EFI Fuel Pump Dissected

[boscoe99]

https://www.youtube.com/watch?v=QbzEeWy1b3o

[robert graham]

Guess that's an automotive in-tank fuel pump?....I just had my mechanic replace the fuel pump in my 1996 Buick Roadmaster after 20 years and 200,000 miles, so it's a darn good design!.....but it still seems just a bit strange to me to have an electric motor running in a tank of gasoline!....but whatever works!

[zenoahphobic]

One wonders what happens at empty, when the fuel pump starves of fuel.

The systems I have looked at do not have cutout leaving the pump and importantly the armature submerged in fuel, so there is a situation where the armature and brushes can spark away in the gaseous void of the empty tank.

My understanding is that this void is filled with air, and therefore plenty of oxyg en from the atmosphere. Spark plus fuel vapour and oxygen, in my book means BOOM.

I haven't Google this, is this incentive to never run out fuel? Brushless would be far safer.

[panasonic]

I understand why there can be no ignition when the pump is submerged and full of fuel. I don't get what happens when it runs dry. Cant find the answer.

I guess it is very hard to create the right fuel/air mix inside the tank or VST. And the brushes in those pumps do not spark?

You don't hear of cars or outboards blowing up from faulty fuel pumps...At least I don't.

[boscoe99]

I understand why there can be no ignition when the pump is submerged and full of fuel. I don't get what happens when it runs dry. Cant find the answer.

I guess it is very hard to create the right fuel/air mix inside the tank or VST. And the brushes in those pumps do not spark?

You don't hear of cars or outboards blowing up from faulty fuel pumps...At least I don't.

For combustion to occur there has to be an air/fuel ratio within certain limits. Any vapor within a fuel pump would be much too rich to support combustion I would suppose.

[99yam40]

I agree with this, even the tank itself should have a lack of O2 even when empty. too rich to go boom

[zenoahphobic]

I agree with this, even the tank itself should have a lack of O2 even when empty. too rich to go boom

So it is true the vapour is too rich to ignite? So what happens when opening the fuel cap on a large and not so large empty tank, that was kept below atmospheric pressure and perhaps left off for a long time?

Is it a calculated risk that the size of the filler opening will not allow the vapour to escape readily ( as it expands through evaporisation) and then not readily let air in that mixes with the air that's in the tank (Brownian motion); and together with that initial air that enters through that suction when opening the fuel cap, not enough to ignite?

So back in the days of blissful ignorance it was perfectly alright with cigarette in mouth, to closely inspect the fuel level after lifting off caps off containers and tanks such as on motorcycles? Did shaking the container to see what was in there, actually a safe thing to do, because it vapourised the fuel enough to make it too rich to explode? Like two wrong actions really did make a right!

A calculated risk..... Is it assumed the engine, therefore the fuel pump, is off before the cap is opened, and that the tank will be filled to totally immerse the pump again and not the cap just replaced after letting air in? I.e. Is there a safety warning not to open/ leave open the fuel cap without refilling?
Perfect way to make a simple car bomb. Drain the fuel, leave the cap off or let air in by cutting the filler hose etc, the next person attempting to drive sets it off by turning the key.

Lots of ??? ***

[rodbolt17]

like I have said.
it is a blow through design.
never heard of one going boom in my 30+ years of dealing with blow through pumps.

[donsmarine]

elaborate what blow thru is please

[99yam40]

I am sure it has to do with the gas being pumped runs threw the motor for cooling and lubrication

[boscoe99]

Maybe he meant flow through.

[rodbolt17]

I call it blow through. the pump is on the bottom and the motor on the top.
the pump blows the gas through the motor armature and across the brush set then exits the motor body.

[donsmarine]

is this just auto gas tanks?

[boscoe99]

Should apply to any EFI auto gas tank or any Yamaha EFI VST HP pump.

[zenoahphobic]

I call it blow through. the pump is on the bottom and the motor on the top.
the pump blows the gas through the motor armature and across the brush set then exits the motor body.

I guess you call a liquid a gas, makes sense then Or bit of a Freudian slip, maybe the whole lot may blow someday.