Fuel pumps

[russ]

Anyone run 2 "EFI" fuel pumps.......in line.

Still useing 1 only, the other just sits there for emergency backup.........same fuel line tho

[Aussie_Paul]

Russ, I have run 2 efi pumps on Hybrid for around the 600 hour mark. I run them in parrallel. One is powered by the ecu and the other by a switch in the cabin.

Before starting I switch the aux puimp on to make sure that it works. I then switch it off and start the engine. If the engine starts I know the main pump is working. Then I switch the aux pump on and fly with the 2 pumps operating all the time. :yes:

Aussie Paul. :wave:

[russ]

Doin it your way.....don't it give HUGE fuel presures to the injectors etc etc. Also the amount of fuel flow threw each pump would be 50% of designed amount.....and fuel flow cools the pump yes.

Was intendin if poss, to just have the 2nd pump sitin there......in case....u know :confused:

[Aussie_Paul]

I have never had any problems at all with the above set up Russ. The fuel pressure regulator at the end of the fuel rail maintains the correct pressure at the injectors.

If you are just going to have it sit there "in case" you really need it to come on automatically with a fall in fuel pressure, otherwise you will be on the ground still trying to restart, and not sure if it is fuel pump related anyway. :yes:

Aussie Paul. :wave:

[russ]

yea.......fair enough. will give it sum more tinkin.

[redgyro]

russel,

do you think the second pump could be run paralell and opoerated buy a relay that not only has a switch in the cab for prechecks, but also by a feul low-pressure sendor that would normaly just switch on a warning light???

in a car it would be a bit like robbing/tapping into the power from a dash light [cigarette lighter] to tell a stereo to dim its screen at night when the headlights are switched on.

the relay would not need much to run and could also power the warning light the signal was originaly intended for, telling you somthing is up.

[russ]

Hey mate.........you now got me thinkin harder. Good idea thanks

[SamL]

Paul
By running the pumps in parrallel, if one failed wouldn't it also backfeed.
I run a Mechanical, and also an electric in series. I use the electric during startup to prime, then only on takeoff and landing, or low-level flying.
My 2 bob :drunk:

Sam............ :paper:

[russ]

Sam........i'm pretty sure they have 1 way valves in them, therefore back flow ai'nt possible...........i think


BTW........thanks for getting that strobe away to me......cheers

[niquenaque]

Russ, Sam,

Yes, they have to have check valves in them otherwise they would not work, they work on the same principle as a solenoid and it shuttles back and forward, so when it goes 'back', the fuel has to be stopped from flowing back into the cylinder, otherwise it wouldn't pump at all.

Whether or not - in the event of pump failure - these valves can be relied on is another matter, if one of the check valves failed then it could circulate the flow. It might be an idea t put the fuel into an accumulator with a pressure warning on it so the failure of a pump is quickly detected.

Cheers,

Nick.

[bones]

Russell, do a search on the yanky site for this(fuel pumps),as Stan the guy with the SH has put up a full wiring diagram and everything you need to have one duty pump and one pump sitting there on standby in case that one stops, it has a neat little cicut that cuts it in in under 1 second, and it keeps it on till YOU switch it back, presumable after landing.

Orrrrr and since your such an impatient prick(didnt wait 2 secs for me to reply to you last nite in the chat room) here is a link to the thread, yes i know frig im good :giggle:

http://www.rotaryforum.com/forum/showthread.php?t=9442

[Aussie_Paul]

Paul
By running the pumps in parrallel, if one failed wouldn't it also backfeed.
I run a Mechanical, and also an electric in series. I use the electric during startup to prime, then only on takeoff and landing, or low-level flying.
My 2 bob :drunk:

Sam............ :paper:


Sam, the pumps have one way valves in them. I can turn the aux off (forget to turn it on!!) :yikes:and fly for as long as I like. :yes:

Aussie Paul. :wave:

[Aussie_Paul]

Russell, do a search on the yanky site for this(fuel pumps),as Stan the guy with the SH has put up a full wiring diagram and everything you need to have one duty pump and one pump sitting there on standby in case that one stops, it has a neat little cicut that cuts it in in under 1 second, and it keeps it on till YOU switch it back, presumable after landing.

Orrrrr and since your such an impatient prick(didnt wait 2 secs for me to reply to you last nite in the chat room) here is a link to the thread, yes i know frig im good :giggle:

http://www.rotaryforum.com/forum/showthread.php?t=9442


Bones I was just about to say the same. Stans system is complicated and not KISS.

For the sake of wearing out an extra $200 pump every 10 years I reckon my system is great, BUT I am biased of course BUT I do like the KISS method. :yes:

aussie Paul. :wave:

[bones]

Bones I was just about to say the same. Stans system is complicated and not KISS.

For the sake of wearing out an extra $200 pump every 10 years I reckon my system is great, BUT I am biased of course BUT I do like the KISS method. :yes:

aussie Paul. :wave:

Paul yes it not the simplest of systems how ever after it is set up it SHOULD be trouble free, i was just throwing ideas around as he didnt seem to like the other ideas that were put forth... :yes:

[Sonnyj]

Gents
On the electronic fuel injected motor, you may run as many pumps inline as you wish, as long as they meet or exceed the engine manufactures spec.
In the end of the fuel rail, there is a fuel pressure regulator, that will dump any excess pressure, or volume of fuel, back to the tank.
In a carbed engine, you will need to ether make sure the pressure dose not exceed 4-7psi, or premature damage to the needle and seat may accure. Or install a pressure regulator, between the pump and the carb.
Installing a low pressure switch and a relay, really is pretty strait foward, any electrician or mechanic worth his salt can make it happen.
Hope that helps .
:cheers:
Sonny

[Aussie_Paul]

Installing a low pressure switch and a relay, really is pretty strait foward, any electrician or mechanic worth his salt can make it happen.



Sonny, we are talking about Russ here!!! :crazyas:

Aussie Paul. :wave:

[russ]

You'll keep ya mongrel :chuckel:

[mceagle]

I think some are confused about how an EFI system works. In a carby system the fuel pump only has to deliver enough fuel to the carby and the carby takes care of the rest. The pressure of the fuel pump is a bit irrelevant as long as it supplies enough.

In an EFI system, the injectors open for set intervals and they are not fed by a float chamber but directly by the fuel pump. The injector intervals (duration) are fixed by the computer and vary according to many factors, but not fuel pressure. The fuel pressure is a very critical part of the mixture control and this is controlled by the fuel pressure regulator at the end of the injector rail. The fuel pump must be capable of supplying a considerable amount of excess fuel under all conditions, and the excess bypasses through the regulator.
This is generally around 30 to 34 psi - higher than this and the engine runs too rich and lower than this and the engine runs too lean.
EFI pumps are capable of supplying a lot of fuel at a very high pressure so the regulator must have the capacity to return the excess otherwise the pressure can build up. There is where a problem can exist when running 2 EFI pumps. More often than not, they will supply more fuel than the regulator can handle, the pressure will build up and the engine will run too rich and use too much fuel.
I have read on the US forum that at least one manufacturer is running 2 pumps at approx 60 psi. This will work OK if you adjust the injector duration to a lot lower figure to compensate for the added pressure. The problem here is that if one pump fails, the pressure will drop considerably and the engine will run too lean causing engine failure and possible severe damage. This totally negates the reason for running 2 pumps in the first place.
Two pumps can be run successfully if the return has sufficient volume that the pressure is the same with one or two pumps on, or if the secondary pump is wired through a pressure switch to automatically activate should there be a reduction in fuel pressure. (The auxiliary pump would also be wired to a light on the dash).
For cruising altitude work, the second pump can be manually switched because there would be plenty of time to activate it and restart the engine.

There should be no concern with feed back if the pumps are installed in parallel because they are rotary positive displacement pumps with no valves, which means that fuel should not be able to flow either way if the fuel pump is not operating (except a minute amount due to running clearances).

In my opinion running 2 pumps is not necessary nowadays anyway. A single pump (of reputable brand) is more reliable than a Lycombing or Contintental, assuming that it is fitted and wired correctly. Pumps that have proven to fail (after 1000+ hours) do not fail totally but rather loose fuel pressure at the top end when demand is highest and this is noticeable as a “miss” at full throttle. The Gyro can still do many hours by avoiding full throttle if required (not recommended).

[russ]

Yea tim.........was told that just yesterday, run 1 pump, 2nd to low pressure bizo. Me man says as you say........quality pumps are mainly bullit proof, so for piece of mind.....i'm goin as stated, 1 on standby.............thanks


Side note.........me inflite adjustable prop should be here ina couple of weeks, real keen to see how these go. At $4 grand, they better be good. [ keepin in hidden, coz waddles might nick the damn thing for his flight to the nats this yr ] :yes: lucky mongrel. :peace:

[Aussie_Paul]

Points noted and agreed with Tim. However I have never had a problem with the way I had it set up. One or two pumps running the fuel flow or lamdba never varied. For training work I like to take every precaution I can. I don't want to have a problem at a height and aisrspeed that might cost me a machine. Students will do that from time to time.

The low fuel pressure switch to a relay is certainly one way to go.

Aussie Paul. :wave:

[niquenaque]

Ouch!

Blame the students then;...

Cheers,

Nick.

[redgyro]

just be carefull with a carbie.

some carbies will flood at an idle if the pumps are too higher pressure and volume. seems the float cant pull all the feul up.