REG NASA-LLIS-0471-1995 Lessons Learned - Contamination from Failures caused by Fluid Filters - Scout Program.pdf

1、Lessons Learned Entry: 0471Lesson Info:a71 Lesson Number: 0471a71 Lesson Date: 1995-06-13a71 Submitting Organization: LERCa71 Submitted by: Judy TerlepSubject: Contamination from Failures caused by Fluid Filters - Scout Program Description of Driving Event: A number of H2O2 motor valves in the H2O2

2、fuel system of the Scout Missile experienced leakage due to contamination of the valves 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 contam

3、ination exposed particles larger than 20 micron. Each valve was protected at the fuel inlet by a 15-20 micron filter.An extensive failure investigation discovered that the contamination was being induced by the stainless steel filter itself.Fabrication of the filter was accomplished by press fitting

4、 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

5、 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.Lesson(s) Learned: Fluid filters can be a source of contamination if they are dirty or fail structurally

6、.Recommendation(s): 1. Perform a high pressure flush on safety-critical filters prior to their addition into a system.2. Avoid manufacturing processes which can damage filters during fabrication.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Evidenc

7、e of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1996-11-01a71 Approval Name: Sell Jamesa71 Approval Organization: 501-4a71 Approval Phone Number: 216-433-8618Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-