Re: PA28-181 Fuel pressure drop off - Inspired by the Gascolotor thread.
- From: "Roy Page" <g4dyr*Removethisantispamstuff*@earthlink.net>
- Date: Tue, 27 Sep 2005 23:47:31 GMT
Well Kyle that is a pretty convincing explanation.
I will take a another look at the service manual and follow your arguments
for myself.
If you are correct, and I am not doubting you, I am on my way to solving the
problem.
Thanks again
Roy
"Kyle Boatright" <kboatright1@xxxxxxxxxxx> wrote in message
news:RfadnTxITNy4UqTeRVn-sw@xxxxxxxxxxxxxx
>
> "Roy Page" <g4dyr*Removethisantispamstuff*@earthlink.net> wrote in message
> news:0Nb_e.4922$QE1.117@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>I bought our Piper Archer [PA28-181] just over a year ago from a
>>Californian owner and flew it home to it's new base in Ohio.
>> On the flight home, we noticed on long climbs that the fuel pressure fell
>> off from an indicated mid scale reading to about one third scale.
>> In level cruise the indicated pressure returned to mid scale.
>> Although we took the top cowl off at every stop to check carefully that
>> we still had all the important bits still hanging on, we failed to notice
>> that the gascolator had a slight fuel leak until a few days after we got
>> the bird home.
>> You need to remove the lower cowl to get access to the gascolator.
>> Our A&P put a new bowl seal on the gascolator which cured the leak and
>> appeared to cure the fuel pressure changes.
>> A few months passed and then occasionally I noticed a slight fall off in
>> fuel pressure when climbing.
>> I concluded that the mechanical engine driven fuel pump must be getting
>> tired and, to be safe, replaced it with a new pump three weeks ago.
>> No change, the fuel pressure still falls off when climbing and returns to
>> mid scale in level cruise.
>>
>> I also belong to the Taylorcraft Flying Club
>> www.taylorcraftflyingclub.org.
>> The club, these days, flies a fleet of three PA28's.
>> Our PA28-180 has a similar fall off in fuel pressure when climbing.
>>
>> Ideas please ?
>>
>> Roy
>> N5804F
>
> Here's one...
>
> The pressure transducer in your airplane may not have a large enough vent
> port, which causes a false low fuel pressure reading when you climb and a
> false high pressure reading as you descend. The transducer vents to
> ambient air, so it can compare the internal (fuel) pressure to the ambient
> (reference) conditions and arrive at the difference. That difference is
> "fuel pressure".
>
> If the vent port on the transducer is undersized (and they ARE small), or
> if it is partially clogged, its reference pressure is off. If you're
> climbing, the transducer thinks the reference pressure is higher it than
> it actually is, because the higher pressure air inside the transducer's
> reference side hasn't equalized to ambient. Therefore, it compares the
> internal (fuel) pressure with the reference pressure and sees a smaller
> difference than expected. That plays out as a low fuel pressure reading.
> When you descend after being at altitude, the reference pressure is low
> (because you were at a higher altitude where the air pressure is lower),
> and the transducer compares the actual pressure with a low reference
> number, and, volia - high fuel pressure reading.
>
> I saw the same thing in 300 hours of flying my Tomahawk, and see it again
> in my RV-6.
>
> KB
>
>
>
.
- References:
- PA28-181 Fuel pressure drop off - Inspired by the Gascolotor thread.
- From: Roy Page
- Re: PA28-181 Fuel pressure drop off - Inspired by the Gascolotor thread.
- From: Kyle Boatright
- PA28-181 Fuel pressure drop off - Inspired by the Gascolotor thread.
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