Abstract: A coupling device for a valve arrangement includes a valve. The valve includes a valve shaft. The valve includes a first cavity, having a first shaped cross-section, extending into a portion of the valve shaft and having a first coefficient of thermal expansion (CTE). The valve includes a valve plate, having a second CTE. The valve plate includes a second cavity, having a second shaped cross-section. The valve includes a coupling device, having a third CTE, a first end having a first shaped cross-section, for engagement with the first cavity, and a second end having a second shaped cross-section for engagement with the second cavity. At a first operating temperature the coupling device will have a clearance within at least one of the first or second cavities. At a second operating temperature, the coupling device does not have clearance within the first or second cavities.