Re: In-the-tank fuel pumps cause death and destruction

Excess fuel is returned back to the tank. What temperature does gasoline evaporate? Just that question should spark some thought. Now add heated fuel, heated by compression and being near a heat source ( engine ), that statement should provoke some thought as well. Take some gasoline, put it in a closed non-vented container and shake it, then open the lid, notice there is now pressure in the container? Try to draw liquid out of a sealed container, what happens? It collapses. So the tank is designed to hold a small amount of pressure made by the fuel vapors. This is a DOT requirement. There are two valves on a tank. One is in the fuel cap the other is the tank vent. This provides a sealed tank that holds a slight pressure of no more than 2.1 psi over atmospheric pressure.

No O2, no burn.

Still no O2.

dibtube? Do you mean the fill neck? Hole in the fuel tank system can be dangerous, but you need to look at basic laws of physics, you may not be so worried.

The same sheet-metal that makes the "fire-wall" also separates you from the fuel tank.

How many cars have you heard of that have exploded or caught fire from an in-tank fuel pump? In my case, the answer is zero so I don't lose much sleep over it.

I'm more worried about an inadvertant air bag deployment than I am about my gas tank exploding. The former is much more likely than that latter and I've heard of several occurrences of unintended airbag deployment.

Matt

Due to the lawyers I don't believe we have firewalls any more...... that would insinuate that a fire is possible. They are now called bulkheads. Bob

Pumping section (gerotor, turbine, or roller vane section as the case may be for a given design) of the pump is below the commutation section. Check valve in the fuel line keeping the pump full of fuel after pump is shut off. There will always be a column of liquid fuel above the pump commutation level.

See above.

See above. It may be that no single-point of failure will cause a problem. But, as with any system, you can hypothesize a **combination** of failures that would creat a problem (cutting the odds) - you'd have to argue whether or not such a combination of failures was credible. And statistically, those combinations *will* happen. Don't ask me why there haven't been real "unexplained" explosions.

Too much heat - fire and vapor lock potential in the modern engine compartment.

I hear you though. Do a google search on my name and rec.autos.makers.chrysler and "commutation" and you'll see that I was asking the same questions of Ford and Chrysler engineers when I was an engineering manager for fuel pump products as a supplier - you'd be surprised how many of them never even thought to ask the questions - it's just the way things were done since before they were hired, so they never thought about it.

I often said it to them, and I said it in this ng, that if in-tank fuel pumps had not been invented before now, and I thought of doing it, I, as an engineer, never would have suggested it in today's legal and corporate environment - I would have kept my mouth shut for career protection.

Actually, I seriously doubt that it would be being done now if it had not had several years of being done with no indication that it was a real problem. IOW - you could never prove, in theory, to a committe of lawyers, managers, insurers, and MBA's that there could never be a scenario that an explosion could not occur from some credible combination of (1) running the tank out of fuel and (2) a bad in-line check valve in the lines (allowing the liquid to drain back), and (3) someone turning the ignition key to "run" and the fuel pump running dry inside. Oh there will always be those who will have some explanation of why it could never really explode - but wipe out their knowledge that it has ever been done before and put them in the parallel universe where it has not been done before and ask them to be the first person to volunteer to sit in the first vehicle in which it was ever to be tried the first time it was cranked up, and see if they will do it. Everyone has great hindsight knowing that it is in reality apparently safe. But to know ahead of time for sure...?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Fuel vapour in a concentration much to rich to burn. (in other words - mabee a teensy weensy little bit of air mixed with a LOT of raw fuel.

Heh heh! Reminds me of the time in a presentation to NASA when I got reprimanded for referring to an activation switch on a joystick for a robotic arm to be used on the space shuttle as a "dead man switch" (this was a few months after the Challenger disaster). (After the meeting, I very quietly joked to a co-worker, "Hmmm - maybe I should have called it a "dead *astronaut* switch?", insinuating that the objection was to the use of the politically incorrect word "man" instead of the generic "person" or "astronaut".)

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Well *sure* you say that *now*. But would you have wanted to be the first engineer in history to propose doing that? 8^)

Can't argue with that.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

I've seen many early Japanese cars with such a device (Nissan Maxima, Toyota Crown / Cressida etc). Question is how often is it used (virtually never) Putting a drain on a fuel tank creates a potential leak source and requires greater cost and added weight for the vehicle to haul around (ditto for the dual fuel pump idea that was below).

My Personal Olds is almost 10 years old and well well over 160K still on the original fuel pump that should have been replaced last spring . Every part will wear out given enough time & miles. The safety issue is more of incompetence and negligence on the part of the repair shop.

My $0.02

I may have missed it earlier, but it is your opinion that money had a lot / a little / nothing to do with the design?

Cost of repair was not a consideration?

Most diesel tanks do. Most diesel engines also have water separators somewhere in the fuel system. There is a physical difference between gasoline and diesel fuel as to why.

Hi Bill...

I'd have to be several kinds of fool to debate you given your experience. :)

Perhaps though, we should together design a new system? I'm thinking of gravity... :)

Ken

You are so full of $hit your eyes are brown. NO fasteners on a car are overtorqued by design. The bolts that carry high torque are SPECIFICALLY designed to stand that torque.

As for fuel drains on fuel tanks, yes, aircraft have them. If a drop of water gets into the wrong place on an airplane you don't just pull over to the side of the road. You come down.

That said, there are good reasons for NOT putting drain valves in automotive fuel tanks. When I started in the trade, they were common. Drain PLUGS, just like in an oil pan. Taking them out to drain fuel was more dangerous than pulling a line and letting it drain. The extra working of the metal, and welding in of the "boss" for the drain caused the tanks to rust out around the drain.

On today's plastic tanks that would not be a problem, but in order for the drain to work as a drain it MUST be at the lowest point. Retention of the drain bolt in event of something being cought under the vehicle is a REAL issue, unlike the straw man you arer attempting to build around the in-tank pumps.

The tanks must NOT LEAK under any cercumstances for environmental, as well as safety reasons.

Also, it is ILLEGAL and UNSAFE to drain fuel into an open container. A proper, approved fuel drain unit is REQUIRED to safely drain a fuel tank. The fuel is drawn from the sealed tank, through an air-tight hose, into another sealed container that is GROUNDED to the vehicle being drained to avoid any chance of a static spark. Using this fuel drain unit, no fuel ever spills.

As for the in-tank pump - the fuel acts as the coolant for the fuel pump. In some it is even the lubricant. The pump is always fully submurged in fuel - either liquid of vapour. Fuel vapour is significantly heavier than air, so even if air gets into the tank, the pump never sees it. The vapour pressure of Gasoline ensures the tank is virtually always air-free. The flamability limits of gasoline ensure it will NOT be lit by the "sparks" at the pump motor brushes.

The electric fuel guage sender unit, basically an open rheostat, is MUCH more likely to cause a fire than the fuel pump - and has been in use since the late twenties. Never heard of a fire caused by the fuel guage.

Externally mounted pumps, unless engine driven and engine mounted, are open to corrosion which can perforate the pump case, allowing it to leak fuel. The connections are also open to corrosion - and they are exposed to air, which contains oxygen, which gasoline requires inorder to burn.. Also, fuel pumps are MUCH better at pushing fuel than sucking it, and fuel vapourizes at a lower temperature when under low pressure - so vapour lock is ALWAYS a possibility with front mounted pumps - while almost unheard of with intank "pusher" pumps.

With fuel injection, an engine driven pump poses a problem - how do you get fuel to the engine to start the engine, when the pump is driven by the engine? Yes, it was done with the diaphragm pumps running at roughly 5PSI for carbs - but with EFI it is not so simple. Go with mechanical FI instead??

Sure - with all the serious problems that go with that setup. You could not afford to own one - particularly if it had to meet emission standards.

I have worked on vehicles with vacuum operated fuel pumps - firewall mounted and gravity feeding to the carb, engine driven mechanical pumps, frame mounted electric pumps, both rotary centrigugal, rotary vane, rotary "roller cell" and plunger/diaphragm motor driven (AC) and solenoid driven (SU), and i n-tank electric pumps, both centrifugal and roller element and vane types.

By FAR the most trouble free have been the in-tank roller element and vane pumps. I have seen MANY of them go over 300,000 miles without a single problem. I have seen them last 20 years without a problem.

Up here in the salt belt a frame mounted pump of any description is doing well to last 10 years or 90,000 miles.

Engine driven diaphragm pumps - even with the old leaded gasoline, did good to go 10 years. 5 was a lot more common. With today's ethanol blended and oxygenated fuels they would not last much more than half as long..

I have yet to hear of a vehicle fire caused by an intank pump.

I have seen several fires caused by half-wits spilling gasoline while attempting to remove or drain a fuel tank - with or without intank pump, and either lighting a torch to snip off a stubborn tank strap bolt, or thoughlessly lighting up a smoke a few feet away. Or dropping an incandescent trouble light, or spilling gas on one.

Ive seen fires caused by gasoline vapour, spilling over the top of an open pail of gasoline and settling in the open drain of the shop, being ignited by a chance spark from either welding, cutting, grinding, dropping a tool, a dropped match or cig butt, etc.

I've seen fires caused by short circuits while working on a vehicle electrical system without disconnecting the battery ground - and even from some dim-wit trying to remove the battery power lead instead of the ground, and shorting the power to ground, blowing up the battery.

But NEVER from an intank fuel pump failure.

And I've been in the business a long time - and worked on vehicles from the early twenties to the 2000s.

If you have about a week to wait for the fuel to tranfer........

And speaking of vehicle fires -

There is one less Aerostar in Waterloo Ontario tonight - and almost one less house as well.

An appliance serviceman had his Aerostar parked on a customer's driveway, about 3 feet from the garage door for several hours while on a service call. Just when he was about to leave, the vehicle started on fire. Suspicion is it was a defective ignition switch, subject to recall, that was never replaced.

At any rate, I was on my way home when I saw a plume of black smoke billow up about a block away, so I turned in to see what was going on. The vinyl siding was dripping off the front of the house and the van was fully engaged. People were standing around watching, and I hollered for a garden hose and sprayed down the front of the van, keeping the flames from playing on the house like a blow-torch. It was almost 5 minutes before the fire trucks arrived, and although the truck was a total loss, and the siding and garage door were seriously singed, there was no actual "fire damage" to the house, and no-one was hurt. The plastic fuel tank, under the floor, and separated from a raging inferno by only a single layer of sheet metal, did not melt, burn, leak, or explode.

And the electrical part that started the fire was nowhere close to what we would consider to be a serious fire safety thrat like gasoline

- and there were no electrical "loads" connected at the time of the fire.

There have been NUMEROUS confirmed reports of fires being caused on these vehicles from this electrical defect, vs NO confirmed instances that I am aware of, of an intank fuel pump, even in operation, causing a fire.

Note relevance - it was a FORD.

No,, about half an hour maximum will empty a 72 liter tank - and totally unmonitored, so you can do another job while it is being drained. The schrader valve is removed to remove a significant amount of restriction from the line.

wouldn't the arcing be only where the actual motor assembly would be? could this not be a sealed unit? Would you even want gas in there? I would think gas does a poor job of lubrication - you'd have some kind of grease in the actual motor assembly, wouldn't you?

the gears that pump the gasoline won't be arcing...

fwiw, my fish tank pump uses a sealed pump assy with a magnetic drive assembly - no chance of water touching the electrical parts.

Ray

One other problem with external pumps. Noise. The tank acts as a nice muffler for the pump while. Plus the rubber on the tank straps deaden the sound even more.

My buddy's Nova with an external Holley electric pump whines. Fortunately, you can't hear it over the exhaust. ;)

Ray