In-Tank Fuel Pump Electrical Question

[Tom in Virginia]

Can someone explain how an in-tank fuel pump with 6 different electrical wires/connections (see picture of pump) can be immersed in a tank filled with gasoline not cause the tank to explode or cause any kind of fire?  

I took my tank off and pulled the fuel pump unit.  Plan was to replace the fuel filter but it back flowed onto a clean cloth with very little to no sediment and the filter is a metal one so assume it has been replaced at least once prior.  Also did not have the proper hose clamps and crimper to reattach the filter to the hose.  While I was in there planned to replace fuel pump as routine maintenance.  Admittedly I am reluctant since I would have to cut wires and remake connections.  With concerns for how to properly electrically connect wiring inside of a tank that holds highly flammable liquid, I decided it best just to reassemble the pump unit into the tank and put off until I have more knowledge on the subject/maintenance.  Thus the lead in question.

The metal foil tape covering the heat resistant cloth on the underside of the tank was showing its age and a bit knackered so I recovered it to give it some more life. 

Thanks in advance for the knowledge and suggestions.

[gstallons]

First answer ; there is not enough air in the tank to allow a "burn" to take place . 

[Lucky Phil]

1 hour ago, Tom in Virginia said:

Can someone explain how an in-tank fuel pump with 6 different electrical wires/connections (see picture of pump) can be immersed in a tank filled with gasoline not cause the tank to explode or cause any kind of fire?  

I took my tank off and pulled the fuel pump unit.  Plan was to replace the fuel filter but it back flowed onto a clean cloth with very little to no sediment and the filter is a metal one so assume it has been replaced at least once prior.  Also did not have the proper hose clamps and crimper to reattach the filter to the hose.  While I was in there planned to replace fuel pump as routine maintenance.  Admittedly I am reluctant since I would have to cut wires and remake connections.  With concerns for how to properly electrically connect wiring inside of a tank that holds highly flammable liquid, I decided it best just to reassemble the pump unit into the tank and put off until I have more knowledge on the subject/maintenance.  Thus the lead in question.

The metal foil tape covering the heat resistant cloth on the underside of the tank was showing its age and a bit knackered so I recovered it to give it some more life. 

Thanks in advance for the knowledge and suggestions.

There is an old demonstration I saw 40 or so years ago of an arcing wire submerged in fuel, just arcing . To get an explosion you need 3 components, fuel, an ignition source and oxygen. Under normal conditions the tank has only 1 of these, fuel. I'm not entirely sure that a closed tank with low fuel would actually have enough oxygen to support ignition if arcing did happen.An open tank would be another thing though. 

Why would you need to do any wiring repairs to replace the pump? aren't they all plug connectors in there?

Ciao     

[Weegie]

I'm no expert but what Phil stated is how I understand it too, the fire triangle, with the 3 elements coming together.

I'm sceptical about "the not enough Oxygen/air in the tank to take place" hypothesis, AFAIK tanks are vented therefore anything above the fuel level could be an explosive mixture. Depends on the surface area, temperature and probably other variables, that would determine fuel evaporation rate. If that stays below a threshold then it's fine. There either there isn't enough air (when the tank is full) or there isn't enough vapour when the tank is nearer empty

The risk cold also be mitigated in the tank design by always having the pump suction above the electrical connections but I don't know and from that picture it doesn't look like it. If the connections get exposed then there would be a risk. That can be ellimated through wiring and connectors designed specifically for hazardous environments.

If I ever found myself having to repair wiring where it entered the tank I'd be making sure I used suitable connectors and wiring.

I've heard of plenty tanks expoding when being worked on without being sufficiently purged usually welding in the past, but never a tank exploding or bursting into flames due to bad electrics in the tank.

[Tom in Virginia]

https://www.mgcycle.com/index.php?main_page=product_info&cPath=30&products_id=5389

The MG Cycle fuel pump is supplied with a pigtail, but if the old wiring/connector is in good shape and the fuel pump connector is compatible then I may not have to make any "connections" other than plug and play.  That avoids incurring any wiring challenges.  Another concern was having to mess with the wiring penetration at the base of the fuel pump foundation where all 4 wires penetrate the rubber tank grommet and exit the tank to the external plug in connectors.

The fuel pump is not all that expensive so that'll be in hand, as well as the hose clamps and crimping tool, and added to my winter tear down work list when I take the tank off again.

3 hours ago, gstallons said:

First answer ; there is not enough air in the tank to allow a "burn" to take place . 

Yes, I guess once the tank is closed, then there may be gas fumes in the void above the liquid fuel but not per se "oxygen".

 

3 hours ago, Lucky Phil said:

Why would you need to do any wiring repairs to replace the pump? aren't they all plug connectors in there?

Ciao     

I certainly hope so Phil, the "pig tail" in the MG Cycle link kinda made me think I need to do something more than just plug in.

[gstallons]

FWIW : old garages used to weld up rusty fuel tanks . They would remove the tanks and run an exhaust pipe into the empty fuel tank , poke a hole ( about 3/8'' ) into the uppermost part of the tank , start up the donor car . After a few minutes , braze , led or weld away . After finishing , they would fill in the man made hole and call it good . 

 I'm not sure if these were men or fools ?

[Tom in Virginia]

55 minutes ago, gstallons said:

FWIW : old garages used to weld up rusty fuel tanks . They would remove the tanks and run an exhaust pipe into the empty fuel tank , poke a hole ( about 3/8'' ) into the uppermost part of the tank , start up the donor car . After a few minutes , braze , led or weld away . After finishing , they would fill in the man made hole and call it good . 

 I'm not sure if these were men or fools ?

 Wait now, you are speaking of a Kentucky garage, right?   Makes sense though, they were essentially purging the tank with carbon monoxide and various other gases.

 

Edited August 29, 2020 by Tom in Virginia

[gstallons]

Yep . But dumbass antics aren't exclusive to The Bluegrass State .  

My ex wife's grandfather had a fuel tank off a Model T (I think) because he thought it had water in the tank . He was straddling the tank as it was on the ground , he lit a match and got it near the neck of the tank to look inside . KABOOOM , he looked like a 300 lb. cartoon character going 15' in the air ! When he regained consciousness , he decided the tank was clean and no longer useful.

[Nihontochicken]

I've always been leery of electrics inside the gas tank.  The "air" space above the liquid is generally near 100% gas fumes, but there is a chance that some real air (oxygen) can get in and make the mixture explosive, particularly in a nearly empty tank.  The most infamous fuel tank explosion occurred in TWA Flight 800 over NY City in 1976.  Note that jet fuel (kerosene) is not as inherently explosive as is gasoline.  Here's a link to the Wiki coverage:

https://en.wikipedia.org/wiki/TWA_Flight_800

[po18guy]

12 minutes ago, Nihontochicken said:

I've always been leery of electrics inside the gas tank.  The "air" space above the liquid is generally near 100% gas fumes, but there is a chance that some real air (oxygen) can get in and make the mixture explosive, particularly in a nearly empty tank.  The most infamous fuel tank explosion occurred in TWA Flight 800 over NY City in 1976.  Note that jet fuel (kerosene) is not as inherently explosive as is gasoline.  Here's a link to the Wiki coverage:

https://en.wikipedia.org/wiki/TWA_Flight_800

That is the best guess. But, it stretches my credulity to believe that fuel which is fairly difficult to ignite unless atomized would ignite explosively in response to a low voltage spark. In any event, if a motorcycle was to spontaneously explode from an internal pump, it would have to be some form of Guzzi. I know of no such case.

[Nihontochicken]

4 minutes ago, po18guy said:

That is the best guess. But, it stretches my credulity to believe that fuel which is fairly difficult to ignite unless atomized would ignite explosively in response to a low voltage spark. In any event, if a motorcycle was to spontaneously explode from an internal pump, it would have to be some form of Guzzi. I know of no such case.

Hahahaha!  Ain't that the truth!  Of course, Guzzi has a grand tradition of tank fires.  For the few here who might be unaware, the first MG LeMans editions had a metal tank with a spring  loaded cap locked with a spring detente.  They lacked the rocker cover add-on spark plug protectors that later models have.  So when an unfortunate rider dropped his running LeMans, the impact would pop open the gas cap at the same time the asphalt broke free the spark plug wire.  Fuel, check.  Ignition source, check.  Oxygen, check.  Voila, the patented Moto Guzzi LeMans tank fire, grab the marshmallows!  An unfortunate end to a number of noble steeds. 

[Tom in Virginia]

2 hours ago, Nihontochicken said:

I've always been leery of electrics inside the gas tank.  The "air" space above the liquid is generally near 100% gas fumes, but there is a chance that some real air (oxygen) can get in and make the mixture explosive, particularly in a nearly empty tank.  The most infamous fuel tank explosion occurred in TWA Flight 800 over NY City in 1976.  Note that jet fuel (kerosene) is not as inherently explosive as is gasoline.  Here's a link to the Wiki coverage:

https://en.wikipedia.org/wiki/TWA_Flight_800

Wikipedia:  "The report's conclusion was that the probable cause of the accident was explosion of flammable fuel vapors in the center fuel tank. Although it could not be determined with certainty, the likely ignition source was a short circuit.^[1]:xvi Problems with the aircraft's wiring were found, including evidence of arcing in the Fuel Quantity Indication System (FQIS) wiring that enters the tank. The FQIS on Flight 800 is known to have been malfunctioning; the captain remarked on what he called "crazy" readings from the system approximately two minutes and thirty seconds before the aircraft exploded. As a result of the investigation, new requirements were developed for aircraft to prevent future fuel tank explosions.^[9]"

^{Lesson learned: If your fuel gauge starts giving you crazy readings, BAIL OUT!!!}

[Lucky Phil]

2 hours ago, Tom in Virginia said:

Wikipedia:  "The report's conclusion was that the probable cause of the accident was explosion of flammable fuel vapors in the center fuel tank. Although it could not be determined with certainty, the likely ignition source was a short circuit.^[1]:xvi Problems with the aircraft's wiring were found, including evidence of arcing in the Fuel Quantity Indication System (FQIS) wiring that enters the tank. The FQIS on Flight 800 is known to have been malfunctioning; the captain remarked on what he called "crazy" readings from the system approximately two minutes and thirty seconds before the aircraft exploded. As a result of the investigation, new requirements were developed for aircraft to prevent future fuel tank explosions.^[9]"

^{Lesson learned: If your fuel gauge starts giving you crazy readings, BAIL OUT!!!}

Yes, but aircraft fuel tanks are vented much more effectively than a motorcycle tank in that they are virtually open to atmosphere by large vents. There was a 737-800 that caught fire at the gate in the Philippines a while back as well from memory attributed to an ctr tank fire.I think from memory it had to do with very hot weather, low tank qty and a/c packs running for hours as contributors. I'll need to look it up.  

Commercial jets also have their pumps in a dry bay usually to isolate them from the actual surrounding fuel which makes the tank fires even more unusual, that combined with JetA1 being way less volatile than gasoline.

Ciao

 

   

[docc]

Have not passenger vehicles had their fuel pumps inside the tank for decades without issue?

[Lucky Phil]

57 minutes ago, docc said:

Have not passenger vehicles had their fuel pumps inside the tank for decades without issue?

Yep and plastic tanks as well.

Ciao