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Fuel Pump Switch(es)
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kkinney

Joined: 11 Jan 2006
Posts: 42

Posted: Sat Sep 09, 2006 7:18 am Post subject: Fuel Pump Switch(es)

I'm planning a left/right fuel system each with an on/off valve and an aux pump on each incoming line.

I'm thinking of using an on/off/on switch for pumps rather than an on/off switch for each pump.



Can anyone offer any thoughts on the downside of this?



Regards,

Kevin Kinney



--

Non-parent - I don't see how you can raise children & stay sane.

Parent - You don't.  You pick one and go with it.

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Sat Sep 09, 2006 12:40 pm Post subject: Fuel Pump Switch(es)

Kevin;



One downside is "single point of failure". If the switch fails you loose

both pumps. Also, if one pump fails and blows the fuse you loose both pumps.

Two switches allows two fuses, two circuits, redundancy.



Bob McC

---

_________________
Bob McC
Falco #908
(just starting)

frank.hinde(at)hp.com
Guest

Posted: Sat Sep 09, 2006 5:43 pm Post subject: Fuel Pump Switch(es)

Sure!.. if the single point of failure (namely the

switch)...er...fails...You crash!



If you are dependant on those electric pumps (like I am) always wire

them seperatly all the way back to the battery...If you have two

batteries make sure they are isolated and feed one pump from each

battery.



Frank RV7a, IO360 electic pump in each wing root. No mechanical pump,

single Odyssey and dual alternator.



Flying as of yesterday.



--

FLYaDIVE(at)aol.com
Guest

Posted: Sun Sep 10, 2006 3:42 am Post subject: Fuel Pump Switch(es)

In a message dated 9/9/06 11:21:44 AM Eastern Daylight Time, kkinney(at)fuse.net 

writes:



 	  Quote: 	
		   

  

  I'm planning a left/right fuel system each with an on/off valve and an aux 

 pump on each incoming line.

  I'm thinking of using an on/off/on switch for pumps rather than an on/off 

 switch for each pump.

  

  Can anyone offer any thoughts on the downside of this?

  

  Regards,

  Kevin Kinney

=========================
	


WHY!



Kevin:



There are thousands of planes out there with a ONE PUMP boost system running 

off on the one common line going to the engine or from the fuel selector.  

What I would do though is put a fuel filter on each tank.  And then if you want 

to go crazy put in a parallel boost pump.  That will give you redundancy and of 

course more weight and maintenance. 



Barry

"Chop'd Liver"



"Show them the first time, correct them the second time, kick them the third 

time." 

Yamashiada

aerobubba(at)earthlink.ne
Guest

Posted: Sun Sep 10, 2006 6:00 am Post subject: Fuel Pump Switch(es)

Hi Kevin-

 

 	  Quote: 	
		  I'm planning a left/right fuel system each with an on/off valve and an aux

pump
	


 	  Quote: 	
		  on each incoming line.

I'm thinking of using an on/off/on switch for pumps rather than an on/off

switch
	


 	  Quote: 	
		  for each pump.

 
	


 	  Quote: 	
		  Can anyone offer any thoughts on the downside of this?

 
	


Yup, there are a few.  Other folks have touched on most of them already. 

The fusing issue could be handled by either putting the FP fuses downstream

of a SPDT center off switch with a larger fuse at the bus (for a total of

3), or by using a DPDT center off switch and two feeds from 2 fuses at the

bus(ses).  The former arrangement would have the single feed wire, the

connectors at each end, the big fuse at the bus, and the switch itself as

'single point of failure' nodes.  The latter arrangement would reduce the

single point of failure nodes to just the switch itself, rather than all

the other stuff .  The most bullet proof system would indeed involve

separate switches for the individual pumps, which would ideally be fed by

separate busses.  On balance, having one fuse, one feed wire, and one

switch controlling two pumps leaves you with no less redundancy than my

single pump system, and actually has a smidge more.  Unless, of course,

your pumps are inherently less reliable than mine.  I have no info on that,

tho-



Having typed this all out, and considering that the electric fuel pumps are

already a back up for the mechanical pump, I'd personally stick with the

single electric pump solution.  Especially if one only had one bus to draw

power from.  If you are committed to two pumps, I'd probably be perfectly

happy with the single switch, three fuse arrangement.  Two electric fuel

pumps gets into the 'belts and suspenders' zone, and complete independent

power systems seems to get into the 'belt, suspenders, and duct tape' zone.



As ever, this is worth precisely what you've paid for it-



glen matejcek

aerobubba(at)earthlink.net

brian-av(at)lloyd.com
Guest

Posted: Sun Sep 10, 2006 9:59 am Post subject: Fuel Pump Switch(es)

On Sun, 2006-09-10 at 04:41, FLYaDIVE(at)aol.com wrote:

 	  Quote: 	
		   >  I'm planning a left/right fuel system each with an on/off valve and an aux 

 > pump on each incoming line.

 >  I'm thinking of using an on/off/on switch for pumps rather than an on/off 

 > switch for each pump.

 >  

 >  Can anyone offer any thoughts on the downside of this?

Kevin, I think your approach is just fine. Yes, the switch is a

single-point-of-failure but it shouldn't cause your engine to stop

running as the engine-driven fuel pump should be able to keep the engine

running. To lose the engine you would have to lose the both halves of

the switch, both electric fuel pumps, and the engine driven fuel pump.

 	  Quote: 	
		   There are thousands of planes out there with a ONE PUMP boost system running 

 off on the one common line going to the engine or from the fuel selector.  

 What I would do though is put a fuel filter on each tank.  And then if you want 

 to go crazy put in a parallel boost pump.  That will give you redundancy and of 

 course more weight and maintenance. 

Barry, I think Kevin's idea of two pumps, each right at the tank, is a

good one. That approach means that your boost pump is never having to

suck against a fuel line thus reducing the chance for vapor lock to

almost zero. (I have experienced a vapor lock in flight on the

engine-driven fuel pump. It gets your attention.) If he is thinking of

running mogas, this might be a very good idea. Most automotive systems

now immerse the fuel pump right in the fuel. This ensures that the pump

has prime and that there is no chance for vapor lock.

Brian Lloyd

George McNutt

Joined: 09 Jan 2006
Posts: 30

Posted: Sun Sep 10, 2006 1:19 pm Post subject: Fuel Pump Switch(es)

Kevin,  aside from the on/off switch debate, an on/off valve on each 

tank introduces problems and complexity into emergency procedures for a 

fuel delivery interruption. For example if you had a blockage or 

inadvertently ran a tank dry you will have to reposition two fuel 

valves, presumably on opposite sides of the cockpit.

Also check valves may be required to prevent  fuel transfer if both tank 

valves were inadvertently left open?



George in Langley BC



Kevin Kinney wrote:

 	  Quote: 	
		   



 I'm planning a left/right fuel system each with an on/off valve and an aux pump on each incoming line.

 I'm thinking of using an on/off/on switch for pumps rather than an on/off switch for each pump.



 Can anyone offer any thoughts on the downside of this?



 Regards,

 Kevin Kinney

frank.hinde(at)hp.com
Guest

Posted: Sun Sep 10, 2006 6:38 pm Post subject: Fuel Pump Switch(es)

I have an electric pump in each wing root and NO mechanical pump...I

assumed this system was the same but if it has a mechanical pump then

sure a single switch would be just fine.



Frank 



--

frank.hinde(at)hp.com
Guest

Posted: Sun Sep 10, 2006 6:40 pm Post subject: Fuel Pump Switch(es)

On my electric only system I simply switch pumps to switch tanks...No

selector valve...Just a non return valve in each line joining to a tee

then up to the standards vans selector that has been plumbed to act as

an on-off valve.



The valve has 4 ports so its simple to configure it this way.



System has now flown a total of 2.8 hours...



Frank



7a



--

brian-av(at)lloyd.com
Guest

Posted: Sun Sep 10, 2006 8:24 pm Post subject: Fuel Pump Switch(es)

On Sep 10, 2006, at 7:39 PM, Hinde, Frank George (Corvallis) wrote:



 	  Quote: 	
		   

 (Corvallis)" <frank.hinde(at)hp.com>



 On my electric only system I simply switch pumps to switch tanks...No

 selector valve...Just a non return valve in each line joining to a tee

 then up to the standards vans selector that has been plumbed to act as

 an on-off valve.


	


My only concern with that would be that a pump failure could render  

1/2 your fuel unavailable. Several aircraft have been lost on long  

over-water flights when electric transfer pumps have failed thus  

rendering necessary fuel unavailable. Something to think about.



Brian Lloyd                         361 Catterline Way

brian HYPHEN av AT lloyd DOT com    Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

Gilles.Thesee(at)ac-greno
Guest

Posted: Mon Sep 11, 2006 12:23 am Post subject: Fuel Pump Switch(es)

Hi all,



 	  Quote: 	
		  >

> On my electric only system I simply switch pumps to switch tanks...No

> selector valve...Just a non return valve in each line joining to a tee

> then up to the standards vans selector that has been plumbed to act as

> an on-off valve.

I had to design a fuel circuit for an electrically dependant engine :  
	


in order to achieve true redundancy I had to run each pump from a 

separate battery. The main pump runs from the main battery, and is on 

whenever the mags are "on". The boost pump runs from the auxiliary 

battery, and has a switch. The fuel valve works the normal way. For the 

pilot, everything works as in a engine with mechanical pump.

No single electric failure can deprive the engine of its fuel supply.



A schematic of my setup can be seen at

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

(Scroll down to the bottom of the page)



FWIW

Regards,

Gilles Thesee

Grenoble, France

http://contrails.free.fr

frank.hinde(at)hp.com
Guest

Posted: Mon Sep 11, 2006 5:52 am Post subject: Fuel Pump Switch(es)

Absolutely correct Brian,



That is the one downside I came up with too. Basically you have to allow a small reserve in each tank, For normal flying that means 0.5 hours in each tank...For out in the badlands that might be a bit more...



Frank 



--

aerobubba(at)earthlink.ne
Guest

Posted: Mon Sep 11, 2006 6:45 am Post subject: Fuel Pump Switch(es)

George / Kevin-

 

George- "... an on/off valve on each 

tank introduces problems and complexity..." 



Boy, am I glad you wrote that!  I completely missed the part about

independent fuel valves.  Kevin, besides all the good points George makes,

and as someone pointed out a while back on one of these lists, you will

only find a "BOTH" position on a fuel selector in a high wing single engine

airplane.  The low wing planes have left, right, and off.  With a high wing

plane, you will sometimes see quite an imbalance develop when drawing fuel

from both tanks simultaneously, even with the head pressure caused by the

tank location.  This effect could be much greater in a low wing

installation.  If you had the ability to have both tanks plumbed to the

engine at the same time, when one tank emptied you could suck air into the

system.  Obviously, this would not be good. I would definitely recommend

against two fuel valves.



Sorry for not catching that sooner-



glen matejcek

aerobubba(at)earthlink.net

oldbob(at)BeechOwners.com
Guest

Posted: Mon Sep 11, 2006 7:27 am Post subject: Fuel Pump Switch(es)

Good Morning Frank,



I've been away for a few days and am just catching up

on my E-mail so I have not yet digested this thread.

However, the following statement piques my curiosity.



"Basically you have to allow a small reserve in each

tank, For normal flying that means 0.5 hours 

in each tank...For out in the badlands that might be a

bit more..."



Would you mean by this statement that you do not want

to run a tank dry or that you feel it is actually

dangerous to do so?



May I ask what sort of an engine is being fed and why

you feel the need for it to never be allowed to run

dry?



Many light aircraft, both certified and experimental,

have multiple fuel tanks. Some Bonanzas have six

separate fuel tanks.  If a half hours worth of fuel is

to be considered unusable in each tank, a lot of

payload and range is being lost.



The vast majority of commonly used light plane engines

are driving a solidly connected propellor that will

windmill quite well following a loss of fuel flow.  I

understand that some of the experimental airplanes do

have propellors that will declutch or otherwise not

drive the engine if power is lost, but that is not

true of most.



Running a fuel tank dry is a very viable fuel

management operation if it is done correctly.



Any more information or thoughts you would care to

mention?



Happy Skies,



Old Bob

AKA

Bob Siegfried

Stearman N3977A

Downers Grove, IL

LL22



 

--- "Hinde, Frank George (Corvallis)"

<frank.hinde(at)hp.com> wrote:



[quote] 

 Frank George (Corvallis)" <frank.hinde(at)hp.com>

 

 Absolutely correct Brian,

 

 That is the one downside I came up with too.

 Basically you have to allow a small reserve in each

 tank, For normal flying that means 0.5 hours in each

 tank...For out in the badlands that might be a bit

 more...

 

 Frank 

 

 --

frank.hinde(at)hp.com
Guest

Posted: Mon Sep 11, 2006 7:30 am Post subject: Fuel Pump Switch(es)

Well that depends.



On a carbed engine it does not matter if you run a tank dry with Both

tanks feeding the engine.



The pump that draws air will simply airlock and cease to pump

anything...It can't pump against the other pump that is pumping fuel.

Secondly...even if the pump did pump air it simply gets flushed out of

the float bowl in the carb.



I have proved this over 400 hours in my last airplane.



In my new FI'd airplane, Getting air to the servo would not be great but

I really doubt the pump will pump any air against the 30 psi made by the

other pump...I haven't tried to prove this yet. 

The really neat thing about this install is that you can even lose all

the fuel out of one tank on take off, plug a fuel filter etc, and the

engine will still run normaly.



Frank



--

brian-av(at)lloyd.com
Guest

Posted: Mon Sep 11, 2006 7:46 am Post subject: Fuel Pump Switch(es)

On Sep 11, 2006, at 7:43 AM, glen matejcek wrote:



 	  Quote: 	
		   airplane.  The low wing planes have left, right, and off.  With a  

 high wing

 plane, you will sometimes see quite an imbalance develop when  

 drawing fuel

 from both tanks simultaneously, even with the head pressure caused  

 by the

 tank location.  This effect could be much greater in a low wing

 installation.


	


The Nanchang CJ6A and Yak-52 both are low-wing airplanes with a  

single on/off fuel selector. The wing tanks gravity feed to a header  

tank at the low point in the fuselage. The header tank feeds the carb  

through a manual wobble pump, the firewall fuel shut-off, and the  

engine-driven fuel pump. All three tanks share a common vent. The  

header tank has small flapper valves to prevent fuel from flowing  

back out to a tank.



Many complain of uneven fuel feed but I have found that keeping the  

ball in the center solves the problem. And even if you do get a  

substantial imbalance, getting the ball back into the center causes  

the fuel to feed from the more-full tank. It seems to work pretty well.



Brian Lloyd                         361 Catterline Way

brian HYPHEN av AT lloyd DOT com    Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

Bill Denton

Joined: 10 Jan 2006
Posts: 97
Location: Chicago, IL USA

Posted: Mon Sep 11, 2006 7:57 am Post subject: Re: Fuel Pump Switch(es)

 	  aerobubba(at)earthlink.ne wrote: 	
		  George / Kevin-

 

George- "... an on/off valve on each 

tank introduces problems and complexity..." 



Boy, am I glad you wrote that!  I completely missed the part about

independent fuel valves.  Kevin, besides all the good points George makes,

and as someone pointed out a while back on one of these lists, you will

only find a "BOTH" position on a fuel selector in a high wing single engine

airplane.  The low wing planes have left, right, and off.  With a high wing

plane, you will sometimes see quite an imbalance develop when drawing fuel

from both tanks simultaneously, even with the head pressure caused by the

tank location.  This effect could be much greater in a low wing

installation.  If you had the ability to have both tanks plumbed to the

engine at the same time, when one tank emptied you could suck air into the

system.  Obviously, this would not be good. I would definitely recommend

against two fuel valves.



Sorry for not catching that sooner-



glen matejcek

aerobubba(at)earthlink.net 	




RE: Kevin, besides all the good points George makes, 

and as someone pointed out a while back on one of these lists, you will 

only find a "BOTH" position on a fuel selector in a high wing single engine 

airplane.



JFTR: New Cessna 172's have a Left/Right/Both fuel selector

frank.hinde(at)hp.com
Guest

Posted: Mon Sep 11, 2006 8:12 am Post subject: Fuel Pump Switch(es)

See below....



--

brian-av(at)lloyd.com
Guest

Posted: Mon Sep 11, 2006 12:37 pm Post subject: Fuel Pump Switch(es)

On Mon, 2006-09-11 at 08:57, Bill Denton wrote:

 	  Quote: 	
		   RE: Kevin, besides all the good points George makes, 

 and as someone pointed out a while back on one of these lists, you will 

 only find a "BOTH" position on a fuel selector in a high wing single engine 

 airplane.


	


Well, it is probably not safe to use the words "always", "never", and

"only" when describing systems. As I pointed out earlier, both the

Nanchang CJ6A and Yak-52 are low-wing aircraft that have only an on/off

fuel selector at the firewall. There is no way on either of these

aircraft to select a left or right tank. They are always on "both".



Brian Lloyd

martorious(at)charter.net
Guest

Posted: Mon Sep 11, 2006 2:22 pm Post subject: Fuel Pump Switch(es)

Bob, I think the reason he wanted to leave a reserve in each tank is in case

the fuel pump in the opposite tank quit and he was therefore denied access

to the fuel in that tank he would have the reserve fuel in the 'good' tank.

Marty



--

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