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  #1  
Old 11-01-2012, 03:29 PM
Jeff R's Avatar
Jeff R Jeff R is offline
 
Join Date: Jun 2007
Location: Merritt Island, FL
Posts: 602
Default Brief super high fuel pressure

I dragged my airplane out today for a short flight this morning, running through my normal engine start checklist, and was surprised by what my boost pump did.....

I have the Airflow boost pump that I got from Van's for my IO-320. My normal start routine is full throttle and mixture, run the boost pump for a few seconds (normally get about 37 psi), boost pump off, pull out the throttle and mixture, then crank the ignition until the engine catches, then slowly add mixture and throttle as needed.

Today, things didn't sound right with the boost pump and a glance at the Dynon showed 99 psi (full scale) of fuel pressure! Then, silence. The 5 A fuse for the boost pump had blown.

I called Don at Airflow to discuss some possible things. One thing he mentioned was that I use a larger fuse (he recommended 10A). Before removing the cowling to troubleshoot, I replaced the fuse (7.5 A) and tried a normal startup again and, this time, everything was normal. I flew for a bit and cycled the boost pump on and off several times and all remained well. Pressure was normal at around 37 psi.

Temps were in the upper 60's and I only use av gas.

Any idea why I would have seen such a high pressure, and why it went away?
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Jeff Rosson
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RV14 - Working on Empennage/Tail Cone
RV9A - Completed! First flight on July 18, 2012!
Based at Merritt Island, FL (KCOI)
VAF Number: 1170


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Star Trek Quote: "Logically, it could work. Also, logically, there are a hundred variables, any one of which could put us in a worse position than we're in now." Mr. Spock in Return to Tomorrow
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  #2  
Old 11-01-2012, 03:50 PM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
Default

The AFP pump has a high-pressure relief valve, if that sticks closed or is blocked the pressure will spike. That would surely cause the motor to pull a lot more current and pop your fuse/breaker.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #3  
Old 11-01-2012, 03:57 PM
erich weaver's Avatar
erich weaver erich weaver is offline
 
Join Date: Aug 2006
Location: santa barbara, CA
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It was my understanding that the AFP pump was physically incapable of such pressures. Maybe Don can confirm this?

Also, the 37 lbs "normal" pressure seems high to me; i typically see around 26 lbs I think.

erich
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  #4  
Old 11-01-2012, 04:18 PM
Jeff R's Avatar
Jeff R Jeff R is offline
 
Join Date: Jun 2007
Location: Merritt Island, FL
Posts: 602
Default

Yes, Don said that was higher than the pump should be capable of doing. And, you are correct, my normal fuel pressure is 27 psi, not 37 psi.
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Jeff Rosson
Repeat Offender
RV14 - Working on Empennage/Tail Cone
RV9A - Completed! First flight on July 18, 2012!
Based at Merritt Island, FL (KCOI)
VAF Number: 1170


----
Star Trek Quote: "Logically, it could work. Also, logically, there are a hundred variables, any one of which could put us in a worse position than we're in now." Mr. Spock in Return to Tomorrow
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