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Secondary Fuel Pump, correct or not

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craigb(at)onthenet.com.au
Guest

Posted: Sat Dec 08, 2007 5:12 pm Post subject: Secondary Fuel Pump, correct or not

[quote]   Just a thought, but are we    all doing our backup fuel pumps incorrectly????

   Someone mentioned to me the    other day, what if, the main pump fails in such a

   way as to totally block the    system. Would the backup pump be able to push the fuel

   past the blockage? I guess    probably not. Should we not be paralleling the main pump,    with

   a non return valve after    each pump, so pressure is not lost back through the other    pump.

   I realise the convention is    to series the pumps, to "lift" the fuel to the main pump,    but

   is the convention correct,    or is this giving us all a false sense of security.

    

   Just a    thought.

    

   craig

    

[b]

josok-e(at)ukolo.fi
Guest

Posted: Sun Dec 09, 2007 1:10 am Post subject: Secondary Fuel Pump, correct or not

Craigh,

The Rotax and factories fuel circuit diagrams call for he pumps to be in series, with non-return valves parellel to the pumps. 

In that diagram a blocked fuel pump will be bypassed by a valve. I can not think of any single component failure that would prevent fuel to be passed to the engine. 



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

josok-e(at)ukolo.fi
Guest

Posted: Sun Dec 09, 2007 3:50 pm Post subject: Secondary Fuel Pump, correct or not

Hi Ron,



How do you calculate that? Valve one open? Pump 2 will supply. Valve one closed? Pump one will supply. Valve 2 open?  Pump one supply, Valve 2 blocked, pump 2 will supply. The same logic counts for the pumps as well. Please explain where the scenario goes wrong. 

It does not matter if the pump is mechanically or electrically driven.  



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

rparigor(at)suffolk.lib.n
Guest

Posted: Sun Dec 09, 2007 6:41 pm Post subject: Secondary Fuel Pump, correct or not

Hi Jos



"How do you calculate that?" (failure because of failed Andair 1 way

valve)



I will first mention that my 1988 R100GS BMW motorcycle with type 64 Bing

Carbs has a vacuum controlled valve that turns off fuel to carbs when

there is no vacuum. Let bike sit with MoGas with Stabil (fuel stablizer)

(with carbs run dry) and that valve glues itself closed! Valve is not too

unlike the Andair 1 way valves used by Europa on 914. A very light

pressure to open when working correctly, but 100PSI will not open if glued

shut. Carb cleaner and air can unstick, but almost unbelievable how it can

get so stuck. I have not heard of Andair 1 ways sticking opened or closed,

but my dart throw is sticking closed with MoGas use and sitting plane is

good possible failure.



OK here are some failures Europa 914 series with bypass and 2 filters (or

2 gasculators)**:

**Glue both valves shut, pump #1 on will have a hard time getting through

#2 pump that is off or failed (if both pumps on and they are working will

run OK)

**Glue both valves shut, if #1 pump fails or is off or #1 filter or

gasculator clogged, #2 pump will not provide

**#2 pump fails or is off and #1 valve stuck opened no fuel flow from pump

#1 will be supplied

**#1 pump fails or is off and #2 valve opened no flow from pump #2 will be

supplied



After fooling with system:

http://contrails.free.fr/engine_914_fuel_syst_test_en.php



Good idea to use P1 as primary pump, and good idea to be able to turn off

P1 and run just P2 to test system. If wired so P1 always running you could

not really test #1 valve or #2 filter or Gasculator.



I am using 2 Andair gasculators instead of supplied filters:

http://www.europaowners.org/modules.php?set_albumName=Begin-06-2003&op=modload&name=gallery&file=index&include=view_album.php

See:

Album: 914 modular fuel system. Series with bypass, two Andair 375s.



Another very real failure is having an air leak in Gasculator or Filter!

On my system if I pushed up on one of the beautiful Stainless Steel Andair

bowl drains, just the tiniest bit, either pump #1, or #2 or both #1+#2

would far rather suck air than fuel and foam right away! Thats right, does

not matter Gasculator #1 valve or Gasculator #2 valve, a small leak will

kill fuel flow! Although nice drain, it still relies on an O-Ring to seal.

Worth a very close look before flight no fuel is leaking from those

Gasculator drains, and very careful monitor you have differential pressure

on both pumps, checking 1 pump at a time at high MP.



As one of my tests was to see and touch and feel for my self how the pumps

will perform with a suction head. I noticed that if you create a very

small air leak at either of the Gasculators, it is far more devistating

the greater the suction head. In other words full fuel and nose not too

high will be nowhere near as hard as low fuel level and high nose.



Ron P.

josok-e(at)ukolo.fi
Guest

Posted: Mon Dec 10, 2007 12:58 am Post subject: Secondary Fuel Pump, correct or not

Hi Ron,

Thanks for the amount of explanation, you are correct: If And If brings you down. No fuel left also. 

However, i specifically mentioned

"any single component failure"

because there always seem to be people who manage to improve the scenario. 

Did you forget to read that? 



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

rparigor(at)suffolk.lib.n
Guest

Posted: Mon Dec 10, 2007 7:19 am Post subject: Secondary Fuel Pump, correct or not

Hi Jos



"any single component failure"



**Air leaking at valve #1 could be same as air into a Gasculator or filter

and shut you down



**Having Series with bypass, a single air leak at either of the

Gasculators or filter will shut you down, if you had parallel pumps with a

gasculator or filter on intake this is not the case



I like Series with bypass better than parallel pumps, the Europa series

with bypass like better than Rotax series with bypass because it uses a

second filter or in my case gasculator. True if you wanted to go crazy you

could add another 1 way between filters or gasculators and negate an air

leak at #2 Gasculator from interfering with #1 Gasculator, but not worth

the extra parts count. 



I did read "any single component failure" and figured this is not an FAA

test where you must choose a letter for an absolute answer, but wanted to

make sure anyone using or considering series with bypass understands its

operation, not just "B" is the correct answer to question #2.



Sincerely

Ron Parigoris

air.guerner(at)wanadoo.fr
Guest

Posted: Mon Dec 10, 2007 10:07 am Post subject: Secondary Fuel Pump, correct or not

"On my system if I pushed up on one of the beautiful  Stainless Steel Andair

bowl drains, just the tiniest bit, either pump #1, or  #2 or both #1+#2

would far rather suck air than fuel"

  

  

 Ron,

  I have to disagree with that.  If your  fuel pumps are installed below the bagage bay as instructed by Europa, they will  always be below the fuel level, unless your tank is almost empty. Therefore,  unless there is an obstruction at the tank output coarse filter, the  pressure inside the gascolator, upstream of the filter, will always be higher  than the ambiant pressure. So if your fuel drain leaks, it will not suck air but  will leak fuel to the outside.    

 Regards

 Remi

    [quote][b]

rparigor(at)suffolk.lib.n
Guest

Posted: Mon Dec 10, 2007 11:25 am Post subject: Secondary Fuel Pump, correct or not

Hi Remi



"If your fuel pumps are installed below the baggage bay as instructed by

Europa, they will always be below the fuel level, unless your tank is

almost empty."



My Fuel 914 pumps are mounted below baggage bay area. Lets raise the

Gasculators to the top of the cockpit for 1 minute. As long as no air is

in line and there are no  air leaks, it is true if the fuel level is above

the inlet of the fuel pump it will be OK, but if you open the drain, air

will be pulled in and air not fuel will be sucked in easier than fuel. Now

lets move the Gasculator to where I have it, right on the floor of fuse

aft of the baggage bay ribs, you need fuel level above the outlet of the

Gasculators to not let a leak in the drain cause grief. Granted for most

part it will not be a problem, but you can pretty easily get level I feel

can be critical if you get an air leak, nose low during landing with low

fuel, running on main of tank and right hand pattern would put outlet of

Gasculator above fuel level.



I am not trying to scare anyone, just keep in mind that a leak in fuel

filter or Gasculator drain besides being a bad thing to leak fuel, could

cause problems with fuel delivery. I want to make light that the

Gasculator drain has more of a chance of leaking than a filter and that

although chances of actually having your engine play  Silent Night because

of a air leak is low, none the less at least be aware that drain or drains

can introduce air, so if you see a leak at all, fix it.



The little Pierburg fuel pumps create quite a squirt. There is no question

that even if you had fuel level slightly above gasculator outlet (which is

at the same height as inlet) you will be putting entire feed upstream of

the inlet of the fuel pump at a slight negative pressure. I fooled with

placing pick up of fuel close to surface of fuel, and it creates a

whirlwind and sucks in air. I tried it with level a little above

Gasculators and below.



Try drinking through a straw that has a mini hole in it your favorite

beverage very fast with level of liquid slightly higher than your mouth.

Especially at full power, the Pierburg/s can just about provide the

pressure needed to crack Fuel Pressure regulator and just a little

reserve. If Wastegate gets stuck and you go over max boost, crack pressure

will not be reached and motor will quit, then less boost, fill carbs and

get power back until it quits again. Introduce not much air at full

throttle and I suspect crack pressure will not be met with a proper

functioning wastegate. Just this little tiny bit of air plays hell with

pumps ability, it cavitates and pressure goes way down.



Go ahead, lift up tail of your plane next time you need fuel and turn on

pump and open drain a little, then holding drain same amount opened have

someone turn off pump. 



Please report your findings.



Ron P.

craigb(at)onthenet.com.au
Guest

Posted: Tue Dec 11, 2007 3:25 am Post subject: Secondary Fuel Pump, correct or not

I guess i asked a good question here, Based on the too-ing and frow-ing

here i plan to stick with my original plan to parallel the system as far as

the engine, that way both pumps and gascolators can be tested and known to

be

working correctly, with flow sufficient to run the engine from either side

(main and reserve)



craig



--

hurstkr(at)redzone.com.au
Guest

Posted: Tue Dec 11, 2007 4:45 am Post subject: Secondary Fuel Pump, correct or not

Hello Ron,



You said :-

 	  Quote: 	
		  Granted for most part it will not be a problem, but you can pretty easily

 get level I feel can be critical if you get an air leak, nose low during

 landing with low fuel, running on main of tank and right hand pattern

 would put outlet of Gasculator above fuel level.


	


At the risk of sounding pedantic, what is the significance of your reference 

to the "right hand pattern" ?



I suspect you are saying that because you are turning to the right, the fuel 

will move away from the fuel pick up in the tank ?

This will only happen if the turn is not balanced.  A slipping turn to the 

right will have the same effect as a skidding turn to the left and vice 

versa as far as the fuel movement goes.

It the turn is balanced, irrespective of the direction of turn, the fuel 

will stay in the same place as when flying with wings level.



Cheers

Kingsley

josok-e(at)ukolo.fi
Guest

Posted: Tue Dec 11, 2007 10:44 am Post subject: Secondary Fuel Pump, correct or not

Craig,

For checking the fuel system i added fuel flow sensors in both feed and return line, and the matronix controller to see fuel flow on the Dynon (or any other fuel flow meter). Extra is a switch that takes the return flow sensor out of the equation. The result on the fuel flow meter is the netto throughput of the system. Part of the checklist is to check that switch and see that the fuel exceeds 120 liters per minute on each pump, and increases with 2 pumps. Any malfunction or blockage will show up, taking the guessing out before flight. 



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

roger(at)middlecave.plus.
Guest

Posted: Tue Dec 11, 2007 11:41 am Post subject: Secondary Fuel Pump, correct or not

I missed some of the correspondence on this subject, so I hope the following

is not repetitious:-



On the 914 engine, Rotax originally specified that the two electric pumps

should be in parallel.  This was changed some years ago to the pumps being

in series.  The reason for this is that two pumps both running in parallel

can produce more flow than the regulator can cope with, and the pressure can

then rise above the limit for the carburettors.  With the pumps in series,

the volume of flow will be substantially the same with either one or both

pumps running (the pumps being more or less fixed displacement type).



Regards,

Roger Bull



--

Gilles.Thesee(at)ac-greno
Guest

Posted: Tue Dec 11, 2007 11:54 am Post subject: Secondary Fuel Pump, correct or not

Roger Bull a écrit :

 	  Quote: 	
		   The reason for this is that two pumps both running in parallel

 can produce more flow than the regulator can cope with, and the pressure can

 then rise above the limit for the carburettors.  With the pumps in series,

 the volume of flow will be substantially the same with either one or both

 pumps running (the pumps being more or less fixed displacement type).

   

Roger,
	




Did you get this information through a reliable Rotax channel ?

I was under the impression that Rotax had followed one of the Pierburg 

drawing, but failed to include check valves like is advisable in any 

parallel setup. The peculiar new Rotax "series/parallel" setup seems a 

variation on another Pierburg schematic.

Concerning the the flow with two pumps in parallel and regulator, the 

measurements we took did not show the problem you are referring to.



Some info at

http://contrails.free.fr/engine_pierburg_en.php



FWIW,

Best regards,

-- 

Gilles

http://contrails.free.fr

jrgowing(at)bigpond.net.a
Guest

Posted: Tue Dec 11, 2007 12:48 pm Post subject: Secondary Fuel Pump, correct or not

K

YOu are right on to it!

JR

---

rparigor(at)suffolk.lib.n
Guest

Posted: Tue Dec 11, 2007 3:13 pm Post subject: Secondary Fuel Pump, correct or not

Hi Kingsley



"At the risk of sounding pedantic, what is the significance of your

reference to the "right hand pattern" ?"



I was trying to make a point that all can be well till a certain scenario

is met (raise Gasculator in relation to fuel level).



My Gasculators are behind the baggage bay bulkheads. Lower the nose with

flaps down as you would when landing and that would raise the Gasculators

in relation to fuel level. I mentioned right hand pattern, it is true if

you are in a bank coordinated Gs will be vertical, when getting into bank

if you didn't apply enough rudder and slipped a bit fuel would slosh a bit

lower than Gasculators. I remember early on in my flying that I had a

tendency to not boot enough rudder when flying a right pattern (and could

in fact uncover right tank pick up). 



Ron P.

rparigor(at)suffolk.lib.n
Guest

Posted: Tue Dec 11, 2007 3:21 pm Post subject: Secondary Fuel Pump, correct or not

Hi Jos



"For checking the fuel system i added fuel flow sensors in both feed and

return line, and the matronix controller to see fuel flow on the Dynon (or

any other fuel flow meter). Extra is a switch that takes the return flow

sensor out of the equation. The result on the fuel flow meter is the netto

throughput of the system. Part of the checklist is to check that switch

and see that the fuel exceeds 120 liters per minute on each pump, and

increases with 2 pumps. Any malfunction or blockage will show up, taking

the guessing out before flight."



Boy with 120 liter per minute flow (7,200 liters per hour), you could

shoot some fuel out the back for jet assisted take offs 



I have not tested flow with fuel pressure regulator attached, but did put

restriction on outlet and with 2 pumps running, series with bypass, there

was only perhaps a small increase in flow, but there was an increase in

pressure (thumb on outlet was the instrument used).



What sort of % increase in flow are you seeing with 2 pumps running

compared to 1 running on your system??



Did you actually put diaphragm of fuel pressure regulator under pressure

as described in Rotax manual to simulate boost in airbox and lower

atmospheric pressure and measure that differential pressure (carb fuel

pressure above airbox pressure by approx. 2 to 5 PSI) and found that a

flow on ground of at least 120 liters per hour will satisfy? 



If not what is significance to 120 liters per hour on 914??



Ron Parigoris

rparigor(at)suffolk.lib.n
Guest

Posted: Tue Dec 11, 2007 3:37 pm Post subject: Secondary Fuel Pump, correct or not

Hi Gilles



"Concerning the the flow with two pumps in parallel and regulator, the

measurements we took did not show the problem you are referring to.

(differential pressure going above 5 PSI)"



Are the measurements you took differential pressure (carb fuel pressure

over airbox pressure) under worst case scenario for measuring too high a

pressure? Low manifold pressure and thick air? (in other words, not

simulating high altitude and high manifold pressure which is a test to

insure you have enough differential pressure).



Ron P.

josok-e(at)ukolo.fi
Guest

Posted: Wed Dec 12, 2007 1:47 am Post subject: Secondary Fuel Pump, correct or not

Ron,



Obvious mistake: I should have said liters per hour, not minutes. 



The fuel flow test does not test the flow to the engine, it tests the total flow out of the tank. While it is a good indication of the condition of filters and pumps, it does not test the fuel pressure regulator. For fuel pressure over air box i have the UMA sensor. 

Based on a few years of reading of accident reports and forums, i think that this total flow check before take-off would have grabbed almost all of the fuel starvation mishaps caused by clogged restrainers, filters and rotten fuel lines. If there has been any mishap with the fuel pressure regulator, i have missed it. 

Leaking connections i have had, both a damaged o-ring on the gascolator, and a poor flange on the alu pipe near the fuel selector. While these caused a hell of a smell, and some fuel under the plane, the fuel test was still over 120 liters, and over 135 liters with 2 pumps on.

Those numbers are based on my "clean" system, to have a repeatable test. Different systems will produce different throughput, and also the battery condition is a factor.  



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

rparigor(at)suffolk.lib.n
Guest

Posted: Wed Dec 12, 2007 11:34 am Post subject: Secondary Fuel Pump, correct or not

Hi Jos



"over 120 liters, and over 135 liters with 2 pumps on."



This is probably very close to what I tested.



I have a UMA differential gauge, and a UMA fuel flow gauge. I asked Ed if

he could give me a switch to read just outgoing sender on my analogue

display, but was not cost feasible.



I think you have a nice feature being able to read total flow one pump at

a time and both pumps.



To make total flow number mean more, you could do a couple of tests:

Go to full power on 1 pump, then turn off fuel selector, a little bit at a

time till you see differential pressure needle begin to go down, and below

2PSI and note your fuel flow.

Would be nice to see difference between lower and higher altitude.



If you don't mind sharing these results it would be greatly appreciated.



The fuel pressure regulator has a built in restriction. You need to meet

the required flow rate that will create enough pressure because of this

restriction to crack open the regulator and allow fuel to flow into the

carb float bowls. Each system will be slightly different due to execution

of system. 



You have the opportunity to learn what this flow rate is at various

altitudes (thin air, high boost most flow rate will be needed because

motor is gobbling up some flow, and you need higher regulator pressure

when boosting and since you are trying to overcome airbox pressure that is

absolute, when ambient pressure lowers, you need more regulator pressure

compared to higher ambient pressure).



Ron Parigoris

josok-e(at)ukolo.fi
Guest

Posted: Thu Dec 13, 2007 1:27 am Post subject: Secondary Fuel Pump, correct or not

Hi Ron,



"To make total flow number mean more"

Sorry, no, i don't think i could learn any more from that experiment. If the restricted fuel flow as in your proposed experiment drops below the fuel into the carbs, the pressure will drop. Rotax supplies that figure in the doc. It's known as fuel consumption at various power levels. On top of that, i will never experiment with vital functions of the plane in flight. It's pulling the devil at his tail 



Regards,



Jos Okhuijsen

Visit -  www.EuropaOwners.org

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