In zero offset butterfly valves, also known as concentric butterfly valves, the stem passes through the centreline of the disc that is cantered in the seat; all of this is cantered inside the valve body. The valve body, seat, and disc lie concentrically when it is in a closed position. The disc rotates on the central axis; this allows a 360° rotation. In a fully-opened position, the flow is divided into two halves on each side of the disc, which is now parallel to the flow. The advantage of this type is that the flowing media does not come in contact with the valve body because the seat is covering it.
Zero offset butterfly valves feature resilient soft seats, which rely on the flexibility and deformation of the seat to ensure a seal. During operation, the disc edges slide against the seat, creating significant friction that can shorten the valve’s lifespan. Due to the use of polymeric or elastomeric materials for the seat, these valves are generally suited for lower pressure and temperature conditions.
Zero offset butterfly valves are commonly used in pipelines for liquids and gases with maximum pressure ratings of 250 psi and temperature limits of up to 400°F.