More Questions and Answers
Q: What are the differences between A-style diverter and K-style diverter valves, and how can we use these in our pneumatic conveying process?
A: Logan Cameron, Vortex, says:
In gravity-flow applications, certain materials achieve optimal flowrates if they're processed through a diverter with steeper, more dramatic outlet leg angles. Steeper angles are used to promote flow when handling heavier, denser materials such as aggregates. Steep angles reduce the likelihood of inline material buildup or material plugs, which can otherwise create maintenance issues.
If a diverter valve has more subtle angles, material velocity will slow, causing materials to drag along the bottom of the valve as they flow. With steeper outlet angles, material is able to suspend and flow more freely through the channel. As a result, the valve makes little contact with materials and is subjected to less wear and abrasion, which furthers the valve's useful life.
A common misconception about a diverter valve is that its blade can be shifted "on the fly" to divert material toward different locations as material flows through it. While the equipment does have the mechanical capabilities to do this, actuating a diverter in a continuous material stream is harmful to the diverter's functionality. As the diverter actuates, materials can pack in areas where the blade comes in contact with the diverter body. Over time, material buildup may occur at these points, preventing the blade from properly sealing and allowing material leakage through the diverter. To properly shift the material direction in a diverter valve, a slide gate should be installed above the diverter valve to shut off material flow prior to repositioning the blade.
When comparing an A-style and K-style diverter valve, I should first define each valve type and its components. Here are a few definitions:
- A-style diverter valve is a diverter with two symmetrical legs at equal angles from vertical. When installed into a system, the diverter will appear identical in shape to the capital-letter A.
- K-style diverter valve is a diverter that's similar in shape to the bottom portion of a capital-letter K. When installed into a system, the diverter features one vertical leg and an angled leg. The straight leg is the straight, vertical leg on a K-style diverter valve. The off leg is the angled leg on the K-style diverter valve, which normally experiences less material flow activity. This concept is often misperceived as the diverter leg that's turned off from the material flow stream. By this definition, the off leg would be subject to change almost constantly.
For both the A-style and the K-style diverter valve options, the primary responsibility is to divert material from a single source toward either of two locations. However, the application benefits for each design vary from one another.
For many applications, it's appropriate to source an A-style diverter if the manufacturing process requires diversion of similar material quantities toward each destination. Oppositely, a K-style diverter is appropriate if a process requires most material to be routed toward one destination. In typical applications, this means 70 to 90 percent of handled material is routed directly through the diverter's straight leg with the off leg handling the difference.
With A-style diverters, abrasion and wear can be a concern because as material flows through the inlet, it can make direct impact where the legs meet.
With the K-style option, material impacts where the legs meet are minimized by creating a straight-through channel. Although the K-style configuration reduces abrasion where the legs meet, it leaves the straight leg susceptible to wear because it's more regularly used.
Many diverter valve designs feature a flat blade that's thinner than the blade shaft. When handling abrasive materials, this design can create two potential problems. First, over time, each material can prematurely wear the blade shaft itself. Second, when the blade is in position to divert material, "ski jumping" of material may occur. Ski jumping is the tendency for material to roll down the blade, hit the crown of the blade shaft, and "ramp" into the diverter's sides. As material continuously abrades on the same area(s) over time, a hole will eventually be worn through the diverter body. Both the A-style and the K-style designs may be modified to address abrasion from the material handled.
Because dry bulk material characteristics can be quite different from one another, application-specific considerations must be made when selecting equipment to handle them. Neither the A-style nor K-style diverter valve can be declared universally better than the other.
It's important to consult with industry experts to analyze your unique dry bulk material handling application and select the most appropriate valve design based on features, benefits, functionality, and overall suitability for use in your system.
Vortex, Salina, KS, supplies slide gates, diverter valves, and iris diaphragms, and loadout equipment for the dry bulk industries.