REG NASA-LLIS-0497-1997 Lessons Learned - Propulsion Valve Contamination Sources in Vendor Test Facilities (1995).pdf

1、Lessons Learned Entry: 0497Lesson Info:a71 Lesson Number: 0497a71 Lesson Date: 1997-03-13a71 Submitting Organization: JPLa71 Submitted by: C. GuernseySubject: Propulsion Valve Contamination Sources in Vendor Test Facilities (1995) Abstract: The Cassini/Mars Global Surveyor thruster high pressure lat

2、ch valve was redesigned to use a Kel-F seal instead of Teflon. Because the harder plastic has less ability to seal around small particles, particulate contamination in the helium gas can cause random leakage. Use high purity helium for pressure testing and for flight consumables, and establish conta

3、mination control procedures.Description of Driving Event: During thermal cycle test of the Cassini/Mars Global Surveyor thruster high pressure latch valve - the final test in the valve qualification program - an unacceptable rate of valve leakage was detected. Disassembly of the valve revealed parti

4、culate and hydrocarbon contamination. Examination of the vendor test fixture disclosed that the 4000 psi test pressure had been attained using a compressor that included a non-operational, contaminated “cold trap.“ Under these conditions, the room temperature test permitted compressor oil to contami

5、nate the valve assembly allowing accumulation of debris on the valve seat.The valve seat had been redesigned during the Cassini project to use a Kel-F seal instead of Teflon. A harder plastic able to withstand higher pressure and temperature than Teflon, Kel-F has less ability to conform and seal ar

6、ound small particles.Cleaning and reassembling the test article was only partially successful in stopping leakage during a second thermal cycle test. It was the consensus that this hard Kel-F plastic seal is subject to random leakage due to particulate contamination in the helium gas used in test an

7、d in flight.Reference(s):Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Cassini PFR B33135a71 Contractor memo no. 1.3-TM-237, “High Pressure Latch Valve Qualification Closure“, June 11, 1996.Lesson(s) Learned: 1. Propulsion system valve designs

8、remain vulnerable to gas leakage over the course of multi-year missions.2. Hard plastic seals such as Kel-F are nearly as sensitive to contamination as metal-to-metal seals.3. Examine propulsion valve vendor test facilities for sources of potential test article contamination-particularly by hydrocar

9、bons.4. Establish contamination control procedures for qualification test of propulsion valves. Flush the test article with freon to remove any hydrocarbon deposits. As part of these procedures, the qualification valve should be subjected to at least 5 times as many mechanical/thermal cycles as expe

10、cted in flight without detecting excessive leakage.5. Establish contamination control procedures for both flight hardware and ground support equipment. Use high purity (medical application) helium for pressure testing and for flight consumables.Recommendation(s): N/AEvidence of Recurrence Control Ef

11、fectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Parts Materials & Processesa71 Spacecrafta71 Test ArticleProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 1997-03-25a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-