Fuel pressure high with boost pump on

[vluvelin]

Yesturday on final flipped on boost pump got alarm to check fuel.
Fuel pressure jumped to over 100 psi.
Airflow performance regulator stuck close.
O ring somehow got bigger. Replaced O ring with someething similar.
Now getting intermittent fluctuations up to 50 psi
Does anybody have part number ,size ,or place to purchase correct O ring????

On AFP wesite can not find any documents for FM-200 servo.
Can this high pressure do damage to servo?????
Maybe someone have some document like user manual and can share?..

Thank you

[Taildrgr]

Here is the text of an email I sent to Don at Airflow Performance. His contact info is at the end.


Email Quote---
When I turn on the boost pump, the pressure shoots up and over ranges the pressure sensor (>60 psi?) for a second, then drops to 25 psi.
The relief valve is sticking.

Did the temporary high pressure damage the fuel injector servo or mechanical fuel pump?


Don's response---------

This is normal for this pump as the relief valve poppet seats into an O-ring. This may be more prevalent depending on the type and brand of fuel that is used and if the pump has been sitting idle for some time. The poppet may stick a bit in the O-ring when the pump is first turned on. We have a different material O-ring for applications using alcohol which may not swell as much as the O-ring that is installed in the normal boost pump assemblies. I can send you a different O-ring if you provide me a mailing address. You will not damage the pump or the fuel control with pressures at 60 PSI.


Don Rivera
Airflow Performance
111 Airflow Drive
Spartanburg, SC 29306
Phone: 864-576-4512
Fax: 864-576-0201
E-Mail: don@airflowperformance.com
Web: www.airflowperformance.com

End quote--------------

[DanH]

Gentlemen, just to clarify, are you having this problem with the old style pump assembly....




...or the new style pump assembly?

[Taildrgr]

My pump is the old style.

[vluvelin]

Yes
Looks like picture 1 old stile

It was no problem with high pressure or sticking regulator before
Allways used 100LL

[DanH]

Old style...ok, that's useful info.

Be aware that the dual diaphragm operating scheme of an Airflow Performance or Bendix type fuel control makes them insensitive to inlet fuel pressure. Put another way, the pump pressure regulator can stick, but it's not likely to make any difference in the way the engine runs.

Not much worry about damage either. The normal fuel pressure operating range for an Airflow FM-200 is given as 20-90 psig. The Precision Silver Hawk (same basic operating principle) is 20~50 nominal, max operating 80, and a momentary pressure max of 140 psig.

[vluvelin]

Thank you Dan

[Taildrgr]

Thanks for the feedback, Dan.

Do not want to hijack the thread, but here is some additional info for those that may have a similar situation:

My pump had sat dry for 3 years before first engine start. The check valve stuck on the first use each time I used the pump and subsequent uses were ok within the same engine run period. After the pump sat for a few days, it would stick again on the first use.

However, on the second flight, it worked fine with no pressure spike on initial use. Have not flown since, but maybe the valve has loosened up by now.

Note that each time after the check valve becomes unstuck, the fuel pressure is steady at 26 psi with the pump on, 24 psi with the pump off.

[airguy]

Reviving this thread, I have had E-10 premium autofuel in my fuel system for about 2 months now and had clean forgotten about this potential O-ring issue. Last night I ran my engine to check a few things before my airworthiness inspection, and both pumps (old-style) briefly touched 60psig on initial run, which caught my attention. Apparently 2 months of exposure was enough to cause some swelling and sticking of the pressure relief valve, I have sent an email to Don Rivera for the replacement material O-rings.

Just a data point to consider.

[vluvelin]

Not in my case my fuel system don't see any other fuel then 100LL

You should check fuel pressure sensor that could be issue on its own
When my O ring got stuck I could hear fuel pump change its sound