In-the-tank fuel pumps cause death and destruction

wrote:

> On Fri, 29 Oct 2004 23:00:03 +0200 (CEST), Nomen Nescio
> > wrote:
>
>>Have you all observed that not one automobile has a drain valve installed
>>to the fuel tank? Obviously, a drain valve installed at the tank sump
>>would safely allow the complete drainage of a fuel tank before
>>in-tank-fuel
>>pump or fuel gauge sending unit servicing. To the drain valve, a length
>>of
>>hose would be attached and led to one or more 5 gallon Jerry cans. Once
>>drained, the fuel tanks are much safer to work on, although caution should
>>still be exercised.
>>
>>Attempting to drain a fuel tank by disconnecting the fuel outlet hose and
>>attaching a shop pump will drain all the usable fuel, but not all the
>>fuel. A gallon or more gasoline will be retained in the tank.
>>
>>Fuel tank drain valves have always been required on aircraft, but totally
>>ignored for cars. They are useful for draining water and or other
>>contaminants. I am sure that is a useful feature for mechanics trying to
>>efficiently diagnose or correct a refractory fuel system problem.
>>
>>There may be a few objections to a drain valve, but there are workarounds.
>>1. Makes it easy to steal fuel. 2. Vandalism and arson. 3. Accidental
>>collision damage to valve and resultant fuel leakage. 4. Leakage. 5.
>>Cost Workarounds are 1. build in key lock 2. build in key lock 3. Locate
>>tank higher than low point of nearby structures 4. install screw cap as
>>per fuel injection rail shraeder valve. 5. cost is a non-issue for safety,
>>particularly on $30,000 plus cars.
>>
>>A drainable fuel tank makes fuel pump servicing safer than presently;
>>however, an external pump design is still much safer yet. One reader
>>suggested that the mechanic wait until the fuel level is half or less --
>>good luck if you fill your tank and 10 minutes later the pump quits. When
>>the pump quits, the engine stops right now! Now, if you had a DUAL fuel
>>pump system, you actually could run the fuel level down. I have addressed
>>this issue befo dual pumps, automatic controls, and warning indicators
>>when one fails.
>>
>>Think your car is advanced? There are four self-locking nuts on a
>>Wal-Mart
>>shopping cart. They retain the casters. How many self-locking nuts are
>>on
>>your $30,000 car. My car has none that I'm aware of. Car manufacturers
>>will do anything to avoid self lockers because of cost. Instead, auto
>>engineers did their own work-around for plain fasteners. They specify
>>torques at least 150% the maximum recommended by fastener torque tables.
>>Check it out. Every important fastener on your car is overtightened and
>>overstressed.
>>
> 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.
I have found many locknuts on the vehicles I have, seems they use them where
necessary.
Some new cars you don't have to drop the tank. I found an Impala web site
and the site owner did several how-to's from changing wiper blades to the
fuel pump. In the Impala you remove the back seat and then there is a
access panel that you remove and then you can pull the pump out from there.
I assume other cars would be the same.