the material is 500° to 1200° F. Prolonged heat can cause increased metal fatigue. High temperatures also stress “soft” components such as seals, grease, belts, and others.

Handling corrosive material is another tough challenge. Rotary valve applications handling sticky, high-moisture materials, including lignite coal, are often regarded as some of the most challenging applications.

Extreme-duty is not only defined by the parameters listed above. In our view, the distinguishing characteristic of extreme-duty is the combination of a challenging material and an extended operating cycle between opportunities for maintenance or repair.

  • Is the rotary valve being asked to run 24/7 for months at a time without opportunities for repairs?
  • Does the production schedule provide for regular down days or shifts when maintenance can be completed?
  • Does unplanned downtime come at a considerable cost? In other words, is the application one where the valve has to run?

The intersection between the difficulty of the application and the availability (or unavailability) of the equipment for maintenance provides a useful framework to differentiate easy applications, hard applications, and what are truly extreme-duty applications.

Light-Duty Material Handling

Mildly or non-abrasive materials, ambient temperatures, neutral pH, or similar attributes are typically light-duty applications. When a low difficulty application is combined with regular service availability or maintenance, the application is light-duty.

Typical applications include:

  • Rotary valves for most agricultural processing
  • Dust collector rotary valves handling wood dust
  • Some pigment and catalyst dosing applications

In light-duty applications, most rotary valves should operate for years with minimal repair cost and little unplanned maintenance. These are applications that are well-suited to low-cost equipment that can be described as commodity grade. Upgraded equipment works fine in these light-duty applications and might provide decades of useful life, but the ROI on this choice would be dubious.

Medium-Duty Material Handling

These applications share a low degree of difficulty with light-duty applications but have longer cycles between availability for maintenance.

Equipment that might be appropriate for a light-duty situation could be overly taxed in these medium-duty applications. This results in a description like “we are always repairing it… it doesn’t fail but it requires a lot of attention to baby it along.”

Typical applications include:

  • Dust collector rotary valves in some mineral processing operations
  • Rotary valves for injecting mildly or non-abrasive powders into a low pressure, less than 5 psi, pneumatic conveying line

For medium-duty applications, rotary valve upgrades are chosen to increase durability and can include wear-resistant internal coatings, heavier bearings, or the like.  The objective of these upgrades is to do enough to keep the equipment operating over a three- to six-month period. While more costly than commodity grade equipment for light-duty applications, standard grade equipment for medium-duty applications is still relatively inexpensive.

Heavy-Duty Material Handling

These applications are demanding, but the operating parameters are such that the rotary valve is periodically available for preventive maintenance, repairs, or replacement – perhaps as frequently as weekly or monthly.

Rotary valves suitable for light-duty or medium-duty applications will usually struggle mightily in heavy-duty applications. Even though the maintenance availability can be high, the valves are not designed to withstand these punishing applications. If rotary valves are being replaced every 1-3 months, it is a sure sign that commodity or standard grade valves are being used in an application that requires durable grade valves.

Typical applications include:

  • Rotary valves injecting an abrasive material into a low-pressure pneumatic conveying line
  • Dryer infeed valves in mineral processing
  • Rotary valves feeding lime to a DSI system
  • Dust collector rotary valves in metals processing

Rotary valves should be selected that can handle highly difficult materials – highly abrasive, high temperatures or other parameters. For example, valves built with abrasion-resistant metal for the rotors or with carbide or tungsten overlays on the wear surfaces are appropriate for heavy-duty applications.

The distinguishing characteristic of extreme-duty is the combination of a difficult material and an extended operating cycle between opportunities for maintenance or repair.

Extreme-Duty Material Handling

These applications really test what a rotary valve is made of – its design, the materials of construction, and the quality of the components. A long cycle between maintenance or repair availability is the characteristic that separates extreme-duty from heavy-duty.

The durable grade rotary valves that work acceptably in heavy-duty applications will usually start well in extreme-duty applications. But the severe challenges will lead to a failure well short of the desired operating cycle. “We almost made it to our annual outage with that valve…” describes this situation. Extreme-duty application challenges are solved with a superior grade rotary valve.

Typical applications include:

  • Pneumatic conveying of pet coke or diatomaceous earth
  • Slag handling
  • Discharging from a blend silo in cement manufacturing
  • Feeding activated carbon to a furnace
  • High-temperature sludge handling

Extreme-Duty Rotary Valves

Selecting valves built for extreme-duty applications deliver the best ROI. Precision’s PMV Modular Rotary Valve and PMDS Self-Cleaning Rotary Valve product families are designed and built for extreme-duty applications – the more challenging, the better.

The unique modular design and the Tri-Braze™ abrasion-resistant steel used in the construction are carefully selected to provide outstanding performance over long operating cycles.

We encourage you to reach out to us if you have an extreme-duty rotary valve application. You can contact us to discuss your most challenging rotary valve applications.


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