1. Not Designed for Dry Material
Butterfly valves are not designed to handle dry bulk solids. They were designed for gas and liquid applications. The abrasiveness of dry bulk solids erodes away on butterfly valves to the point where they no longer properly seal and need to be replaced.
2. Disk Impedes Material Flow Stream
The butterfly valve design places the valve’s disc right in the middle of the material flow stream in pneumatic conveying and gravity applications. This can create a significant flow restriction and many engineers design the entire conveying system with larger piping to accommodate this blockage in the valve.
3. Difficulty Displacing Dry Materials
The soft seals of a butterfly valve can promote another problem. The soft seals allow the disc or blade to produce a bubble-tight seal when located in the closed position. Due to the characteristics of dry solids, the material cannot be displaced like a gas or liquid. Overtime, the constant opening and closing will cause the seals erode and tear. Eventually, this will prevent the butterfly valve from creating a tight seal.
4. Soft Seals are Exposed to Material
The seals on a butterfly valve is also susceptible to blast abrasion from the material flow stream. This is not an issue when handling gas and liquids. But with dry bulk solids, this causes additional wear points and eventual leakage of material and/or conveying pressure through the valve, even when the valve is in the closed position. In a powder handling application, particles tend to migrate through the stem of the butterfly valve causing the valve to seize.