Narrative:

We had flown for 2 days in juarez, mexico and refueled our 15 gallon stainless steel tanks (30 gallons) in mexico. The next day we flew in carlsbad, NM, and the vapor flow through the orifice in the pilot head would stop when fuel pressure was below 90 psi. Normally, vaporization and flow occurs all the way to zero pressure in the fuel manifold. I disassembled the upper and lower converter body -- removed the shuttle and found a syrup or tar-like substance fouling the top o-ring and restricting the operation of the converter shuttle. I cleaned the converter chamber and dried the o-ring. The vapor flow operated normally all the way down to 5 psi on the fuel manifold gauge, but the restriction recurred on my later flts. I finally had to replace the top o-ring because the syrup caused it to swell (or possibly the cleaning materials I used), and the shuttle would not operate until it was replaced. Eventually, the condition ended -- possibly the 'syrup' was used up or flushed from the system. But I have heard mr X, an aerostar repair station in dallas, tx, talk about ethyl mercaptan. Now I periodically pressurize my fuel manifold -- turn off the fuel supply -- then start the fuel flow through the liquid pilot light. I monitor the gauge pressure and, if the flow through the pilot light stops before the gauge reads zero, then I know there is something restricting the movement of the converter shuttle. My personal limit is 30 psi (unpublished or approved standard or method) before I disassemble and clean the shuttle, o-ring and converter body. I use 30 psi as an arbitrary figure because it is 1/2 of 60 psi -- the minimum fuel pressure flight operations. Callback conversation with reporter revealed the following information: the reporter believe that the contamination is strictly excess ethyl mercaptan and nothing else. He also states that many other aeronauts in his area have had the same sort of problem. A call to a balloon repair station local to the ASRS found that this problem has never been seen here. The local balloon repairman flies the same equipment that the reporter has. The local repairman tends to agree with this humble aeronaut/analyst that the problem most likely is due to contamination problems at the refinery in tx or mexico, not to an excess of ethyl mercaptan. The reporter decries the lack of any national standard for the amount of ethyl mercaptan that is put into propane.

Related reports:

Google
 

Original NASA ASRS Text

Title: FUEL CONTAMINATION.

Narrative: WE HAD FLOWN FOR 2 DAYS IN JUAREZ, MEXICO AND REFUELED OUR 15 GALLON STAINLESS STEEL TANKS (30 GALLONS) IN MEXICO. THE NEXT DAY WE FLEW IN CARLSBAD, NM, AND THE VAPOR FLOW THROUGH THE ORIFICE IN THE PILOT HEAD WOULD STOP WHEN FUEL PRESSURE WAS BELOW 90 PSI. NORMALLY, VAPORIZATION AND FLOW OCCURS ALL THE WAY TO ZERO PRESSURE IN THE FUEL MANIFOLD. I DISASSEMBLED THE UPPER AND LOWER CONVERTER BODY -- REMOVED THE SHUTTLE AND FOUND A SYRUP OR TAR-LIKE SUBSTANCE FOULING THE TOP O-RING AND RESTRICTING THE OP OF THE CONVERTER SHUTTLE. I CLEANED THE CONVERTER CHAMBER AND DRIED THE O-RING. THE VAPOR FLOW OPERATED NORMALLY ALL THE WAY DOWN TO 5 PSI ON THE FUEL MANIFOLD GAUGE, BUT THE RESTRICTION RECURRED ON MY LATER FLTS. I FINALLY HAD TO REPLACE THE TOP O-RING BECAUSE THE SYRUP CAUSED IT TO SWELL (OR POSSIBLY THE CLEANING MATERIALS I USED), AND THE SHUTTLE WOULD NOT OPERATE UNTIL IT WAS REPLACED. EVENTUALLY, THE CONDITION ENDED -- POSSIBLY THE 'SYRUP' WAS USED UP OR FLUSHED FROM THE SYS. BUT I HAVE HEARD MR X, AN AEROSTAR REPAIR STATION IN DALLAS, TX, TALK ABOUT ETHYL MERCAPTAN. NOW I PERIODICALLY PRESSURIZE MY FUEL MANIFOLD -- TURN OFF THE FUEL SUPPLY -- THEN START THE FUEL FLOW THROUGH THE LIQUID PILOT LIGHT. I MONITOR THE GAUGE PRESSURE AND, IF THE FLOW THROUGH THE PILOT LIGHT STOPS BEFORE THE GAUGE READS ZERO, THEN I KNOW THERE IS SOMETHING RESTRICTING THE MOVEMENT OF THE CONVERTER SHUTTLE. MY PERSONAL LIMIT IS 30 PSI (UNPUBLISHED OR APPROVED STANDARD OR METHOD) BEFORE I DISASSEMBLE AND CLEAN THE SHUTTLE, O-RING AND CONVERTER BODY. I USE 30 PSI AS AN ARBITRARY FIGURE BECAUSE IT IS 1/2 OF 60 PSI -- THE MINIMUM FUEL PRESSURE FLT OPS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR BELIEVE THAT THE CONTAMINATION IS STRICTLY EXCESS ETHYL MERCAPTAN AND NOTHING ELSE. HE ALSO STATES THAT MANY OTHER AERONAUTS IN HIS AREA HAVE HAD THE SAME SORT OF PROB. A CALL TO A BALLOON REPAIR STATION LCL TO THE ASRS FOUND THAT THIS PROB HAS NEVER BEEN SEEN HERE. THE LCL BALLOON REPAIRMAN FLIES THE SAME EQUIP THAT THE RPTR HAS. THE LCL REPAIRMAN TENDS TO AGREE WITH THIS HUMBLE AERONAUT/ANALYST THAT THE PROB MOST LIKELY IS DUE TO CONTAMINATION PROBS AT THE REFINERY IN TX OR MEXICO, NOT TO AN EXCESS OF ETHYL MERCAPTAN. THE RPTR DECRIES THE LACK OF ANY NATIONAL STANDARD FOR THE AMOUNT OF ETHYL MERCAPTAN THAT IS PUT INTO PROPANE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.