This type of valve utilizes a machined housing and end plates and an internal “plug” (typically aluminum due to weight considerations) with two machined, stainless steel ports. The seal between the housing and plug is typically Polyurethane and is not in the material flow path. While the design and construction of this valve is far superior to any of the valved mentioned, the high cost associated with this type of valve limits its use except for extreme conditions (e.g. dense phase conveying, highly degradable materials, etc).