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Boost Pump

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Joe Fisher

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Joined
Feb 10, 2007
Messages
1,379
Location
Galesburg, KS South east Kansas
I don't know what airplane you are working on.If your system is not all built it would be best to locate the boost pump as close to the fuel tank as possible best if the fuel pump can gravity feed so it doesn't have to suck fuel. And put it aft of the fire wall so it is not exposed to engine heat. Install the vapor vent line from the throttle servo to the fuel tank most home builders don't do this. The reason for these steps is the boost pump can over come a vapor lock at the engine driven fuel pump or the throttle servo. If you don't use the vapor vent you don't have a way to to expel the hot fuel vapor. This brings me to hot starts. If you have all of these features. Fuel on mixture cut off throttle closed turn on boost pump. Now do prestart check list allowing time for boost pump to circulate cool fuel in the engine driven fuel pump and throttle servo. Now open throttle 1/3dr crank engine 6 or 10 blades now slowly feed in mixture. Engine will start first time every time.
 

skeeter_ca

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Joined
Jun 29, 2005
Messages
1,027
Location
Yucaipa, Ca
Most(99.9%) Auto fuel pumps are in-tank units and they do have a check valve in the pump. It keeps fuel from back flowing into the tank and causing long crank times to start. Electric pumps push really good and mechanicals suck really good. (I know there a joke in there somewhere. Anywho....) If you can best to locate electrical pump in the tank, but that may not be practical with wing tanks, being they are so slim.

Alot of autos also use a return fuel system type where the fuel pump pressures the entire fuel rail and the fuel pressure regulator dumps any excessive fuel back to the fuel tank. This keeps vapor lock from happening. Some new vehicle use a returnless system those system have to have a fuel pressure sensor and the rail and the fuel pump is modulated by the PCM to maintain correct pressure and volume. Very complicated programming process.

skeeter
 

Joe Fisher

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Joined
Feb 10, 2007
Messages
1,379
Location
Galesburg, KS South east Kansas
Well Skeeter you don't get it. The boost pump is used as a backup for the engine driven pump and dose not run except to start the engine and if the engine driven pump fails to provide the fuel to the throttle servo. So the check valve I describe is used to allow the fuel to flow around the boost pump when it is not operating. Aircraft fuel injection typically operates on 12 to 18 psi. There is almost nothing in common with aircraft fuel injection and automotive fuel injection. The fuel pumps Jgnunn is considering would normally be used with auto carburetors.
 

skeeter_ca

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Joined
Jun 29, 2005
Messages
1,027
Location
Yucaipa, Ca
Ahh... i get it now. I was assuming (wrongfully) that he was using an aftermarket type automotive fuel injection system. I could not tell that he was talking about a cert. lyc/cont engine instead of a auto conversion. I understand your statement now for the check valve if you are bypassing the pump. However the auto pumps do have a check valve in them. At least the last 200 pumps i've replaced did. They also produce about 60psi max. Way more than the 12 to 18 you state is needed. I am not sure if they would cause to much restriction trying to suck thru them when they are off. If it did the situation would warrant plumbing a bypass around the pump and installing a check valve as you described. That would be an interesting test.

skeeter
 

jgnunn

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Joined
Aug 7, 2005
Messages
175
Location
Jarrell, TX. Fly out of Taylor-T74
Good assumption. Crazy pricing. The boost pump needs to run around 24-25 PSI for the IO-360, I believe. There are many auto options out there, they just need a regulator with a return line and even tho some state they have open flow when the pump is off, I would still install a bypass and check valve, just in case.
 
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