Fuel system tec tips
 

HI all, today I mixed my 50 gallons of kero, as I do each year. This time I bought a 10 micron filter and pump.
The first thing I noticed, after I set up the system with the filter on the suction side, I could never stop the air bubbles, so I put the filter downstream of the pump, and worked great.After the first 15 gallons went through, I thought I should add another small filter on the suction side, a new pump and all, did not want to wreck a new pump. Well guess what, air bubbles again, and no matter what you did to the oriantation of the small filter, their was air bubbles.
Conclusion, Jetcat and Jet Central say install the fuel filter , down stream of the pump, they are right, never install a filter on the suction side, the filter ,actually separates the air from the fuel.
I also noticed the static electricity formed at the filter. look at the second pic of the hair on my arm, and then when I move my arm close to the filter, see the hair stand up.
Rcpete

RE: Fuel system tec tips
 

I do not agree.
IMHO your photos show that you have an airleak.


The before/after pump matters when you use festo cause there nature is to seal with presure and not suction.
The jetcat metal silver filter doesnt care if goes before or after ...just to be on the corect direction placed on the system


I always prime my system with the help of the pump at high power before conect it to the engine(just conect it back to the UAT)...and knocking the filter till i see no air coming in the lines..


sorry for my english

RE: Fuel system tec tips
 

Yeah, I get hair days like that too.

Lucky Pierre

RE: Fuel system tec tips
 

Tell me MR Greese, how is it that their is air bubbles in the small filter and fuel line, before the pump, yet you remove the one piece sealed filter on the suction side and their is no air bubbles in the line between the small filter and pump.
And by the way, where did you get the idea , I was useing Festo fitting, do you see Festo fittings, Their are no festo Fitting.
Rcpete

RE: Fuel system tec tips
 

Hi Pete,

I can't tell from the photos for sure, but is the flow in the small filter as follows:
- in through the inlet port to region outside the filter paper
- through the filter paper to the center core of the assembly
- out the inlet port

Regards,

Jim

RE: Fuel system tec tips
 

If the filter is been primed well, then an airleak maybe?


I didnt mean you use.I sed when its been used.

RE: Fuel system tec tips
 

Hey Pete I allways thought that the filter after the pump was for stopping small pieces of pump wear from the valves and turbine?



Frank

RE: Fuel system tec tips
 

Do you mean that there is air in the kyro? [:-]My UAT is full after many runs and you can say thats a filter before pump..

cheers

RE: Fuel system tec tips
 

It's not air in the filter. The pump is causing low pressure in the filter and the kero is flashing off into vapor. Once the flow slows the pressure rises and the vapor recondences into kero. Mine does it all the time...no leaks.

Mike

RE: Fuel system tec tips
 

HI, I was waiting for some one to say that, same principal as in central air conditioning, reduce the pressure and the liquid flashes off to gas.
So far, I have tested the PST air trap,and have flashing off at 27 oz."s per minute, I'll have to go to a smaller pump to see when it stops.
I would like to see manufactures rate their UAT's/Air traps in maximum flow rate before the Kero flashes.
Rcpete
PS, thanks Mike

RE: Fuel system tec tips
 

That too, u don't want a bit of fuel pump causing your fuel velve to stick open. That's one ticket to a fire.

But Pete's absolutely right about the air coming out of suspension in the fuel if there's enough suction.

If you've ever been a scuba diver and understand what's going on there, then think of this as your fuel system getting "the bends".

RE: Fuel system tec tips
 

Kero has air entrained in it. Lower the pressure such as creating poor inlet conditions on a pump, and you will find air bubbles. Give them a place to collect like that filter housing and you've got air....

What does seem strange is that the filter size seems pretty generous for that pump size, and yet the results are pretty dramatic. I would more expect to see milky colored kero and not copious quantities of air.

RE: Fuel system tec tips
 

I have been flying AMT turbines since 2000, Mercury, Mercury HP, Pegasus, Pegasus SP, and AMT 400 all air start all installed with the same fuel supply arrangement as per manual from first Mercury manual in 2000, I have NEVER EVER had an inflight flameout on any one of them, but I do have an interesting bullet list that are absolutes in EVERY model setup concerning fuel management for me.

I dont care where pump is mounted from turbine, I generally have the pump in the tip of the nose as it weighs so much and use it as primary ballast for CG.

I always use 4mm rigid tygon as a one piece hose from PUMP to TURBINE longest run near 30" (it is ALWAYS solid fuel and never has air no matter length of storage time.)

I always use 6mm rigid tygon from BVM UAT to a Festo 6mm filter, then a 6mm Festo manual shutoff, then to the Fuel pump inlet. (it is ALWAYS solid fuel and never has air no matter length of storage time.)

I always use MIL Spec JP4 Norgren flex tubing of 3/16" ID to make all tank interconnects to the UAT barb, I have jets that used a single tank, to 5 tanks.

When setting up the tanks the final overflow(s) have proven the fuel flow restriction, as part of the debug process, I use 7.2VDC to power my fuel jug pump and do fills and defuels of fuel system through the UAT fill barb and observe the bulge and compression of the BVM UAT sidewalls, and adjust size of final tank vent outlet to correct for minimal movement during this fueling and defueling.

End of day IIMHO see that the 3/16" fuel line ID and a STOCK BVM UAT provides plenty of fuel flow for up to 40lb thrust, as evidenced by the end of flight shutdown process that shows AVG pump volts to range from 3.1 VDC on the Mercury to 4.8VDC on the AMT 400

.02

RE: Fuel system tec tips
 

Mike, thats an interesting point, I have made a new range of UAT's called CAT's (composite air traps) Olivier is testing them all and will publish finding in Jetpower magasine, also RCJI are doing a piece to by Colin Strauss.

I will see if its something that can be looked at, I certainly have been very keen to make the fittings and all tube, bores as large as possible within the designs so restrictions etc are minimised.

The three items being tested....

marcs

RE: Fuel system tec tips
 

No there is not any air to be separate in the kyro. rcpete thought it was air but it is just vaporized kyro

RE: Fuel system tec tips
 

That is an interesting theory.

It should be remembered that no matter what size the UAT is , the pressure differiential between atmosphere and the inside of the fuel system, is dependant upon the ENTIRE fuel system upstream of the pump. In other words you need to ensure that the entire fuel system is sized correctly, right from the, breather to the pump.

I think that the problem that many people have had with UATs collapsing, is not because the UAT is too small, but the ENTIRE fuel system has created too much pressure drop. This manifests itself when the UAT collapses, because the UAT is the most flexible part in the system, and is close to the pump, where the maximum negative pressure is.. Small fuel lines, and tank fittings with small orifices need to be avoided, especially in a high flow fuel systems..


Roger

RE: Fuel system tec tips
 

I just place my fuel vents to look forward.

RE: Fuel system tec tips
 

George do i have promblem if my fuel vents don't look forward?

RE: Fuel system tec tips
 

i dont think so my friend....i just like to place vents looking forward so the litle extra presure helps the fuel system in flight..
.. some people place vents looking aft and they see fuel after there flight unter there plane.http://en.wikipedia.org/wiki/Venturi_effect



p.s. very good job you have done there!

RE: Fuel system tec tips
 

Thanks George.Last sunday i flew my DF f-80 again.Look at
http://www.youtube.com/user/ARGYPILATUS?feature=mhee

RE: Fuel system tec tips
 

"I think that the problem that many people have had with UATs collapsing, is not because the UAT is too small, but the ENTIRE fuel system has created too much pressure drop. This manifests itself when the UAT collapses, because the UAT is the most flexible part in the system, and is close to the pump, where the maximum negative pressure is.. Small fuel lines, and tank fittings with small orifices need to be avoided, especially in a high flow fuel systems.. "

DITTO.......

Thats what I find in my new systems and the Nalgene UAT bottle is the perfect monitor, I was concerned the 1/8" ID brass fittings/clunks in my tank setups would not allow enough fuel to run the AMT 400 when I swapped it out for a Pegasus setup jet, but they were plenty. even when the AVG pump volts after flight changed by over 1.2VDc to 4.8VDC, versus 3.6VDC.

I do find it interesting that 1/8" brass fitting ID's is plenty for 40lbs thrust and the final vent line size has been the ultimate culprit and first place I start, The worst thing is when final tanks are in parrellel and then a T used to vent them together, that T and final vent line needs to be 5/16"+ ID........

RE: Fuel system tec tips
 

At 750mph you get a full 1.45 psi....

RE: Fuel system tec tips
 

Yes there is. Kero is aerophile. About 10% in volume.
The suction creates cavitation. The first part of cavitation is actually diluted air that come out into bubbles. When depression increases, then you get vaporized kero.
Please refer to my fuel article, published 2 months ago.

RE: Fuel system tec tips
 

[:o] Kero is aerophile???........"A lover of aviation" What does that mean?

Tailwinds,

John

RE: Fuel system tec tips
 

No John. Greek etymology. aer- and -philos

http://www.etymonline.com/index.php?term=aero-
http://www.etymonline.com/index.php?term=-phile