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jpx(at)qenesis.com
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 Posted: Mon Nov 16, 2009 9:11 am Post subject: Fuel pump control |
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I just came across a notation I made quite a while ago, after noticing
a neat idea, probably on this list.
It utilizes a low pressure switch to provide an "automatic" mode to
the electric fuel boost pump, so that if the engine driven pump
failed, the electric one would be powered up.
This seemed like a great idea at the time. It would likely mean an
engine hiccup, followed by the fuel pump on LED illuminating - much
better than the pilot conjecturing the engine failure is due to fuel
starvation and manually turning on the pump (would be a checklist item).
However, looking at the schematic as I drew it, as soon as the
electric pump provided sufficient pressure, the low pressure switch
would open and the pump would shut off, and then back on, and then
off. Ooops 
Is it worth fabricating a little latching circuit to provide this
automatic operation, or better to keep things simple ?
I don't do hard IFR, and manually turning on the fuel pump switch in
most circumstances would be sufficient to avoid an unpleasant landing.
Thoughts ?
Jeff Page
Dream Aircraft Tundra #10
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harley(at)AgelessWings.co
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| Posted: Mon Nov 16, 2009 9:27 am Post subject: Fuel pump control |
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Instead of a pressure switch, how about a flow switch on the input side of the mechanical pump...
Harley
Jeff Page wrote: [quote]--> AeroElectric-List message posted by: "Jeff Page" <jpx(at)qenesis.com> (jpx(at)qenesis.com)
I just came across a notation I made quite a while ago, after noticing a neat idea, probably on this list.
It utilizes a low pressure switch to provide an "automatic" mode to the electric fuel boost pump, so that if the engine driven pump failed, the electric one would be powered up.
This seemed like a great idea at the time. It would likely mean an engine hiccup, followed by the fuel pump on LED illuminating - much better than the pilot conjecturing the engine failure is due to fuel starvation and manually turning on the pump (would be a checklist item).
However, looking at the schematic as I drew it, as soon as the electric pump provided sufficient pressure, the low pressure switch would open and the pump would shut off, and then back on, and then off. Ooops
Is it worth fabricating a little latching circuit to provide this automatic operation, or better to keep things simple ?
I don't do hard IFR, and manually turning on the fuel pump switch in most circumstances would be sufficient to avoid an unpleasant landing.
Thoughts ?
Jeff Page
Dream Aircraft Tundra #10
[b]
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bob(at)bob-white.com
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| Posted: Mon Nov 16, 2009 9:44 am Post subject: Fuel pump control |
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Hi Jeff,
Another option would be to put a one way valve in the output of the
engine driven pump. T the two lines together after the valve. I think
some of the electric pumps provide a one way flow, but if not, you
would need one there also to prevent the mechanical pump from bypassing
the engine. I seem to recall a Faucet pump I had would flow backwards
sometimes depending on where it stopped when it was turned off.
Bob W.
On Mon, 16 Nov 2009 12:09:41 -0500
"Jeff Page" <jpx(at)qenesis.com> wrote:
| Quote: |
I just came across a notation I made quite a while ago, after noticing
a neat idea, probably on this list.
It utilizes a low pressure switch to provide an "automatic" mode to
the electric fuel boost pump, so that if the engine driven pump
failed, the electric one would be powered up.
This seemed like a great idea at the time. It would likely mean an
engine hiccup, followed by the fuel pump on LED illuminating - much
better than the pilot conjecturing the engine failure is due to fuel
starvation and manually turning on the pump (would be a checklist item).
However, looking at the schematic as I drew it, as soon as the
electric pump provided sufficient pressure, the low pressure switch
would open and the pump would shut off, and then back on, and then
off. Ooops
Is it worth fabricating a little latching circuit to provide this
automatic operation, or better to keep things simple ?
I don't do hard IFR, and manually turning on the fuel pump switch in
most circumstances would be sufficient to avoid an unpleasant landing.
Thoughts ?
Jeff Page
Dream Aircraft Tundra #10
|
--
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
Now Rotary Powered Alpine
http://www.youtube.com/watch?v=FwceNc2ydN8
Cables for your rotary installation - http://roblinstores.com/
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wschertz(at)comcast.net
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| Posted: Mon Nov 16, 2009 9:45 am Post subject: Fuel pump control |
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I thought perehileon design had a circuit for doing this, but in looking at there web site, I couldn't find it. Eric Jones monitors the list -- Eric?
Bill Schertz
---
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SteveR
Joined: 10 Jan 2006
Posts: 226
Location: Aledo, TX
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| Posted: Mon Nov 16, 2009 11:35 am Post subject: Fuel pump control |
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It is pretty simple to do this if you use a fuel pump and relay coil
that require the same voltage. Use a pressure sensor to control the
relay. Connect the relay output to the fuel pump AND to the relay
coil (input). That way when the fuel pump comes on (due to a low
pressure signal), the relay locks itself on, regardless of the state
of the pressure sensor. To turn the pump off, you would have a
momentary switch in the circuit that would break the connection to the
relay coil. This used to be called a "seal-in" circuit for industrial
controls.
Steve Ruse
| Quote: | Jeff Page wrote:
I just came across a notation I made quite a while ago, after
noticing a neat idea, probably on this list.
It utilizes a low pressure switch to provide an "automatic" mode to
the electric fuel boost pump, so that if the engine driven pump
failed, the electric one would be powered up.
This seemed like a great idea at the time. It would likely mean an
engine hiccup, followed by the fuel pump on LED illuminating - much
better than the pilot conjecturing the engine failure is due to fuel
starvation and manually turning on the pump (would be a checklist
item).
However, looking at the schematic as I drew it, as soon as the
electric pump provided sufficient pressure, the low pressure switch
would open and the pump would shut off, and then back on, and then
off. Ooops
Is it worth fabricating a little latching circuit to provide this
automatic operation, or better to keep things simple ?
I don't do hard IFR, and manually turning on the fuel pump switch in
most circumstances would be sufficient to avoid an unpleasant
landing.
Thoughts ?
Jeff Page
Dream Aircraft Tundra #10
|
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kuffel(at)cyberport.net
Guest
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| Posted: Mon Nov 16, 2009 11:55 am Post subject: Fuel pump control |
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Jeff,
<< low pressure switch to provide an "automatic" mode to the electric fuel boost pump, so that if the engine driven pump failed, the electric one would be powered up. ... It would likely mean an engine hiccup, followed by the fuel pump on LED illuminating - as soon as the electric pump provided sufficient pressure, the low pressure switch would open and the pump would shut off, and then back on, and then off. Ooops >>
My circuit published in the May 2008 issue of Kitplanes magazine will do what you describe including switch conditioning and relay driving. It is a simple programmable timer. Set it to run for say 4 minutes. This gives you plenty of time to notice the LED and turn on the manual pump switch. You would need some blocking diodes for the manual switch and a cockpit accessible fuse/circuit breaker to be able to override a stuck-on failure.
With the system you describe there should not be an engine hiccup. When the fuel pressure starts to drop there is still a bowl's worth of fuel in the carburetor. The pressure switch should turn on the pump and refill the carb long before the bowl is depleted.
Email me off list and I'll send you a revised schematic for this function.
Tom
[quote][b]
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user9253
Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan
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| Posted: Tue Nov 17, 2009 6:16 am Post subject: Fuel pump control |
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The RV-12 has a mechanical fuel pump on the engine and an electrical fuel pump near the fuel tank. The electric fuel pump runs continuously whenever the master switch is on. There is no discrete switch for the electric fuel pump. The pre-flight check is to turn on the master switch and observe the fuel pressure to be sure the electric pump is working. Then start the engine and watch for an increase in fuel pressure to be sure that the mechanical fuel pump is also working. Yes, it wastes electricity and wears out the electric fuel pump. On the other hand, most automotive fuel pumps last the life of the vehicle. Airplanes are used a lot less then cars. I would not expect the electric fuel pump in the RV-12 to wear out soon. The big advantage of wiring the electric fuel pump to run continuously is that it helps to prevent mismanagement of the fuel system, a major cause of accidents. The RV-12 fuel system does not have a fuel selector valve because there is only one fuel tank. There is no mixture control. The only thing for the pilot to mismanage is the emergency fuel shut-off valve handle that is located on the floor. The handle must be pulled up to shut off. The simpler the system is, the less chance for malfunction or error.
Joe
[quote][b]
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jpx(at)qenesis.com
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| Posted: Tue Nov 17, 2009 8:25 am Post subject: Fuel pump control |
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Thanks for everyone's replys. The following is exactly the trick I
was hoping for !
Jeff Page
Dream Aircraft Tundra #10
| Quote: | From: Steve Ruse <steve(at)wotelectronics.com>
Subject: Re: Fuel pump control
>
It is pretty simple to do this if you use a fuel pump and relay coil
that require the same voltage. Use a pressure sensor to control the
relay. Connect the relay output to the fuel pump AND to the relay
coil (input). That way when the fuel pump comes on (due to a low
pressure signal), the relay locks itself on, regardless of the state
of the pressure sensor. To turn the pump off, you would have a
momentary switch in the circuit that would break the connection to the
relay coil. This used to be called a "seal-in" circuit for industrial
controls.
Steve Ruse
|
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http://www.matronics.com/Navigator?AeroElectric-List |
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