Today's Message Index:
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1. 12:11 PM - Re: High fuel pressure warning (Bubblehead)
2. 01:22 PM - Re: Re: High fuel pressure warning (mel@becknet.com)
Message 1
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| Subject: | Re: High fuel pressure warning |
BARRY CHECK 6 wrote:
> Ralph:
>
> There are a few issues that can cause this type of result.
> 1 - Restricted fuel line.
>
> 4 - Clogged filters.
>
> 6 - FUZZ floating around in the fuel distribution system.
>
>
> Story: I had the SAME high pressure reading on a friends plane
> (RV7A)... Every-time he turned on the BOOST PUMP the warning would
> sound and light would come on. As a precaution and since we were
> working on the Conditional Inspection we changed the Inline Fuel
> Filters coming out of each wing. When I did I found BOTH aluminum
> fuel lines to be crimped down. I cut off the crimped ends and
> installed a longer rubber tube to the inline fuel filters. Problem
> Solved.
>
> Barry
>
>
I deleted some text to focus on 3 or 4 items.
Barry, I am not sure I understand cause and effect on the aluminum lines being
crimped down. Those are presumably on the suction side of the engine driven pump.
How does that cause higher pressure on the discharge side of the pump?
Clogged filters or crimped lines between the tank and pump could make the pump
have to suck harder and maybe cavitate which would cause reduced pressure on the
discharge side of the pump. I can see how obstructions downstream of the pump
could cause high pressure but not an obstruction on the tank side.
Also, how were you able to isolate the problem to the fuzz in the distribution
side?
I have a lot of experience operating pumps of all kinds including similar positive
displacement pumps. I also have a ME degree and took the requisite fluids
classes. An obstruction downstream of the pump is essentially a "resistor" and
the system due to the servo is a constant flow (current in electrical terms)
system. To overcome a restriction the pump has to put out higher pressure just
as voltage might have to be increased in an electrical circuit to keep current
the same.
I think a restriction between the pump and the tank does not affect the output
pressure unless the restriction is so severe the pump cannot draw enough fuel.
If we measured pressure on the inlet side of the pump we would see lower pressure
which is needed to flow the same amount of fuel. But unless the pump is
starved for fuel, the outlet pressure will be the same as always. If the pump
does get starved outlet pressure will drop, just as it would if we ran a tank
dry.
John
--------
John
Keller, TX
RV-8 N247TD
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=467461#467461
Message 2
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| Subject: | Re: High fuel pressure warning |
Some high-wing, high-performance, single-engine GA aircraft have a fuel syst
em that features fuel injection rather than a carburetor. This system combin
es gravity flow with the use of one or two auxiliary fuel pumps positioned b
efore the fuel filter or screen. The Teledyne-Continental system is an examp
le:
-mel beckman
On Mar 19, 2017, at 12:12 PM, Bubblehead <jdalmansr@gmail.com> wrote:
com>
>
>
> BARRY CHECK 6 wrote:
>> Ralph:
>> There are a few issues that can cause this type of result.
>> 1 - Restricted fuel line.
>> 4 - Clogged filters.
>> 6 - FUZZ floating around in the fuel distribution system.
>> Story: I had the SAME high pressure reading on a friends plane
>> (RV7A)... Every-time he turned on the BOOST PUMP the warning would
>> sound and light would come on. As a precaution and since we were
>> working on the Conditional Inspection we changed the Inline Fuel
>> Filters coming out of each wing. When I did I found BOTH aluminum
>> fuel lines to be crimped down. I cut off the crimped ends and
>> installed a longer rubber tube to the inline fuel filters. Problem
>> Solved.
>> Barry
>
>
> I deleted some text to focus on 3 or 4 items.
>
> Barry, I am not sure I understand cause and effect on the aluminum lines b
eing crimped down. Those are presumably on the suction side of the engine d
riven pump. How does that cause higher pressure on the discharge side of th
e pump?
>
> Clogged filters or crimped lines between the tank and pump could make the p
ump have to suck harder and maybe cavitate which would cause reduced pressur
e on the discharge side of the pump. I can see how obstructions downstream o
f the pump could cause high pressure but not an obstruction on the tank side
.
>
> Also, how were you able to isolate the problem to the fuzz in the distribu
tion side?
>
> I have a lot of experience operating pumps of all kinds including similar p
ositive displacement pumps. I also have a ME degree and took the requisite f
luids classes. An obstruction downstream of the pump is essentially a "resi
stor" and the system due to the servo is a constant flow (current in electri
cal terms) system. To overcome a restriction the pump has to put out higher
pressure just as voltage might have to be increased in an electrical circui
t to keep current the same.
>
> I think a restriction between the pump and the tank does not affect the ou
tput pressure unless the restriction is so severe the pump cannot draw enoug
h fuel. If we measured pressure on the inlet side of the pump we would see l
ower pressure which is needed to flow the same amount of fuel. But unless t
he pump is starved for fuel, the outlet pressure will be the same as always.
If the pump does get starved outlet pressure will drop, just as it would i
f we ran a tank dry.
>
> John
>
> --------
> John
> Keller, TX
> RV-8 N247TD
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=467461#467461
>
>
>
>
>
>
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-mel beckman
> On Mar 19, 2017, at 12:12 PM, Bubblehead <jdalmansr@gmail.com> wrote:
>
com>
>
>
> BARRY CHECK 6 wrote:
>> Ralph:
>>
>> There are a few issues that can cause this type of result.
>> 1 - Restricted fuel line.
>>
>> 4 - Clogged filters.
>>
>> 6 - FUZZ floating around in the fuel distribution system.
>>
>>
>> Story: I had the SAME high pressure reading on a friends plane
>> (RV7A)... Every-time he turned on the BOOST PUMP the warning would
>> sound and light would come on. As a precaution and since we were
>> working on the Conditional Inspection we changed the Inline Fuel
>> Filters coming out of each wing. When I did I found BOTH aluminum
>> fuel lines to be crimped down. I cut off the crimped ends and
>> installed a longer rubber tube to the inline fuel filters. Problem
>> Solved.
>>
>> Barry
>
>
> I deleted some text to focus on 3 or 4 items.
>
> Barry, I am not sure I understand cause and effect on the aluminum lines b
eing crimped down. Those are presumably on the suction side of the engine d
riven pump. How does that cause higher pressure on the discharge side of th
e pump?
>
> Clogged filters or crimped lines between the tank and pump could make the p
ump have to suck harder and maybe cavitate which would cause reduced pressur
e on the discharge side of the pump. I can see how obstructions downstream o
f the pump could cause high pressure but not an obstruction on the tank side
.
>
> Also, how were you able to isolate the problem to the fuzz in the distribu
tion side?
>
> I have a lot of experience operating pumps of all kinds including similar p
ositive displacement pumps. I also have a ME degree and took the requisite f
luids classes. An obstruction downstream of the pump is essentially a "resi
stor" and the system due to the servo is a constant flow (current in electri
cal terms) system. To overcome a restriction the pump has to put out higher
pressure just as voltage might have to be increased in an electrical circui
t to keep current the same.
>
> I think a restriction between the pump and the tank does not affect the ou
tput pressure unless the restriction is so severe the pump cannot draw enoug
h fuel. If we measured pressure on the inlet side of the pump we would see l
ower pressure which is needed to flow the same amount of fuel. But unless t
he pump is starved for fuel, the outlet pressure will be the same as always.
If the pump does get starved outlet pressure will drop, just as it would i
f we ran a tank dry.
>
> John
>
> --------
> John
> Keller, TX
> RV-8 N247TD
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=467461#467461
>
>
>
>
>
>
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>
>
>
>
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