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What the purpose of the fuel shutoff valve?


Why do many GA aircraft not have a “Both” fuel selector?How does this fuel pump work?Why does fuel vaporization in a carburetor cause a temperature decrease rather than a rise?Why is mixture lean recommended on the ground?What is the relationship between fuel mixture and RPM in a reciprocating engine?Why not leave an electric fuel pump on all the time?How is that there is no leak through the fuel vents during aerobatics maneuvers?Why doesn't the Convair 580 have check valves to prevent inadvertent fuel transfer?How do you lean mixture using only the instruments on a C172 Skyhawk?Are there design guidelines for sizing vent/surge tanks?






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Most GA planes have fuel shutoff vavle wich I don't quite understand the purpose of it if you can cutt the fuel flow with the mixture.
my theory is to prevent fuel flow at earlier stage for safety reasons?










share|improve this question









$endgroup$







  • 3




    $begingroup$
    If you're changing the mixture, doesn't that indicate the fuel is reaching the carb? Typically you don't want residual fuel sitting in the carburetor as it can break down and gum it up.
    $endgroup$
    – zymhan
    9 hours ago

















5












$begingroup$


Most GA planes have fuel shutoff vavle wich I don't quite understand the purpose of it if you can cutt the fuel flow with the mixture.
my theory is to prevent fuel flow at earlier stage for safety reasons?










share|improve this question









$endgroup$







  • 3




    $begingroup$
    If you're changing the mixture, doesn't that indicate the fuel is reaching the carb? Typically you don't want residual fuel sitting in the carburetor as it can break down and gum it up.
    $endgroup$
    – zymhan
    9 hours ago













5












5








5


1



$begingroup$


Most GA planes have fuel shutoff vavle wich I don't quite understand the purpose of it if you can cutt the fuel flow with the mixture.
my theory is to prevent fuel flow at earlier stage for safety reasons?










share|improve this question









$endgroup$




Most GA planes have fuel shutoff vavle wich I don't quite understand the purpose of it if you can cutt the fuel flow with the mixture.
my theory is to prevent fuel flow at earlier stage for safety reasons?







fuel-systems






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 9 hours ago









Mike no smith Mike no smith

855 bronze badges




855 bronze badges







  • 3




    $begingroup$
    If you're changing the mixture, doesn't that indicate the fuel is reaching the carb? Typically you don't want residual fuel sitting in the carburetor as it can break down and gum it up.
    $endgroup$
    – zymhan
    9 hours ago












  • 3




    $begingroup$
    If you're changing the mixture, doesn't that indicate the fuel is reaching the carb? Typically you don't want residual fuel sitting in the carburetor as it can break down and gum it up.
    $endgroup$
    – zymhan
    9 hours ago







3




3




$begingroup$
If you're changing the mixture, doesn't that indicate the fuel is reaching the carb? Typically you don't want residual fuel sitting in the carburetor as it can break down and gum it up.
$endgroup$
– zymhan
9 hours ago




$begingroup$
If you're changing the mixture, doesn't that indicate the fuel is reaching the carb? Typically you don't want residual fuel sitting in the carburetor as it can break down and gum it up.
$endgroup$
– zymhan
9 hours ago










3 Answers
3






active

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12












$begingroup$

It's both a maintenance and safety feature.



You need a way to cut off fuel flow to the engine compartment, either to work on the engine, or because of a fire at the engine, or because you are doing a forced landing and it helps reduce the risk of your entire fuel contents seeping onto your hot engine if you bend things a bit putting it down and a fuel line gets broken.



So you will always have a shutoff valve, and it's always somewhere upstream of the firewall.






share|improve this answer









$endgroup$




















    5












    $begingroup$

    Fuel shutoff valves are a hold over from the days of float style carburetors (and necessary on any float style carb system). With a float style carb when the fuel is on the bowl will fill up until the float floats up and shuts the flow off. Since gasoline becomes a vapor at ambient temperature the small pool in the carb will be constantly evaporating. As such the float will sink and refill the bowl. Given enough time this will drain the fuel tank. This vaporous fuel also fills the intake and can cause backfires or intake fires.



    The mixture is adjusted post bowl and merely leans you to the point of cutout which may not truly be a full stoppage of fuel.



    For fuel injected systems or systems that use some kind of blow through carb a shutoff valve is not strictly necessary for leak reasons but JohnK makes some good points on when its used for safety reasons. Some of these systems will also allow small paths for fuel to escape so a shutoff is often implemented to ensure total fuel stoppage.






    share|improve this answer











    $endgroup$




















      5












      $begingroup$

      The less technical, but accurate, answer is to meet the certification requirements of the FARs. Specifically, FAR 23.2430 is Airworthiness Standards for Fuel systems. It reads in part: (a)Each fuel system must-...(5) "Provide a means to safely remove or isolate the fuel stored in the system from the airplane"






      share|improve this answer









      $endgroup$















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        3 Answers
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        3 Answers
        3






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        $begingroup$

        It's both a maintenance and safety feature.



        You need a way to cut off fuel flow to the engine compartment, either to work on the engine, or because of a fire at the engine, or because you are doing a forced landing and it helps reduce the risk of your entire fuel contents seeping onto your hot engine if you bend things a bit putting it down and a fuel line gets broken.



        So you will always have a shutoff valve, and it's always somewhere upstream of the firewall.






        share|improve this answer









        $endgroup$

















          12












          $begingroup$

          It's both a maintenance and safety feature.



          You need a way to cut off fuel flow to the engine compartment, either to work on the engine, or because of a fire at the engine, or because you are doing a forced landing and it helps reduce the risk of your entire fuel contents seeping onto your hot engine if you bend things a bit putting it down and a fuel line gets broken.



          So you will always have a shutoff valve, and it's always somewhere upstream of the firewall.






          share|improve this answer









          $endgroup$















            12












            12








            12





            $begingroup$

            It's both a maintenance and safety feature.



            You need a way to cut off fuel flow to the engine compartment, either to work on the engine, or because of a fire at the engine, or because you are doing a forced landing and it helps reduce the risk of your entire fuel contents seeping onto your hot engine if you bend things a bit putting it down and a fuel line gets broken.



            So you will always have a shutoff valve, and it's always somewhere upstream of the firewall.






            share|improve this answer









            $endgroup$



            It's both a maintenance and safety feature.



            You need a way to cut off fuel flow to the engine compartment, either to work on the engine, or because of a fire at the engine, or because you are doing a forced landing and it helps reduce the risk of your entire fuel contents seeping onto your hot engine if you bend things a bit putting it down and a fuel line gets broken.



            So you will always have a shutoff valve, and it's always somewhere upstream of the firewall.







            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 8 hours ago









            John KJohn K

            35.8k1 gold badge62 silver badges118 bronze badges




            35.8k1 gold badge62 silver badges118 bronze badges























                5












                $begingroup$

                Fuel shutoff valves are a hold over from the days of float style carburetors (and necessary on any float style carb system). With a float style carb when the fuel is on the bowl will fill up until the float floats up and shuts the flow off. Since gasoline becomes a vapor at ambient temperature the small pool in the carb will be constantly evaporating. As such the float will sink and refill the bowl. Given enough time this will drain the fuel tank. This vaporous fuel also fills the intake and can cause backfires or intake fires.



                The mixture is adjusted post bowl and merely leans you to the point of cutout which may not truly be a full stoppage of fuel.



                For fuel injected systems or systems that use some kind of blow through carb a shutoff valve is not strictly necessary for leak reasons but JohnK makes some good points on when its used for safety reasons. Some of these systems will also allow small paths for fuel to escape so a shutoff is often implemented to ensure total fuel stoppage.






                share|improve this answer











                $endgroup$

















                  5












                  $begingroup$

                  Fuel shutoff valves are a hold over from the days of float style carburetors (and necessary on any float style carb system). With a float style carb when the fuel is on the bowl will fill up until the float floats up and shuts the flow off. Since gasoline becomes a vapor at ambient temperature the small pool in the carb will be constantly evaporating. As such the float will sink and refill the bowl. Given enough time this will drain the fuel tank. This vaporous fuel also fills the intake and can cause backfires or intake fires.



                  The mixture is adjusted post bowl and merely leans you to the point of cutout which may not truly be a full stoppage of fuel.



                  For fuel injected systems or systems that use some kind of blow through carb a shutoff valve is not strictly necessary for leak reasons but JohnK makes some good points on when its used for safety reasons. Some of these systems will also allow small paths for fuel to escape so a shutoff is often implemented to ensure total fuel stoppage.






                  share|improve this answer











                  $endgroup$















                    5












                    5








                    5





                    $begingroup$

                    Fuel shutoff valves are a hold over from the days of float style carburetors (and necessary on any float style carb system). With a float style carb when the fuel is on the bowl will fill up until the float floats up and shuts the flow off. Since gasoline becomes a vapor at ambient temperature the small pool in the carb will be constantly evaporating. As such the float will sink and refill the bowl. Given enough time this will drain the fuel tank. This vaporous fuel also fills the intake and can cause backfires or intake fires.



                    The mixture is adjusted post bowl and merely leans you to the point of cutout which may not truly be a full stoppage of fuel.



                    For fuel injected systems or systems that use some kind of blow through carb a shutoff valve is not strictly necessary for leak reasons but JohnK makes some good points on when its used for safety reasons. Some of these systems will also allow small paths for fuel to escape so a shutoff is often implemented to ensure total fuel stoppage.






                    share|improve this answer











                    $endgroup$



                    Fuel shutoff valves are a hold over from the days of float style carburetors (and necessary on any float style carb system). With a float style carb when the fuel is on the bowl will fill up until the float floats up and shuts the flow off. Since gasoline becomes a vapor at ambient temperature the small pool in the carb will be constantly evaporating. As such the float will sink and refill the bowl. Given enough time this will drain the fuel tank. This vaporous fuel also fills the intake and can cause backfires or intake fires.



                    The mixture is adjusted post bowl and merely leans you to the point of cutout which may not truly be a full stoppage of fuel.



                    For fuel injected systems or systems that use some kind of blow through carb a shutoff valve is not strictly necessary for leak reasons but JohnK makes some good points on when its used for safety reasons. Some of these systems will also allow small paths for fuel to escape so a shutoff is often implemented to ensure total fuel stoppage.







                    share|improve this answer














                    share|improve this answer



                    share|improve this answer








                    edited 7 hours ago

























                    answered 8 hours ago









                    DaveDave

                    74.1k4 gold badges148 silver badges266 bronze badges




                    74.1k4 gold badges148 silver badges266 bronze badges





















                        5












                        $begingroup$

                        The less technical, but accurate, answer is to meet the certification requirements of the FARs. Specifically, FAR 23.2430 is Airworthiness Standards for Fuel systems. It reads in part: (a)Each fuel system must-...(5) "Provide a means to safely remove or isolate the fuel stored in the system from the airplane"






                        share|improve this answer









                        $endgroup$

















                          5












                          $begingroup$

                          The less technical, but accurate, answer is to meet the certification requirements of the FARs. Specifically, FAR 23.2430 is Airworthiness Standards for Fuel systems. It reads in part: (a)Each fuel system must-...(5) "Provide a means to safely remove or isolate the fuel stored in the system from the airplane"






                          share|improve this answer









                          $endgroup$















                            5












                            5








                            5





                            $begingroup$

                            The less technical, but accurate, answer is to meet the certification requirements of the FARs. Specifically, FAR 23.2430 is Airworthiness Standards for Fuel systems. It reads in part: (a)Each fuel system must-...(5) "Provide a means to safely remove or isolate the fuel stored in the system from the airplane"






                            share|improve this answer









                            $endgroup$



                            The less technical, but accurate, answer is to meet the certification requirements of the FARs. Specifically, FAR 23.2430 is Airworthiness Standards for Fuel systems. It reads in part: (a)Each fuel system must-...(5) "Provide a means to safely remove or isolate the fuel stored in the system from the airplane"







                            share|improve this answer












                            share|improve this answer



                            share|improve this answer










                            answered 5 hours ago









                            AdamAdam

                            1,4386 silver badges10 bronze badges




                            1,4386 silver badges10 bronze badges



























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