Fuel selector or two check valves?

[Rob Turk]

Instead of using a left/right fuel selector, could I use two check valves
and connect the two tanks into a single feed?

[LTANK]--->|-----T-----|<-----[RTANK]

Where >| and |< are the check valves and 'T' is a T-connector towards the
header tank.
The check valves prevent fuel moving from one tank to the other. Any pro's,
con's or thoughts?

Rob

[Edgar]

"Rob Turk" > wrote in message
news:SN6we.366$in3.124@amstwist00...
> Instead of using a left/right fuel selector, could I use two check valves
> and connect the two tanks into a single feed?
>
> [LTANK]--->|-----T-----|<-----[RTANK]
>
> Where >| and |< are the check valves and 'T' is a T-connector towards the
> header tank.
> The check valves prevent fuel moving from one tank to the other. Any
pro's,
> con's or thoughts?

I'd want more control over the actual fuel usage than a check valve will
give me. The selector valve will allow you to use fuel from the 'heavy side'
to properly level out- check valves will not allow this. Then you can leave
the selector valve on 'both' for normal conditions.

[Rob Turk]

"Edgar" > wrote in message
...
>
> "Rob Turk" > wrote in message
> news:SN6we.366$in3.124@amstwist00...
>> Instead of using a left/right fuel selector, could I use two check valves
>> and connect the two tanks into a single feed?
>>
>> [LTANK]--->|-----T-----|<-----[RTANK]
>>
>> Where >| and |< are the check valves and 'T' is a T-connector towards
>> the
>> header tank.
>> The check valves prevent fuel moving from one tank to the other. Any
> pro's,
>> con's or thoughts?
>
> I'd want more control over the actual fuel usage than a check valve will
> give me. The selector valve will allow you to use fuel from the 'heavy
> side'
> to properly level out- check valves will not allow this. Then you can
> leave
> the selector valve on 'both' for normal conditions.
>

Wouldn't gravity take care of leveling the two tanks? That way there
wouldn't be a heavy side. My assumption is that the fullest one will create
more pressure, causing it to level automatically. Wrong assumption?!? This
is on a high-wing plane by the way..

Rob

[Drew Dalgleish]

>Wouldn't gravity take care of leveling the two tanks? That way there
>wouldn't be a heavy side. My assumption is that the fullest one will create
>more pressure, causing it to level automatically. Wrong assumption?!? This
>is on a high-wing plane by the way..
>
>Rob
>
>
I think that your tanks will not feed evenly because of little
differences in the way the lines run and venting. You will also lose
the ability to run one tank dry to extend your range. On my murphy
rebel one tank feeds a lot faster than the other one when I'm running
on both.

[Mark Smith]

Drew Dalgleish wrote:
>
> >Wouldn't gravity take care of leveling the two tanks? That way there
> >wouldn't be a heavy side. My assumption is that the fullest one will create
> >more pressure, causing it to level automatically. Wrong assumption?!? This
> >is on a high-wing plane by the way..
> >
> >Rob
> >
> >
> I think that your tanks will not feed evenly because of little
> differences in the way the lines run and venting. You will also lose
> the ability to run one tank dry to extend your range. On my murphy
> rebel one tank feeds a lot faster than the other one when I'm running
> on both.


Very dependent on how far below the tank outlet the two lines/valve
connects the two feed lines,,,,,,,,,,

a connection that is level with the tank outlets will very likely have
trouble feeding both tanks evenly,

a much lower connection won't care,,,,,,,,,
--
Mark Smith
Tri-State Kite Sales
1121 N Locust St
Mt Vernon, IN 47620
1-812-838-6351
http://www.trikite.com

[Drew Dalgleish]

On Tue, 28 Jun 2005 12:54:20 GMT, Mark Smith > wrote:

>Drew Dalgleish wrote:
>>
>> >Wouldn't gravity take care of leveling the two tanks? That way there
>> >wouldn't be a heavy side. My assumption is that the fullest one will create
>> >more pressure, causing it to level automatically. Wrong assumption?!? This
>> >is on a high-wing plane by the way..
>> >
>> >Rob
>> >
>> >
>> I think that your tanks will not feed evenly because of little
>> differences in the way the lines run and venting. You will also lose
>> the ability to run one tank dry to extend your range. On my murphy
>> rebel one tank feeds a lot faster than the other one when I'm running
>> on both.
>
>
>Very dependent on how far below the tank outlet the two lines/valve
>connects the two feed lines,,,,,,,,,,
>
>a connection that is level with the tank outlets will very likely have
>trouble feeding both tanks evenly,
>
>a much lower connection won't care,,,,,,,,,

that may usually be the case but on my plane the connection is at the
firewall just ahead of the gascolator. thats almost 3' difference in
height. When I did my fuel flow test the tanks flowed the same amount.



>Mark Smith
>Tri-State Kite Sales
>1121 N Locust St
>Mt Vernon, IN 47620
>1-812-838-6351
> http://www.trikite.com

[Dave S]

Is the fuel above or below the engine (high wing or low wing?)

it IS possible in a low wing configuration for one tank to completely
drain and then suck air.

The answer to that is to use a sump or gravity fed header tank.

The Velocity plans call for two strake mounted tanks, draining into a
single sump, from there the fuel is fed to the engine. In practice the
two strake tanks and sump function as a single fuel tank. The check
valve isnt necessary.

Dave

Rob Turk wrote:
> Instead of using a left/right fuel selector, could I use two check valves
> and connect the two tanks into a single feed?
>
> [LTANK]--->|-----T-----|<-----[RTANK]
>
> Where >| and |< are the check valves and 'T' is a T-connector towards the
> header tank.
> The check valves prevent fuel moving from one tank to the other. Any pro's,
> con's or thoughts?
>
> Rob
>
>

[Al]

How would you shut off the fuel? Let's say in the case of fire. Al


"Rob Turk" > wrote in message
news:SN6we.366$in3.124@amstwist00...
> Instead of using a left/right fuel selector, could I use two check valves
> and connect the two tanks into a single feed?
>
> [LTANK]--->|-----T-----|<-----[RTANK]
>
> Where >| and |< are the check valves and 'T' is a T-connector towards the
> header tank.
> The check valves prevent fuel moving from one tank to the other. Any
> pro's, con's or thoughts?
>
> Rob
>
>

[Mark Smith]

Drew Dalgleish wrote:
>
> On Tue, 28 Jun 2005 12:54:20 GMT, Mark Smith > wrote:
>
> >Drew Dalgleish wrote:
> >>
> >> >Wouldn't gravity take care of leveling the two tanks? That way there
> >> >wouldn't be a heavy side. My assumption is that the fullest one will create
> >> >more pressure, causing it to level automatically. Wrong assumption?!? This
> >> >is on a high-wing plane by the way..
> >> >
> >> >Rob
> >> >
> >> >
> >> I think that your tanks will not feed evenly because of little
> >> differences in the way the lines run and venting. You will also lose
> >> the ability to run one tank dry to extend your range. On my murphy
> >> rebel one tank feeds a lot faster than the other one when I'm running
> >> on both.
> >
> >
> >Very dependent on how far below the tank outlet the two lines/valve
> >connects the two feed lines,,,,,,,,,,
> >
> >a connection that is level with the tank outlets will very likely have
> >trouble feeding both tanks evenly,
> >
> >a much lower connection won't care,,,,,,,,,
>
> that may usually be the case but on my plane the connection is at the
> firewall just ahead of the gascolator. thats almost 3' difference in
> height. When I did my fuel flow test the tanks flowed the same amount.
>


I'd bet mine would too, on the ground,

but in the air, they were several inches different, and with a tank that
is pretty thin, it is a bunch of fuel, or air, since the pump will suck
air from the empty tank rather than fuel from the partially full one,

I solved it by installing two small forward pointing tubes that mount on
the caps,,,,
--
Mark Smith
Tri-State Kite Sales
1121 N Locust St
Mt Vernon, IN 47620
1-812-838-6351
http://www.trikite.com

[Rob Turk]

"Al" > wrote in message
news:1119973229.7b47c562c0536a3cc6ea1419507bddbe@t eranews...
> How would you shut off the fuel? Let's say in the case of fire. Al
>
>

The full picture is a bit more complex (isn't it always...)

This is a high-wing plane (Rans S6S). Both main tanks have breather pipes to
pressurise the tanks during flight. The fuel lines from the tanks flow into
separate entries of a fuel buffer tank (approx 1.5 Gallon) placed low, below
the luggage compartment. From the buffer tank a single feed goes through a
Facet pump (just in case), then through the fuel filter to a shut-off valve
near the firewall, within easy reach of the pilot. Then through the firewall
into a gascolator. Output of the gascolator goes to the mechanical pump on
the Jabiru engine, then to the carburettor.

The overflow of the gascolator goes through a check valve, then through a
return line into the buffer tank.

What I'm trying to determine is if I should use separate cut-off valves in
the lines from the main tanks to the buffer, or that I can use check valves
instead.

Rob

[[email protected]]

Use separate valves if the tanks aren't vented to the same
source. For certified aircraft, any gravity-feed system that uses one
valve or a valve with a "Both" position must have the tanks vented to
the same source to keep tank pressures equal. Many homebuilts have
problems along this line and a few have quit and crashed because the
builder made mods and/or didn't understand the reasons the designer
made things the way he did. Even some designs had shortcomings to start
with. The original Glastar design, for instance, had a vent tube under
each wingtip to feed each tank separately, and small differences in ram
air pressure would cause one tank to drain before the other. If the
pressure differential is large enough, the tank with lower pressure
will not flow at all and the engine will quit when the other runs dry.
The Cessna 150 used a single valve to control the flow from both
tanks, teed together at the valve inlet, and the tanks were both
connected to the single vent under the left wing. You could still get
uneven flow if you flew with one wing a bit low; remember that the
tanks are well apart and a slight bank will raise one above the other
to cause crossflow. Check valves could stop that, but they'd have to be
installed as low as possible so that the small amount of head pressure
will open them, and their springs would have to be very weak. My old
Auster had such check valves but still used two shutoffs because the
tanks were separately vented at the caps.
If I was to build another airplane I'd have shutoffs right at the
tank outlets; maintenance on the system is a pain if you have to drain
the tanks every time you want to fix something, and it would be nice to
have them there in case of a leak lower down in the system while in
flight.

Dan

[[email protected]]

wrote:
>
> ...
>
> You could still get
> uneven flow if you flew with one wing a bit low; remember that the
> tanks are well apart and a slight bank will raise one above the other
> to cause crossflow. Check valves could stop that, but they'd have to be
> installed as low as possible so that the small amount of head pressure
> will open them, and their springs would have to be very weak. My old
> Auster had such check valves but still used two shutoffs because the
> tanks were separately vented at the caps.

I'll add that check valves present an unwanted resistance to flow in
the intended direction, minimization of that effect tends to go
hand-in-hand with reduce reliably and completeness of closure when
the pressure is reversed.

> If I was to build another airplane I'd have shutoffs right at the
> tank outlets; maintenance on the system is a pain if you have to drain
> the tanks every time you want to fix something, and it would be nice to
> have them there in case of a leak lower down in the system while in
> flight.
>

For that application, would not full-aperture ball valves be
appropriate?

--

FF

[[email protected]]

>For that application, would not full-aperture ball >valves be
>appropriate?

Yup. I use one in my Jodel now; they work fine, but a weak point
appears to be the o-ring around the shaft. The ball and teflon seats
work OK. Watch that you don't get a really poor quality Asian unit;
there's a wide range of stuff from good to pretty lousy out there.
Badly cut pipe threads and all.

Dan

[Blueskies]

"Rob Turk" > wrote in message news:SN6we.366$in3.124@amstwist00...
> Instead of using a left/right fuel selector, could I use two check valves and connect the two tanks into a single
> feed?
>
> [LTANK]--->|-----T-----|<-----[RTANK]
>
> Where >| and |< are the check valves and 'T' is a T-connector towards the header tank.
> The check valves prevent fuel moving from one tank to the other. Any pro's, con's or thoughts?
>
> Rob
>


What is the pressure drop through the valve and the cracking pressure of the valve? Pretty hard to have 'matched'
valves, so one will most likely flow freer...