NASA-LLIS-0471

Abstract

<strong>Description of Driving Event:</strong> <br>A number of H2O2 motor valves in the H2O2 fuel system of the Scout Missile experienced leakage due to contamination of the valve's teflon seats. Failed parts analysis revealed minute stainless steel particles embedded in the teflon seats. This contamination prevented complete closure at the poppet to seat interface. Examination of the contamination exposed particles larger than 20 micron. Each valve was protected at the fuel inlet by a 15-20 micron filter. <br>An extensive failure investigation discovered that the contamination was being induced by the stainless steel filter itself. <br>Fabrication of the filter was accomplished by press fitting an inner ring into a larger diameter ring after inserting the meshed screen circular filter. This technique essentially sandwiched the screen between the two rings. Bi-sectioning of several filters revealed that the frayed ends of the meshed filters screen were being temporarily trapped between the rings. Subsequent high pressure fuel flows usage dislodged the particles and the resultant contamination. Since the contamination was being released behind the filter, the filter was ineffective.