- 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.
- 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.
- 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.
- 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.
The Butterfly Valve Alternative
Because of its low profile design, the Vortex Orifice Gate serves as a good alternative to a butterfly valve. The fundamental difference is that the Orifice Gate is designed specifically to handle dry materials. The gate utilises a stainless steel rectangular plate with a circle opening machined through the center of it. This machined plate slides open and closed between two compression-loaded hard polymer plates.
In the closed position, the compression load on the blade prevents material and conveying air from escaping through the valve and into the plant’s atmosphere. In the open position, the circle opening in the blade aligns with the conveying line, thus eliminating flow obstructions or exposed seals that might be vulnerable to wear and tear from the material flow stream.
To ensure a positive seal, the valve “self-cleans” material from the seat on each stroke of the blade so there is no bridging or packing of material. The Orifice Gate’s hard polymer seals compensate for wear unlike the softer seals in a butterfly valve. The seals are also adjustable without removing the valve from service thus reducing downtime and added costs.
This article appeared as the cover story for the June 2015 issue of Bulk Solids Today.