Design and Analysis of a Fan Outlet Check Valve for the Exploration Portable Life Support System

Check valves are required at the outlets of NASA’s Exploration Portable Life Support System (xPLSS) ventilation loop fans to permit forward flow through the ventilation loop while preventing backflow through the fans when they are not running. These check valves must maintain full specified functionality at all orientations in gravitational environments ranging from weightlessness to full terrestrial gravity. A check valve design has been developed to satisfy the above requirements via an iterative process combining mechanical design, computational fluid dynamics (CFD) analysis, Thermal Desktop® analysis, and static force analysis. The initial design concept was a flapper valve in which a mass-balanced flapper freely rotates from fully closed (0°) to a 45° angle, after which a torsional spring engages the flapper to prevent it from opening beyond the point at which reverse flow cannot close the valve. Analysis results, however, indicated that the magnitude of reverse flow induced during contingency purge operations would not always be sufficient to overcome gravitational and frictional moments to close the flapper in its unassisted, free-rotating range. The design was thus revised to provide spring engagement throughout the entire span of valve positions, removing the flapper’s dependency on reverse flow for valve closure. Since commercially-available torsion springs are too stiff for this application, the revised design uses a linear compression spring that engages the flapper at an offset from the flapper’s pivot point. CFD and static force analyses were used to determine acceptable design parameters, from which valve geometry and spring selection were determined.