Fuel Pressure

AKBill

AKBill

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AKBill
O-320-E-3D, B-19 Beech Sport. So I just changed out both of my fuel pumps, engine driven pump and electric boost pump.

Flew yesterday to test everything out. Both pumps output was the same 4psi. Flew up to 7,500ft and the fuel pressure dropped to 3psi. Limits for the engine are .5 to 6psi.

Can anyone explain this drop in fuel pressure?

Thanks
Bill B
 
Have you checked the tank vents are clear?
 
Looking at the vents they appear clear. I have not tried to run a piece of safety wire up the vent and have not tried to blow air up the vent.
 
If the vents are unrestricted, the next thing I would look for is a little air getting sucked into the fuel line somewhere.. check all the fittings are tight etc. Is it a capillary tube pressure guage or electric? If it 's a tube, bleed any air from that as well.
Other than that, I got nuthin'.
 
‘Pressure dropped to 3 psi, limit is .5 psi’? When I had my Warrior, low end in the pressure was also .5 psi.

If you are at 3, higher at times, I don’t see much reason to worry. My Warrior would drop to just a couple of psi with the electric pump off, never worried about it or had a problem. There’s always room for gauge error too.
 
sourdough44 said:
There’s always room for gauge error too.
Click to expand...
Agreed, I'm going to check the vents with a little air pressure and plumb in a separate gauge and see were that gets me. My thoughts were that fuel is not a compressible fluid and the pressure should remain constant for a given rpm and fuel flow.
 
AKBill said:
Agreed, I'm going to check the vents with a little air pressure and plumb in a separate gauge and see were that gets me. My thoughts were that fuel is not a compressible fluid and the pressure should remain constant for a given rpm and fuel flow.
Click to expand...
Interesting thought that avgas is incompressible. As vapor pressure is approached gas will get "fluffier" <-- that's a technical term.

I have no idea if the "fluffiness" matters at 7,500 feet but sorta doubt that it does particularly in cold weather.

Okay, nothing really added. Just wanted to note that fuel can get "fluffy" and Piper sez to use the boost pump if it does.
 
I suspect you did not install 2 brand new, defective (in the same way) pumps, but rather maybe your 40+ yr old gauge is not accurate???
 
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